From 21ff9ded5931bb381d7d4719fe618fe131c76a67 Mon Sep 17 00:00:00 2001
From: Selene Chew <selene.chew@kensho.com>
Date: Wed, 7 Apr 2021 11:52:29 -0400
Subject: [PATCH 1/5] WIP SimpleExecute

---
 Pipfile                                       |   3 +-
 Pipfile.lock                                  | 551 +++++++++++-------
 .../compiler/compiler_frontend.py             |  18 +-
 .../query_planning_and_execution/__init__.py  |   1 +
 .../make_query_plan.py                        |   2 +-
 .../sync_query_execution.py                   |  35 ++
 .../query_planning_and_execution/typedefs.py  | 251 ++++++++
 .../test_make_query_plan.py                   |   2 +-
 setup.py                                      |   4 +-
 9 files changed, 636 insertions(+), 231 deletions(-)
 create mode 100644 graphql_compiler/query_planning_and_execution/__init__.py
 rename graphql_compiler/{schema_transformation => query_planning_and_execution}/make_query_plan.py (99%)
 create mode 100644 graphql_compiler/query_planning_and_execution/sync_query_execution.py
 create mode 100644 graphql_compiler/query_planning_and_execution/typedefs.py

diff --git a/Pipfile b/Pipfile
index 6d4960e61..ec6afa9ab 100755
--- a/Pipfile
+++ b/Pipfile
@@ -40,10 +40,11 @@ sphinx = ">=1.8,<2"
 
 [packages]  # Make sure to keep in sync with setup.py requirements.
 ciso8601 = ">=2.1.3,<3"
+dataclasses-json = ">=0.5.2,<0.6"
 funcy = ">=1.7.3,<2"
 graphql-core = ">=3.1.2,<3.2"  # minor versions sometimes contain breaking changes
 six = ">=1.10.0"
-sqlalchemy = ">=1.3.0,<2"
+sqlalchemy = ">=1.3.0,<1.4"
 
 # The below is necessary to make a few pylint passes work properly, since pylint expects to be able
 # to run "import graphql_compiler" in the environment in which it runs.
diff --git a/Pipfile.lock b/Pipfile.lock
index c857fb500..e1da09387 100644
--- a/Pipfile.lock
+++ b/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "3cb98c3dd25e1ed97827a7776f87def23c3112f56b8e5a6cb06119e7559ed6b6"
+            "sha256": "cccd3a7f57d64a4d4e40bcc9881b91001c99832d42b31d9f5c0ea5a6aa9ec5a8"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -23,6 +23,14 @@
             "index": "pypi",
             "version": "==2.1.3"
         },
+        "dataclasses-json": {
+            "hashes": [
+                "sha256:56ec931959ede74b5dedf65cf20772e6a79764d20c404794cce0111c88c085ff",
+                "sha256:b746c48d9d8e884e2a0ffa59c6220a1b21f94d4f9f12c839da0a8a0efd36dc19"
+            ],
+            "index": "pypi",
+            "version": "==0.5.2"
+        },
         "funcy": {
             "hashes": [
                 "sha256:65b746fed572b392d886810a98d56939c6e0d545abb750527a717c21ced21008",
@@ -37,11 +45,33 @@
         },
         "graphql-core": {
             "hashes": [
-                "sha256:b1826fbd1c6c290f7180d758ecf9c3859a46574cff324bf35a10167533c0e463",
-                "sha256:c056424cbdaa0ff67446e4379772f43746bad50a44ec23d643b9bdcd052f5b3a"
+                "sha256:95b0d6510bb5532dcac5927f5dfd674a580b33d6ba6417c3dc75086d9a210c83",
+                "sha256:db599b57b0f7dc13541922a83b30192be573b7143330ef3613813942ce4073a0"
             ],
             "index": "pypi",
-            "version": "==3.1.2"
+            "version": "==3.1.3"
+        },
+        "marshmallow": {
+            "hashes": [
+                "sha256:0dd42891a5ef288217ed6410917f3c6048f585f8692075a0052c24f9bfff9dfd",
+                "sha256:16e99cb7f630c0ef4d7d364ed0109ac194268dde123966076ab3dafb9ae3906b"
+            ],
+            "markers": "python_version >= '3.5'",
+            "version": "==3.11.1"
+        },
+        "marshmallow-enum": {
+            "hashes": [
+                "sha256:38e697e11f45a8e64b4a1e664000897c659b60aa57bfa18d44e226a9920b6e58",
+                "sha256:57161ab3dbfde4f57adeb12090f39592e992b9c86d206d02f6bd03ebec60f072"
+            ],
+            "version": "==1.5.1"
+        },
+        "mypy-extensions": {
+            "hashes": [
+                "sha256:090fedd75945a69ae91ce1303b5824f428daf5a028d2f6ab8a299250a846f15d",
+                "sha256:2d82818f5bb3e369420cb3c4060a7970edba416647068eb4c5343488a6c604a8"
+            ],
+            "version": "==0.4.3"
         },
         "six": {
             "hashes": [
@@ -53,47 +83,65 @@
         },
         "sqlalchemy": {
             "hashes": [
-                "sha256:04f995fcbf54e46cddeb4f75ce9dfc17075d6ae04ac23b2bacb44b3bc6f6bf11",
-                "sha256:0c6406a78a714a540d980a680b86654feadb81c8d0eecb59f3d6c554a4c69f19",
-                "sha256:0c72b90988be749e04eff0342dcc98c18a14461eb4b2ad59d611b57b31120f90",
-                "sha256:108580808803c7732f34798eb4a329d45b04c562ed83ee90f09f6a184a42b766",
-                "sha256:1418f5e71d6081aa1095a1d6b567a562d2761996710bdce9b6e6ba20a03d0864",
-                "sha256:17610d573e698bf395afbbff946544fbce7c5f4ee77b5bcb1f821b36345fae7a",
-                "sha256:216ba5b4299c95ed179b58f298bda885a476b16288ab7243e89f29f6aeced7e0",
-                "sha256:2ff132a379838b1abf83c065be54cef32b47c987aedd06b82fc76476c85225eb",
-                "sha256:314f5042c0b047438e19401d5f29757a511cfc2f0c40d28047ca0e4c95eabb5b",
-                "sha256:318b5b727e00662e5fc4b4cd2bf58a5116d7c1b4dd56ffaa7d68f43458a8d1ed",
-                "sha256:3ab5b44a07b8c562c6dcb7433c6a6c6e03266d19d64f87b3333eda34e3b9936b",
-                "sha256:426ece890153ccc52cc5151a1a0ed540a5a7825414139bb4c95a868d8da54a52",
-                "sha256:491fe48adc07d13e020a8b07ef82eefc227003a046809c121bea81d3dbf1832d",
-                "sha256:4a84c7c7658dd22a33dab2e2aa2d17c18cb004a42388246f2e87cb4085ef2811",
-                "sha256:54da615e5b92c339e339fe8536cce99fe823b6ed505d4ea344852aefa1c205fb",
-                "sha256:5a7f224cdb7233182cec2a45d4c633951268d6a9bcedac37abbf79dd07012aea",
-                "sha256:61628715931f4962e0cdb2a7c87ff39eea320d2aa96bd471a3c293d146f90394",
-                "sha256:62285607a5264d1f91590abd874d6a498e229d5840669bd7d9f654cfaa599bd0",
-                "sha256:62fb881ba51dbacba9af9b779211cf9acff3442d4f2993142015b22b3cd1f92a",
-                "sha256:68428818cf80c60dc04aa0f38da20ad39b28aba4d4d199f949e7d6e04444ea86",
-                "sha256:6aaa13ee40c4552d5f3a59f543f0db6e31712cc4009ec7385407be4627259d41",
-                "sha256:70121f0ae48b25ef3e56e477b88cd0b0af0e1f3a53b5554071aa6a93ef378a03",
-                "sha256:715b34578cc740b743361f7c3e5f584b04b0f1344f45afc4e87fbac4802eb0a0",
-                "sha256:758fc8c4d6c0336e617f9f6919f9daea3ab6bb9b07005eda9a1a682e24a6cacc",
-                "sha256:7d4b8de6bb0bc736161cb0bbd95366b11b3eb24dd6b814a143d8375e75af9990",
-                "sha256:81d8d099a49f83111cce55ec03cc87eef45eec0d90f9842b4fc674f860b857b0",
-                "sha256:888d5b4b5aeed0d3449de93ea80173653e939e916cc95fe8527079e50235c1d2",
-                "sha256:95bde07d19c146d608bccb9b16e144ec8f139bcfe7fd72331858698a71c9b4f5",
-                "sha256:9bf572e4f5aa23f88dd902f10bb103cb5979022a38eec684bfa6d61851173fec",
-                "sha256:bab5a1e15b9466a25c96cda19139f3beb3e669794373b9ce28c4cf158c6e841d",
-                "sha256:bd4b1af45fd322dcd1fb2a9195b4f93f570d1a5902a842e3e6051385fac88f9c",
-                "sha256:bde677047305fe76c7ee3e4492b545e0018918e44141cc154fe39e124e433991",
-                "sha256:c389d7cc2b821853fb018c85457da3e7941db64f4387720a329bc7ff06a27963",
-                "sha256:d055ff750fcab69ca4e57b656d9c6ad33682e9b8d564f2fbe667ab95c63591b0",
-                "sha256:d53f59744b01f1440a1b0973ed2c3a7de204135c593299ee997828aad5191693",
-                "sha256:f115150cc4361dd46153302a640c7fa1804ac207f9cc356228248e351a8b4676",
-                "sha256:f1e88b30da8163215eab643962ae9d9252e47b4ea53404f2c4f10f24e70ddc62",
-                "sha256:f8191fef303025879e6c3548ecd8a95aafc0728c764ab72ec51a0bdf0c91a341"
+                "sha256:014ea143572fee1c18322b7908140ad23b3994036ef4c0d630110faf942652f8",
+                "sha256:0172423a27fbcae3751ef016663b72e1a516777de324a76e30efa170dbd3dd2d",
+                "sha256:01aa5f803db724447c1d423ed583e42bf5264c597fd55e4add4301f163b0be48",
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+                "sha256:09083c2487ca3c0865dc588e07aeaa25416da3d95f7482c07e92f47e080aa17b",
+                "sha256:0d5d862b1cfbec5028ce1ecac06a3b42bc7703eb80e4b53fceb2738724311443",
+                "sha256:14f0eb5db872c231b20c18b1e5806352723a3a89fb4254af3b3e14f22eaaec75",
+                "sha256:1e2f89d2e5e3c7a88e25a3b0e43626dba8db2aa700253023b82e630d12b37109",
+                "sha256:26155ea7a243cbf23287f390dba13d7927ffa1586d3208e0e8d615d0c506f996",
+                "sha256:2ed6343b625b16bcb63c5b10523fd15ed8934e1ed0f772c534985e9f5e73d894",
+                "sha256:34fcec18f6e4b24b4a5f6185205a04f1eab1e56f8f1d028a2a03694ebcc2ddd4",
+                "sha256:4d0e3515ef98aa4f0dc289ff2eebb0ece6260bbf37c2ea2022aad63797eacf60",
+                "sha256:5de2464c254380d8a6c20a2746614d5a436260be1507491442cf1088e59430d2",
+                "sha256:6607ae6cd3a07f8a4c3198ffbf256c261661965742e2b5265a77cd5c679c9bba",
+                "sha256:8110e6c414d3efc574543109ee618fe2c1f96fa31833a1ff36cc34e968c4f233",
+                "sha256:816de75418ea0953b5eb7b8a74933ee5a46719491cd2b16f718afc4b291a9658",
+                "sha256:861e459b0e97673af6cc5e7f597035c2e3acdfb2608132665406cded25ba64c7",
+                "sha256:87a2725ad7d41cd7376373c15fd8bf674e9c33ca56d0b8036add2d634dba372e",
+                "sha256:a006d05d9aa052657ee3e4dc92544faae5fcbaafc6128217310945610d862d39",
+                "sha256:bce28277f308db43a6b4965734366f533b3ff009571ec7ffa583cb77539b84d6",
+                "sha256:c10ff6112d119f82b1618b6dc28126798481b9355d8748b64b9b55051eb4f01b",
+                "sha256:d375d8ccd3cebae8d90270f7aa8532fe05908f79e78ae489068f3b4eee5994e8",
+                "sha256:d37843fb8df90376e9e91336724d78a32b988d3d20ab6656da4eb8ee3a45b63c",
+                "sha256:e47e257ba5934550d7235665eee6c911dc7178419b614ba9e1fbb1ce6325b14f",
+                "sha256:e98d09f487267f1e8d1179bf3b9d7709b30a916491997137dd24d6ae44d18d79",
+                "sha256:ebbb777cbf9312359b897bf81ba00dae0f5cb69fba2a18265dcc18a6f5ef7519",
+                "sha256:ee5f5188edb20a29c1cc4a039b074fdc5575337c9a68f3063449ab47757bb064",
+                "sha256:f03bd97650d2e42710fbe4cf8a59fae657f191df851fc9fc683ecef10746a375",
+                "sha256:f1149d6e5c49d069163e58a3196865e4321bad1803d7886e07d8710de392c548",
+                "sha256:f3c5c52f7cb8b84bfaaf22d82cb9e6e9a8297f7c2ed14d806a0f5e4d22e83fb7",
+                "sha256:f597a243b8550a3a0b15122b14e49d8a7e622ba1c9d29776af741f1845478d79",
+                "sha256:fc1f2a5a5963e2e73bac4926bdaf7790c4d7d77e8fc0590817880e22dd9d0b8b",
+                "sha256:fc4cddb0b474b12ed7bdce6be1b9edc65352e8ce66bc10ff8cbbfb3d4047dbf4",
+                "sha256:fcb251305fa24a490b6a9ee2180e5f8252915fb778d3dafc70f9cc3f863827b9"
             ],
             "index": "pypi",
-            "version": "==1.3.22"
+            "version": "==1.3.24"
+        },
+        "stringcase": {
+            "hashes": [
+                "sha256:48a06980661908efe8d9d34eab2b6c13aefa2163b3ced26972902e3bdfd87008"
+            ],
+            "version": "==1.2.0"
+        },
+        "typing-extensions": {
+            "hashes": [
+                "sha256:7cb407020f00f7bfc3cb3e7881628838e69d8f3fcab2f64742a5e76b2f841918",
+                "sha256:99d4073b617d30288f569d3f13d2bd7548c3a7e4c8de87db09a9d29bb3a4a60c",
+                "sha256:dafc7639cde7f1b6e1acc0f457842a83e722ccca8eef5270af2d74792619a89f"
+            ],
+            "version": "==3.7.4.3"
+        },
+        "typing-inspect": {
+            "hashes": [
+                "sha256:3b98390df4d999a28cf5b35d8b333425af5da2ece8a4ea9e98f71e7591347b4f",
+                "sha256:8f1b1dd25908dbfd81d3bebc218011531e7ab614ba6e5bf7826d887c834afab7",
+                "sha256:de08f50a22955ddec353876df7b2545994d6df08a2f45d54ac8c05e530372ca0"
+            ],
+            "version": "==0.6.0"
         }
     },
     "develop": {
@@ -184,58 +232,61 @@
         },
         "coverage": {
             "hashes": [
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+                "sha256:f11642dddbb0253cc8853254301b51390ba0081750a8ac03f20ea8103f0c56b6"
             ],
             "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3, 3.4' and python_version < '4'",
-            "version": "==5.3.1"
+            "version": "==5.5"
         },
         "docutils": {
             "hashes": [
@@ -253,19 +304,19 @@
         },
         "flake8": {
             "hashes": [
-                "sha256:749dbbd6bfd0cf1318af27bf97a14e28e5ff548ef8e5b1566ccfb25a11e7c839",
-                "sha256:aadae8761ec651813c24be05c6f7b4680857ef6afaae4651a4eccaef97ce6c3b"
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+                "sha256:78873e372b12b093da7b5e5ed302e8ad9e988b38b063b61ad937f26ca58fc5f0"
             ],
             "index": "pypi",
-            "version": "==3.8.4"
+            "version": "==3.9.0"
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         "flake8-bugbear": {
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-                "sha256:f35b8135ece7a014bc0aee5b5d485334ac30a6da48494998cc1fabf7ec70d703"
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             "index": "pypi",
-            "version": "==20.11.1"
+            "version": "==21.4.3"
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         "flake8-print": {
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@@ -276,19 +327,19 @@
         },
         "gitdb": {
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-                "sha256:91f36bfb1ab7949b3b40e23736db18231bf7593edada2ba5c3a174a7b23657ac",
-                "sha256:c9e1f2d0db7ddb9a704c2a0217be31214e91a4fe1dea1efad19ae42ba0c285c9"
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             "markers": "python_version >= '3.4'",
-            "version": "==4.0.5"
+            "version": "==4.0.7"
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         "gitpython": {
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-                "sha256:867ec3dfb126aac0f8296b19fb63b8c4a399f32b4b6fafe84c4b10af5fa9f7b5"
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-            "version": "==3.1.12"
+            "version": "==3.1.14"
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         "idna": {
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@@ -316,11 +367,11 @@
         },
         "jinja2": {
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-                "sha256:f0a4641d3cf955324a89c04f3d94663aa4d638abe8f733ecd3582848e1c37035"
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-            "version": "==2.11.2"
+            "version": "==2.11.3"
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@@ -356,8 +407,12 @@
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@@ -366,24 +421,39 @@
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             "version": "==1.1.1"
@@ -397,31 +467,39 @@
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@@ -461,11 +539,11 @@
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@@ -552,11 +630,11 @@
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@@ -568,19 +646,19 @@
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@@ -635,36 +713,53 @@
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@@ -745,11 +840,11 @@
         },
         "smmap": {
             "hashes": [
-                "sha256:54c44c197c819d5ef1991799a7e30b662d1e520f2ac75c9efbeb54a742214cf4",
-                "sha256:9c98bbd1f9786d22f14b3d4126894d56befb835ec90cef151af566c7e19b5d24"
+                "sha256:7e65386bd122d45405ddf795637b7f7d2b532e7e401d46bbe3fb49b9986d5182",
+                "sha256:a9a7479e4c572e2e775c404dcd3080c8dc49f39918c2cf74913d30c4c478e3c2"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
-            "version": "==3.0.4"
+            "markers": "python_version >= '3.5'",
+            "version": "==4.0.0"
         },
         "snapshottest": {
             "hashes": [
@@ -761,10 +856,10 @@
         },
         "snowballstemmer": {
             "hashes": [
-                "sha256:209f257d7533fdb3cb73bdbd24f436239ca3b2fa67d56f6ff88e86be08cc5ef0",
-                "sha256:df3bac3df4c2c01363f3dd2cfa78cce2840a79b9f1c2d2de9ce8d31683992f52"
+                "sha256:b51b447bea85f9968c13b650126a888aabd4cb4463fca868ec596826325dedc2",
+                "sha256:e997baa4f2e9139951b6f4c631bad912dfd3c792467e2f03d7239464af90e914"
             ],
-            "version": "==2.0.0"
+            "version": "==2.1.0"
         },
         "sphinx": {
             "hashes": [
@@ -776,11 +871,11 @@
         },
         "sphinx-rtd-theme": {
             "hashes": [
-                "sha256:eda689eda0c7301a80cf122dad28b1861e5605cbf455558f3775e1e8200e83a5",
-                "sha256:fa6bebd5ab9a73da8e102509a86f3fcc36dec04a0b52ea80e5a033b2aba00113"
+                "sha256:32bd3b5d13dc8186d7a42fc816a23d32e83a4827d7d9882948e7b837c232da5a",
+                "sha256:4a05bdbe8b1446d77a01e20a23ebc6777c74f43237035e76be89699308987d6f"
             ],
             "index": "pypi",
-            "version": "==0.5.1"
+            "version": "==0.5.2"
         },
         "sphinxcontrib-serializinghtml": {
             "hashes": [
@@ -874,23 +969,29 @@
         },
         "urllib3": {
             "hashes": [
-                "sha256:19188f96923873c92ccb987120ec4acaa12f0461fa9ce5d3d0772bc965a39e08",
-                "sha256:d8ff90d979214d7b4f8ce956e80f4028fc6860e4431f731ea4a8c08f23f99473"
+                "sha256:2f4da4594db7e1e110a944bb1b551fdf4e6c136ad42e4234131391e21eb5b0df",
+                "sha256:e7b021f7241115872f92f43c6508082facffbd1c048e3c6e2bb9c2a157e28937"
             ],
             "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3, 3.4' and python_version < '4'",
-            "version": "==1.26.2"
+            "version": "==1.26.4"
         },
         "wasmer": {
             "hashes": [
-                "sha256:519d9f7a33f0dc28498edf8d074944df1cfda3f4d56a6b0a9dc606e99f230c07",
-                "sha256:6e37fd76931da954d12f7708e7fc790c479e17ea6dfe54bb4f1403d6fe919c62",
-                "sha256:92aee4b3994735f72e27c9deaca36d063781ddfd1068756bf63509288c1a2c14",
-                "sha256:c36c6c7a3582c0467ea76c5b86a5a25c2e1a713669ebf8fc6511b26f30828ed7",
-                "sha256:d5a58b318628bd48605a4810ee9ba030ec4423dee730d45f031bd082cf36ad8b",
-                "sha256:f864b1e910e6803aa8f3ed9c371b145f0b6fd191f5fbefea011ac7ed4258734d",
-                "sha256:fa1c8479781c91e6b814ef006f6e099b6550eba12601a8617475fb514fc09365"
-            ],
-            "version": "==0.4.1"
+                "sha256:04e5d51eed336be0e1bf1445aa032fc34466b77220c26732b8990df872f29e92",
+                "sha256:0d755a93184380f9785e1f8269b070f4a4a3285ae0f7f9571cfaf2ea215b102d",
+                "sha256:11e73026cb7e9a948b86324bd573cafe4d7be91f65ff45b1dc67485044348754",
+                "sha256:15b355fed4ebe9d912a7fe236391aac591cc64c7647e14e517c2a6f451a83914",
+                "sha256:1fada13fb536f44e12d7c98c557f5b7a55df94389d3cb90964193dcc8e16f0fa",
+                "sha256:427e9c5e5301a453a09b8b9ceb8c793d85411b8f45e54c9c0d801566dd8d214e",
+                "sha256:690c5ed46a98e91bc638f52a25e5011c5baa1ef0581f414018eb7aa0e7f844bc",
+                "sha256:6b41046db73facc064cb9649627d9cdd1b88ada74e745134e44e09ada6827056",
+                "sha256:8b13214b5dcc84d43f4c44e2309442497f19137561afada7f34babad89365355",
+                "sha256:a08be93aff695ce3be871994f726716b68bef36bd583bccad75778359cd273df",
+                "sha256:d77b169079183c131d398c57dfc36e5cc4b34ae2543878ac2056e858f040c099",
+                "sha256:dd6c5ab2c41e9fd31442483ac7adc81d886cc3242d604dc3c895df257aa7dbe2",
+                "sha256:e2ecd788140468d2d489fc92537b47e2baf4ffdec00fe41f055715d261e4988b"
+            ],
+            "version": "==1.0.0"
         },
         "wcwidth": {
             "hashes": [
diff --git a/graphql_compiler/compiler/compiler_frontend.py b/graphql_compiler/compiler/compiler_frontend.py
index 185ceece0..4e4aff06b 100644
--- a/graphql_compiler/compiler/compiler_frontend.py
+++ b/graphql_compiler/compiler/compiler_frontend.py
@@ -62,6 +62,7 @@
 from dataclasses import dataclass
 from typing import Dict, List, Optional
 
+from dataclasses_json import DataClassJsonMixin
 from graphql import (
     DocumentNode,
     GraphQLInt,
@@ -133,7 +134,18 @@
 from .validation import validate_schema_and_query_ast
 
 
-@dataclass(frozen=True)
+@dataclass(init=True, repr=True, eq=True, frozen=True)
+class ProviderMetadata(DataClassJsonMixin):
+    """Metadata about the provider."""
+
+    # Name of the type of provider (ex. PostgreSQL, Cypher, etc).
+    backend_type: str
+
+    # Whether this backend requires MSSQL fold postprocessing for folded outputs.
+    requires_fold_postprocessing: bool
+
+
+@dataclass(init=True, repr=True, eq=False, frozen=True)
 class OutputMetadata:
     """Metadata about a query's outputs."""
 
@@ -148,6 +160,9 @@ class OutputMetadata:
     # in which case the type must be GraphQLInt.
     folded: bool
 
+    # Provider metadata.
+    provider_metadata: Optional[ProviderMetadata] = None
+
     def __eq__(self, other):
         """Check another OutputMetadata object for equality against this one."""
         # Unfortunately, GraphQL types don't have an equality operator defined,
@@ -156,6 +171,7 @@ def __eq__(self, other):
             is_same_type(self.type, other.type)
             and self.optional == other.optional
             and self.folded == other.folded
+            and self.provider_metadata == other.provider_metadata
         )
 
     def __ne__(self, other):
diff --git a/graphql_compiler/query_planning_and_execution/__init__.py b/graphql_compiler/query_planning_and_execution/__init__.py
new file mode 100644
index 000000000..267b30955
--- /dev/null
+++ b/graphql_compiler/query_planning_and_execution/__init__.py
@@ -0,0 +1 @@
+# Copyright 2021-present Kensho Technologies, LLC.
diff --git a/graphql_compiler/schema_transformation/make_query_plan.py b/graphql_compiler/query_planning_and_execution/make_query_plan.py
similarity index 99%
rename from graphql_compiler/schema_transformation/make_query_plan.py
rename to graphql_compiler/query_planning_and_execution/make_query_plan.py
index 6547b08f2..3cc53ecdc 100644
--- a/graphql_compiler/schema_transformation/make_query_plan.py
+++ b/graphql_compiler/query_planning_and_execution/make_query_plan.py
@@ -21,7 +21,7 @@
 from ..ast_manipulation import get_only_query_definition
 from ..exceptions import GraphQLValidationError
 from ..schema import FilterDirective, OutputDirective
-from .split_query import AstType, SubQueryNode
+from ..schema_transformation.split_query import AstType, SubQueryNode
 
 
 @dataclass
diff --git a/graphql_compiler/query_planning_and_execution/sync_query_execution.py b/graphql_compiler/query_planning_and_execution/sync_query_execution.py
new file mode 100644
index 000000000..b9af2f666
--- /dev/null
+++ b/graphql_compiler/query_planning_and_execution/sync_query_execution.py
@@ -0,0 +1,35 @@
+# Copyright 2021-present Kensho Technologies, LLC.
+from typing import Any, Callable, ContextManager, Dict, Iterable, Mapping
+
+from ..post_processing.sql_post_processing import post_process_mssql_folds
+from ..query_formatting.common import deserialize_multiple_arguments
+from .typedefs import QueryExecutionFunc, SimpleExecute
+
+
+def _execute_simple_execute_node(
+    provider_client_makers: Dict[str, Callable[[], ContextManager[QueryExecutionFunc]]],
+    query_plan_node: SimpleExecute,
+) -> Iterable[Mapping[str, Any]]:
+    """Execute a SimpleExecute."""
+    provider_client_maker = provider_client_makers[query_plan_node.provider_id]
+    arguments = deserialize_multiple_arguments(
+        query_plan_node.arguments, query_plan_node.input_metadata
+    )
+
+    with provider_client_maker() as query_client:
+        result = query_client(query_plan_node.query, query_plan_node.input_metadata, arguments)
+        # Apply post processing for MSSQL folds if applicable.
+        requires_postprocessing = False
+        for _, output_metadata in query_plan_node.output_metadata.items():
+            if (
+                output_metadata.provider_metadata is not None
+                and output_metadata.provider_metadata.requires_fold_postprocessing
+            ):
+                requires_postprocessing = True
+        if requires_postprocessing:
+            list_dict_result = [dict(entry) for entry in result]
+            post_process_mssql_folds(list_dict_result, query_plan_node.output_metadata)
+            return list_dict_result
+
+        # Otherwise, return result as is.
+        return result
diff --git a/graphql_compiler/query_planning_and_execution/typedefs.py b/graphql_compiler/query_planning_and_execution/typedefs.py
new file mode 100644
index 000000000..d46aec8b8
--- /dev/null
+++ b/graphql_compiler/query_planning_and_execution/typedefs.py
@@ -0,0 +1,251 @@
+# Copyright 2021-present Kensho Technologies, LLC.
+from abc import ABCMeta
+import copy
+from dataclasses import dataclass, field
+from typing import Any, Callable, Dict, Iterable, Mapping, Optional
+
+from dataclasses_json import DataClassJsonMixin, config
+from graphql import (
+    GraphQLList,
+    GraphQLNonNull,
+    GraphQLType,
+    ListTypeNode,
+    NamedTypeNode,
+    NonNullTypeNode,
+    TypeNode,
+    parse_type,
+    specified_scalar_types,
+)
+
+from .. import GraphQLDate, GraphQLDateTime, GraphQLDecimal
+from ..compiler.compiler_frontend import OutputMetadata, ProviderMetadata
+from ..global_utils import is_same_type
+
+
+QueryExecutionFunc = Callable[
+    [str, Dict[str, GraphQLType], Dict[str, Any]], Iterable[Mapping[str, Any]]
+]
+
+# Custom scalar types.
+CUSTOM_SCALAR_TYPES = {
+    GraphQLDate.name: GraphQLDate,
+    GraphQLDateTime.name: GraphQLDateTime,
+    GraphQLDecimal.name: GraphQLDecimal,
+}
+
+# Custom scalar types must not have name conflicts with builtin scalar types.
+if set(CUSTOM_SCALAR_TYPES).intersection(specified_scalar_types):
+    raise AssertionError(
+        f"Custom scalar types must have different names than builtin scalar types. Received "
+        f"overlapping type(s) {set(CUSTOM_SCALAR_TYPES).intersection(specified_scalar_types)}. "
+        f"Custom scalar types: {set(CUSTOM_SCALAR_TYPES)}. Builtin scalar types: "
+        f"{set(specified_scalar_types)}."
+    )
+
+# Custom scalar types combined with builtin scalar types represent all allowable scalar types.
+ALL_SCALAR_TYPES = copy.copy(CUSTOM_SCALAR_TYPES)
+ALL_SCALAR_TYPES.update(specified_scalar_types)
+
+
+def _type_from_scalar_type_dictionary(
+    scalar_types: Dict[str, GraphQLType], type_node: TypeNode
+) -> GraphQLType:
+    """Get the GraphQL type definition from an AST node.
+
+    Given a scalar type dictionary and an AST node describing a type, return a GraphQLType
+    definition, which applies to that type. For example, if provided the parsed AST node for
+    `[Date]`, a GraphQLList instance will be returned, containing the type called
+    "Date" found in the scalar type dictionary. If a type called "Date" is not found in the scalar
+    type dictionary, then None will be returned.
+
+    Note: this is very similar to GraphQL's type_from_ast. However, instead of requiring a GraphQL
+    schema this function requires a dictionary of the scalar types. This simplifies deserialization
+    and allows for custom scalar types without constructing an entire schema.
+
+    Args:
+        scalar_types: dictionary mapping type name to GraphQLType
+        type_node: AST node describing a type
+
+    Returns:
+        GraphQLType that applies to the type specified in type_node.
+
+    Raises:
+        AssertionError: if an invalid type node is given.
+    """
+    if isinstance(type_node, ListTypeNode):
+        inner_type = _type_from_scalar_type_dictionary(scalar_types, type_node.type)
+        if inner_type:
+            return GraphQLList(inner_type)
+        else:
+            raise AssertionError(
+                f"Invalid type node. ListTypeNode contained inner type {inner_type}."
+            )
+    elif isinstance(type_node, NonNullTypeNode):
+        inner_type = _type_from_scalar_type_dictionary(scalar_types, type_node.type)
+        if inner_type:
+            return GraphQLNonNull(inner_type)
+        else:
+            raise AssertionError(
+                f"Invalid type node. NonNullTypeNone contained inner type {inner_type}."
+            )
+    elif isinstance(type_node, NamedTypeNode):
+        return scalar_types[type_node.name.value]
+
+    # Not reachable. All possible type nodes have been considered.
+    raise AssertionError(f"Unexpected type node: {type_node}.")
+
+
+def _serialize_output_metadata_field(
+    output_metadata_dictionary: Optional[Dict[str, "OutputMetadata"]]
+) -> Optional[Dict[str, Dict[str, Any]]]:
+    """Serialize OutputMetadata into a dictionary."""
+    if not output_metadata_dictionary:
+        return None
+    dictionary_value = {}
+    for output_name, output_metadata in output_metadata_dictionary.items():
+        dictionary_value[output_name] = {
+            "graphql_type": str(output_metadata["graphql_type"]),
+            "optional": output_metadata["optional"],
+            "folded": output_metadata["folded"],
+            "provider_metadata": output_metadata["provider_metadata"],
+        }
+    return dictionary_value
+
+
+def _deserialize_output_metadata_field(
+    dict_value: Optional[Dict[str, Dict[str, Any]]]
+) -> Optional[Dict[str, "OutputMetadata"]]:
+    """Deserialize the dictionary representation of OutputMetadata."""
+    if not dict_value:
+        return None
+    output_metadata_dictionary = {}
+    for output_name, output_metadata in dict_value.items():
+        output_metadata_dictionary[output_name] = OutputMetadata(
+            type=_type_from_scalar_type_dictionary(
+                ALL_SCALAR_TYPES, parse_type(output_metadata["graphql_type"])
+            ),
+            optional=output_metadata["optional"],
+            folded=output_metadata["folded"],
+            provider_metadata=ProviderMetadata(
+                backend_type=output_metadata["provider_metadata"]["backend_type"],
+                requires_fold_postprocessing=output_metadata["provider_metadata"][
+                    "requires_fold_postprocessing"
+                ],
+            ),
+        )
+    return output_metadata_dictionary
+
+
+def _serialize_input_metadata_field(
+    input_metadata_dictionary: Optional[Dict[str, Any]]
+) -> Optional[Dict[str, str]]:
+    """Serialize input metadata, converting GraphQLTypes to strings."""
+    # It is possible to have an empty input metadata dictionary (i.e. no inputs for the query).
+    # Note that this is different than "None", which means no metadata was provided.
+    if input_metadata_dictionary == {}:
+        return {}
+    if not input_metadata_dictionary:
+        return None
+    dictionary_value = {}
+    for input_name, input_type in input_metadata_dictionary.items():
+        dictionary_value[input_name] = str(input_type)
+    return dictionary_value
+
+
+def _deserialize_input_metadata_field(
+    dict_value: Optional[Dict[str, str]]
+) -> Optional[Dict[str, GraphQLType]]:
+    """Deserialize input metadata, converting strings to GraphQLTypes."""
+    # It is possible to have an empty input metadata dictionary (i.e. no inputs for the query).
+    # Note that this is different than "None", which means no metadata was provided.
+    if dict_value == {}:
+        return {}
+    if not dict_value:
+        return None
+    input_metadata_dictionary = {}
+    for input_name, input_type in dict_value.items():
+        input_metadata_dictionary[input_name] = _type_from_scalar_type_dictionary(
+            ALL_SCALAR_TYPES, parse_type(input_type)
+        )
+    return input_metadata_dictionary
+
+
+def _compare_input_metadata_field(
+    left_input_metadata: Optional[Dict[str, GraphQLType]],
+    right_input_metadata: Optional[Dict[str, GraphQLType]],
+) -> bool:
+    """Check input_metadata SimpleExecute field equality, comparing GraphQLTypes appropriately."""
+    if left_input_metadata is None:
+        # Since left_input_metadata is None, checking for equality requires determining whether or
+        # not right_metadata is also None. If right_metadata is None, left and right metadata
+        # are equal and True is returned.
+        return right_input_metadata is None
+
+    # right_input_metadata is None, but left_input_metadata is not.
+    if right_input_metadata is None:
+        return False
+
+    # Neither left_input_metadata nor right_input_metadata is None.
+    input_metadata_keys = left_input_metadata.keys()
+
+    # Check if input_metadata keys match.
+    if input_metadata_keys != right_input_metadata.keys():
+        return False
+    # Check if input_metadata values match for all keys.
+    for key in input_metadata_keys:
+        if not is_same_type(left_input_metadata[key], right_input_metadata[key]):
+            return False
+
+    # All keys and values match so return True.
+    return True
+
+
+# ############
+# Public API #
+# ############
+
+
+@dataclass(init=True, repr=True, eq=True, frozen=True)
+class QueryPlanNode(DataClassJsonMixin, metaclass=ABCMeta):
+    """Abstract query plan node. May or may not contain other nodes, depending on its type."""
+
+    # Unique ID of the plan node.
+    # Note: do not compare "uuid" values to determine whether query plan nodes are equal, since two
+    # plans with different identifiers might still be semantically equivalent and therefore equal.
+    uuid: str = field(compare=False)
+
+
+@dataclass(init=True, repr=True, eq=False, frozen=True)
+class SimpleExecute(QueryPlanNode):
+    """Just give the specified query and args to the provider, it'll execute it for you as-is."""
+
+    provider_id: str
+    query: str  # in whatever query language the provider will accept (not necessarily GraphQL)
+    arguments: Dict[str, Any]
+
+    # Input and output metadata of the query.
+    output_metadata: Dict[str, OutputMetadata] = field(
+        metadata=config(
+            encoder=_serialize_output_metadata_field, decoder=_deserialize_output_metadata_field
+        )
+    )
+    input_metadata: Dict[str, GraphQLType] = field(
+        metadata=config(
+            encoder=_serialize_input_metadata_field, decoder=_deserialize_input_metadata_field
+        )
+    )
+
+    def __eq__(self, other: Any) -> bool:
+        """Check equality between an object and this SimpleExecute."""
+        if not isinstance(other, SimpleExecute):
+            return False
+
+        # Perform special check for input_metadata since GraphQLTypes don't have equality, and
+        # check all other fields in a straight forward manner.
+        return (
+            self.provider_id == other.provider_id
+            and self.query == other.query
+            and self.arguments == other.arguments
+            and self.output_metadata == other.output_metadata
+            and _compare_input_metadata_field(self.input_metadata, other.input_metadata)
+        )
diff --git a/graphql_compiler/tests/schema_transformation_tests/test_make_query_plan.py b/graphql_compiler/tests/schema_transformation_tests/test_make_query_plan.py
index eb825fc90..997995d5c 100644
--- a/graphql_compiler/tests/schema_transformation_tests/test_make_query_plan.py
+++ b/graphql_compiler/tests/schema_transformation_tests/test_make_query_plan.py
@@ -4,7 +4,7 @@
 
 from graphql import parse, print_ast
 
-from ...schema_transformation.make_query_plan import make_query_plan
+from ...query_planning_and_execution.make_query_plan import make_query_plan
 from ...schema_transformation.split_query import split_query
 from .example_schema import basic_merged_schema
 
diff --git a/setup.py b/setup.py
index 26e84f88a..f5d372058 100755
--- a/setup.py
+++ b/setup.py
@@ -56,10 +56,10 @@ def find_long_description() -> str:
     packages=find_packages(exclude=["tests*"]),
     install_requires=[  # Make sure to keep in sync with Pipfile requirements.
         "ciso8601>=2.1.3,<3",
-        "funcy>=1.7.3,<2",
+        "dataclasses-json>=0.5.2,<0.6" "funcy>=1.7.3,<2",
         "graphql-core>=3.1.2,<3.2",
         "six>=1.10.0",
-        "sqlalchemy>=1.3.0,<2",
+        "sqlalchemy>=1.3.0,<1.4",
     ],
     extras_require={
         ':python_version<"3.7"': ["dataclasses>=0.7,<1"],

From 0b0442964c18f4415749f9b21abcd407a1b1f73a Mon Sep 17 00:00:00 2001
From: Selene Chew <selene.chew@kensho.com>
Date: Fri, 16 Apr 2021 12:27:18 -0400
Subject: [PATCH 2/5] generate_query_plan implementation

---
 .../compiler/compiler_frontend.py             |  16 --
 .../make_query_plan.py                        | 228 ++++++++++++++----
 .../sync_query_execution.py                   |   9 +-
 .../query_planning_and_execution/typedefs.py  |  84 +++++--
 graphql_compiler/schema/schema_info.py        | 102 ++++----
 graphql_compiler/schema/typedefs.py           |   2 +-
 .../test_sqlalchemy_schema_generation.py      |  33 +++
 7 files changed, 336 insertions(+), 138 deletions(-)

diff --git a/graphql_compiler/compiler/compiler_frontend.py b/graphql_compiler/compiler/compiler_frontend.py
index 4e4aff06b..3d84b8e39 100644
--- a/graphql_compiler/compiler/compiler_frontend.py
+++ b/graphql_compiler/compiler/compiler_frontend.py
@@ -62,7 +62,6 @@
 from dataclasses import dataclass
 from typing import Dict, List, Optional
 
-from dataclasses_json import DataClassJsonMixin
 from graphql import (
     DocumentNode,
     GraphQLInt,
@@ -134,17 +133,6 @@
 from .validation import validate_schema_and_query_ast
 
 
-@dataclass(init=True, repr=True, eq=True, frozen=True)
-class ProviderMetadata(DataClassJsonMixin):
-    """Metadata about the provider."""
-
-    # Name of the type of provider (ex. PostgreSQL, Cypher, etc).
-    backend_type: str
-
-    # Whether this backend requires MSSQL fold postprocessing for folded outputs.
-    requires_fold_postprocessing: bool
-
-
 @dataclass(init=True, repr=True, eq=False, frozen=True)
 class OutputMetadata:
     """Metadata about a query's outputs."""
@@ -160,9 +148,6 @@ class OutputMetadata:
     # in which case the type must be GraphQLInt.
     folded: bool
 
-    # Provider metadata.
-    provider_metadata: Optional[ProviderMetadata] = None
-
     def __eq__(self, other):
         """Check another OutputMetadata object for equality against this one."""
         # Unfortunately, GraphQL types don't have an equality operator defined,
@@ -171,7 +156,6 @@ def __eq__(self, other):
             is_same_type(self.type, other.type)
             and self.optional == other.optional
             and self.folded == other.folded
-            and self.provider_metadata == other.provider_metadata
         )
 
     def __ne__(self, other):
diff --git a/graphql_compiler/query_planning_and_execution/make_query_plan.py b/graphql_compiler/query_planning_and_execution/make_query_plan.py
index 3cc53ecdc..d2e60be9e 100644
--- a/graphql_compiler/query_planning_and_execution/make_query_plan.py
+++ b/graphql_compiler/query_planning_and_execution/make_query_plan.py
@@ -1,7 +1,8 @@
 # Copyright 2019-present Kensho Technologies, LLC.
 from copy import copy
 from dataclasses import dataclass
-from typing import FrozenSet, List, Optional, Tuple, cast
+from typing import FrozenSet, List, Optional, Tuple, Union, cast
+from uuid import uuid4
 
 from graphql import print_ast
 from graphql.language.ast import (
@@ -17,11 +18,25 @@
     StringValueNode,
 )
 from graphql.pyutils import FrozenList
+from sqlalchemy.dialects.mssql.base import MSDialect
 
 from ..ast_manipulation import get_only_query_definition
+from ..compiler.common import (
+    CYPHER_LANGUAGE,
+    GREMLIN_LANGUAGE,
+    MATCH_LANGUAGE,
+    compile_graphql_to_cypher,
+    compile_graphql_to_gremlin,
+    compile_graphql_to_match,
+    compile_graphql_to_sql,
+)
+from ..compiler.sqlalchemy_extensions import print_sqlalchemy_query_string
 from ..exceptions import GraphQLValidationError
+from ..global_utils import QueryStringWithParameters
 from ..schema import FilterDirective, OutputDirective
+from ..schema.schema_info import CommonSchemaInfo, SQLAlchemySchemaInfo
 from ..schema_transformation.split_query import AstType, SubQueryNode
+from .typedefs import ProviderMetadata, QueryPlan, SimpleExecute
 
 
 @dataclass
@@ -66,44 +81,65 @@ class QueryPlanDescriptor:
     output_join_descriptors: List[OutputJoinDescriptor]
 
 
-def make_query_plan(
-    root_sub_query_node: SubQueryNode, intermediate_output_names: FrozenSet[str]
-) -> QueryPlanDescriptor:
-    """Return a QueryPlanDescriptor, whose query ASTs have @filters added.
-
-    For each parent of parent and child SubQueryNodes, a new @filter directive will be added
-    in the child AST. It will be added on the field whose @output directive has the out_name
-    equal to the child's out name as specified in the QueryConnection. The newly added @filter
-    will be a 'in_collection' type filter, and the name of the local variable is guaranteed to
-    be the same as the out_name of the @output on the parent.
-
-    ASTs contained in the input node and its children nodes will not be modified.
+def _make_simple_execute_node(
+    query_and_parameters: QueryStringWithParameters,
+    schema_info: Union[CommonSchemaInfo, SQLAlchemySchemaInfo],
+    provider_id: str,
+    backend_type: Optional[str],
+) -> SimpleExecute:
+    """Generate a SimpleExecuteNode.
 
     Args:
-        root_sub_query_node: representing the base of a query split into pieces
-                             that we want to turn into a query plan.
-        intermediate_output_names: names of outputs to be removed at the end.
+        query_and_parameters: the query and parameters for which to create a SimpleExecute.
+        schema_info: schema information to use for query compilation.
+        provider_id: the identifier of the provider to be queried.
+        backend_type: the backend type. Note: this is inferred from the SQLAlchemySchemaInfo's
+                      dialect for SQL backends.
 
     Returns:
-        QueryPlanDescriptor containing a tree of SubQueryPlans that wrap around each individual
-        query AST, the set of intermediate output names that are to be removed at the end, and
-        information on which outputs are to be connect to which in what manner.
-    """
-    output_join_descriptors: List[OutputJoinDescriptor] = []
+        SimpleExecute with all necessary information to execute the given query_and_parameters.
 
-    root_sub_query_plan = SubQueryPlan(
-        query_ast=root_sub_query_node.query_ast,
-        schema_id=root_sub_query_node.schema_id,
-        parent_query_plan=None,
-        child_query_plans=[],
-    )
-
-    _make_query_plan_recursive(root_sub_query_node, root_sub_query_plan, output_join_descriptors)
+    """
+    if isinstance(schema_info, SQLAlchemySchemaInfo):
+        # Compiled SQL query.
+        compilation_result = compile_graphql_to_sql(schema_info, query_and_parameters.query_string)
+        query = print_sqlalchemy_query_string(compilation_result.query, schema_info.dialect)
+
+        provider_metadata = ProviderMetadata(
+            backend_type=schema_info.dialect.name,
+            requires_fold_postprocessing=isinstance(schema_info.dialect, MSDialect),
+        )
+    else:
+        if backend_type == CYPHER_LANGUAGE:
+            compilation_result = compile_graphql_to_cypher(
+                schema_info, query_and_parameters.query_string
+            )
+        elif backend_type == GREMLIN_LANGUAGE:
+            compilation_result = compile_graphql_to_gremlin(
+                schema_info, query_and_parameters.query_string
+            )
+        elif backend_type == MATCH_LANGUAGE:
+            compilation_result = compile_graphql_to_match(
+                schema_info, query_and_parameters.query_string
+            )
+        # TODO: add InterpreterAdapter based backends
+        else:
+            raise AssertionError(f"Unknown non-SQL backend_type {backend_type}.")
+        # Extract the query and create provider_metadata (process is the same across Cypher,
+        # Gremlin, and Match backends)
+        query = compilation_result.query
+        provider_metadata = ProviderMetadata(
+            backend_type=backend_type, requires_fold_postprocessing=False
+        )
 
-    return QueryPlanDescriptor(
-        root_sub_query_plan=root_sub_query_plan,
-        intermediate_output_names=intermediate_output_names,
-        output_join_descriptors=output_join_descriptors,
+    return SimpleExecute(
+        str(uuid4()),
+        provider_id,
+        provider_metadata,
+        query,
+        query_and_parameters.parameters,
+        compilation_result.output_metadata,
+        compilation_result.input_metadata,
     )
 
 
@@ -291,6 +327,118 @@ def _get_in_collection_filter_directive(input_filter_name: str) -> DirectiveNode
     )
 
 
+def _get_plan_and_depth_in_dfs_order(query_plan: SubQueryPlan) -> List[Tuple[SubQueryPlan, int]]:
+    """Return a list of topologically sorted (query plan, depth) tuples."""
+
+    def _get_plan_and_depth_in_dfs_order_helper(
+        query_plan: SubQueryPlan, depth: int
+    ) -> List[Tuple[SubQueryPlan, int]]:
+        plan_and_depth_in_dfs_order = [(query_plan, depth)]
+        for child_query_plan in query_plan.child_query_plans:
+            plan_and_depth_in_dfs_order.extend(
+                _get_plan_and_depth_in_dfs_order_helper(child_query_plan, depth + 1)
+            )
+        return plan_and_depth_in_dfs_order
+
+    return _get_plan_and_depth_in_dfs_order_helper(query_plan, 0)
+
+
+######
+# Public API
+######
+
+
+def generate_query_plan(
+    query_and_parameters: QueryStringWithParameters,
+    provider_id: str,
+    *,
+    desired_page_size: Optional[int] = 5000,
+) -> QueryPlan:
+    """Generate a query plan for query_and_parameters targeting data source 'provider_id'.
+
+    Note: this functionality is intended to replace make_query_plan below. TODO(selene)
+
+    Args:
+        query_and_parameters: the query and parameters for which to create a QueryPlan.
+        provider_id: the identifier of the provider to be queried.
+        desired_page_size: target page size. None indicates that pagination should be disabled.
+                           The benefit of pagination with this sync executor is that:
+                           - You can receive results as they arrive (see execute_query_plan)
+                           - The load on the database is more controlled, and timeouts are
+                             less likely.
+                           The desired_page_size is fulfilled on a best-effort basis; setting
+                           a particular desired_page_size does not guarantee pages of precisely
+                           that size. Setting desired_page_size to a number less than 1000 is
+                           not recommended, since the server is unlikely to have sufficiently
+                           granular statistics to accomplish that, and the client is more likely
+                           to fetch many entirely empty pages. Note: this is not currently used,
+                           but will be in the near future! TODO(selene): implement ParallelPaginated
+
+    Returns:
+        QueryPlan for the given query_and_parameters against the data source specified
+        by the provider_id.
+
+    """
+    # TODO: look up schema_info and backend_type by provider_id
+    schema_info = None
+    backend_type = None
+    query_plan_node = _make_simple_execute_node(
+        query_and_parameters, schema_info, provider_id, backend_type
+    )
+
+    version = 1
+    return QueryPlan(
+        version,
+        provider_id,
+        query_and_parameters.query_string,
+        query_and_parameters.parameters,
+        desired_page_size,
+        query_plan_node.output_metadata,
+        query_plan_node,
+    )
+
+
+def make_query_plan(
+    root_sub_query_node: SubQueryNode, intermediate_output_names: FrozenSet[str]
+) -> QueryPlanDescriptor:
+    """Return a QueryPlanDescriptor, whose query ASTs have @filters added.
+
+    For each parent of parent and child SubQueryNodes, a new @filter directive will be added
+    in the child AST. It will be added on the field whose @output directive has the out_name
+    equal to the child's out name as specified in the QueryConnection. The newly added @filter
+    will be a 'in_collection' type filter, and the name of the local variable is guaranteed to
+    be the same as the out_name of the @output on the parent.
+
+    ASTs contained in the input node and its children nodes will not be modified.
+
+    Args:
+        root_sub_query_node: representing the base of a query split into pieces
+                             that we want to turn into a query plan.
+        intermediate_output_names: names of outputs to be removed at the end.
+
+    Returns:
+        QueryPlanDescriptor containing a tree of SubQueryPlans that wrap around each individual
+        query AST, the set of intermediate output names that are to be removed at the end, and
+        information on which outputs are to be connect to which in what manner.
+    """
+    output_join_descriptors: List[OutputJoinDescriptor] = []
+
+    root_sub_query_plan = SubQueryPlan(
+        query_ast=root_sub_query_node.query_ast,
+        schema_id=root_sub_query_node.schema_id,
+        parent_query_plan=None,
+        child_query_plans=[],
+    )
+
+    _make_query_plan_recursive(root_sub_query_node, root_sub_query_plan, output_join_descriptors)
+
+    return QueryPlanDescriptor(
+        root_sub_query_plan=root_sub_query_plan,
+        intermediate_output_names=intermediate_output_names,
+        output_join_descriptors=output_join_descriptors,
+    )
+
+
 def print_query_plan(query_plan_descriptor: QueryPlanDescriptor, indentation_depth: int = 4) -> str:
     """Return a string describing query plan."""
     query_plan_strings = [""]
@@ -311,17 +459,3 @@ def print_query_plan(query_plan_descriptor: QueryPlanDescriptor, indentation_dep
     query_plan_strings.append(str(query_plan_descriptor.intermediate_output_names) + "\n")
 
     return "".join(query_plan_strings)
-
-
-def _get_plan_and_depth_in_dfs_order(query_plan: SubQueryPlan) -> List[Tuple[SubQueryPlan, int]]:
-    """Return a list of topologically sorted (query plan, depth) tuples."""
-
-    def _get_plan_and_depth_in_dfs_order_helper(query_plan, depth):
-        plan_and_depth_in_dfs_order = [(query_plan, depth)]
-        for child_query_plan in query_plan.child_query_plans:
-            plan_and_depth_in_dfs_order.extend(
-                _get_plan_and_depth_in_dfs_order_helper(child_query_plan, depth + 1)
-            )
-        return plan_and_depth_in_dfs_order
-
-    return _get_plan_and_depth_in_dfs_order_helper(query_plan, 0)
diff --git a/graphql_compiler/query_planning_and_execution/sync_query_execution.py b/graphql_compiler/query_planning_and_execution/sync_query_execution.py
index b9af2f666..13de793a7 100644
--- a/graphql_compiler/query_planning_and_execution/sync_query_execution.py
+++ b/graphql_compiler/query_planning_and_execution/sync_query_execution.py
@@ -15,17 +15,12 @@ def _execute_simple_execute_node(
     arguments = deserialize_multiple_arguments(
         query_plan_node.arguments, query_plan_node.input_metadata
     )
+    requires_postprocessing = query_plan_node.provider_metadata.requires_fold_postprocessing
 
     with provider_client_maker() as query_client:
         result = query_client(query_plan_node.query, query_plan_node.input_metadata, arguments)
+
         # Apply post processing for MSSQL folds if applicable.
-        requires_postprocessing = False
-        for _, output_metadata in query_plan_node.output_metadata.items():
-            if (
-                output_metadata.provider_metadata is not None
-                and output_metadata.provider_metadata.requires_fold_postprocessing
-            ):
-                requires_postprocessing = True
         if requires_postprocessing:
             list_dict_result = [dict(entry) for entry in result]
             post_process_mssql_folds(list_dict_result, query_plan_node.output_metadata)
diff --git a/graphql_compiler/query_planning_and_execution/typedefs.py b/graphql_compiler/query_planning_and_execution/typedefs.py
index d46aec8b8..30a964308 100644
--- a/graphql_compiler/query_planning_and_execution/typedefs.py
+++ b/graphql_compiler/query_planning_and_execution/typedefs.py
@@ -8,6 +8,7 @@
 from graphql import (
     GraphQLList,
     GraphQLNonNull,
+    GraphQLScalarType,
     GraphQLType,
     ListTypeNode,
     NamedTypeNode,
@@ -18,12 +19,13 @@
 )
 
 from .. import GraphQLDate, GraphQLDateTime, GraphQLDecimal
-from ..compiler.compiler_frontend import OutputMetadata, ProviderMetadata
+from ..compiler.compiler_frontend import OutputMetadata
 from ..global_utils import is_same_type
+from ..typedefs import QueryArgumentGraphQLType
 
 
 QueryExecutionFunc = Callable[
-    [str, Dict[str, GraphQLType], Dict[str, Any]], Iterable[Mapping[str, Any]]
+    [str, Dict[str, QueryArgumentGraphQLType], Dict[str, Any]], Iterable[Mapping[str, Any]]
 ]
 
 # Custom scalar types.
@@ -48,7 +50,7 @@
 
 
 def _type_from_scalar_type_dictionary(
-    scalar_types: Dict[str, GraphQLType], type_node: TypeNode
+    scalar_types: Dict[str, GraphQLScalarType], type_node: TypeNode
 ) -> GraphQLType:
     """Get the GraphQL type definition from an AST node.
 
@@ -63,7 +65,7 @@ def _type_from_scalar_type_dictionary(
     and allows for custom scalar types without constructing an entire schema.
 
     Args:
-        scalar_types: dictionary mapping type name to GraphQLType
+        scalar_types: dictionary mapping type name to GraphQLScalarType
         type_node: AST node describing a type
 
     Returns:
@@ -96,7 +98,7 @@ def _type_from_scalar_type_dictionary(
 
 
 def _serialize_output_metadata_field(
-    output_metadata_dictionary: Optional[Dict[str, "OutputMetadata"]]
+    output_metadata_dictionary: Optional[Dict[str, OutputMetadata]]
 ) -> Optional[Dict[str, Dict[str, Any]]]:
     """Serialize OutputMetadata into a dictionary."""
     if not output_metadata_dictionary:
@@ -104,17 +106,16 @@ def _serialize_output_metadata_field(
     dictionary_value = {}
     for output_name, output_metadata in output_metadata_dictionary.items():
         dictionary_value[output_name] = {
-            "graphql_type": str(output_metadata["graphql_type"]),
-            "optional": output_metadata["optional"],
-            "folded": output_metadata["folded"],
-            "provider_metadata": output_metadata["provider_metadata"],
+            "type": str(output_metadata.type),
+            "optional": output_metadata.optional,
+            "folded": output_metadata.folded,
         }
     return dictionary_value
 
 
 def _deserialize_output_metadata_field(
     dict_value: Optional[Dict[str, Dict[str, Any]]]
-) -> Optional[Dict[str, "OutputMetadata"]]:
+) -> Optional[Dict[str, OutputMetadata]]:
     """Deserialize the dictionary representation of OutputMetadata."""
     if not dict_value:
         return None
@@ -122,16 +123,10 @@ def _deserialize_output_metadata_field(
     for output_name, output_metadata in dict_value.items():
         output_metadata_dictionary[output_name] = OutputMetadata(
             type=_type_from_scalar_type_dictionary(
-                ALL_SCALAR_TYPES, parse_type(output_metadata["graphql_type"])
+                ALL_SCALAR_TYPES, parse_type(output_metadata["type"])
             ),
             optional=output_metadata["optional"],
             folded=output_metadata["folded"],
-            provider_metadata=ProviderMetadata(
-                backend_type=output_metadata["provider_metadata"]["backend_type"],
-                requires_fold_postprocessing=output_metadata["provider_metadata"][
-                    "requires_fold_postprocessing"
-                ],
-            ),
         )
     return output_metadata_dictionary
 
@@ -171,8 +166,8 @@ def _deserialize_input_metadata_field(
 
 
 def _compare_input_metadata_field(
-    left_input_metadata: Optional[Dict[str, GraphQLType]],
-    right_input_metadata: Optional[Dict[str, GraphQLType]],
+    left_input_metadata: Optional[Dict[str, QueryArgumentGraphQLType]],
+    right_input_metadata: Optional[Dict[str, QueryArgumentGraphQLType]],
 ) -> bool:
     """Check input_metadata SimpleExecute field equality, comparing GraphQLTypes appropriately."""
     if left_input_metadata is None:
@@ -200,11 +195,29 @@ def _compare_input_metadata_field(
     return True
 
 
+def _deserialize_independent_query_plan_field(dict_value: Dict[str, Any]) -> "IndependentQueryPlan":
+    """Deserialize the dict representation of IndependentQueryPlan."""
+    # Note: there will be more types of IndependentQueryPlans that will require different
+    # deserialization shortly.
+    return SimpleExecute.from_dict(dict_value)
+
+
 # ############
 # Public API #
 # ############
 
 
+@dataclass(init=True, repr=True, eq=True, frozen=True)
+class ProviderMetadata(DataClassJsonMixin):
+    """Metadata about the provider."""
+
+    # Name of the type of provider (ex. PostgreSQL, Cypher, etc).
+    backend_type: str
+
+    # Whether this backend requires MSSQL fold postprocessing for folded outputs.
+    requires_fold_postprocessing: bool
+
+
 @dataclass(init=True, repr=True, eq=True, frozen=True)
 class QueryPlanNode(DataClassJsonMixin, metaclass=ABCMeta):
     """Abstract query plan node. May or may not contain other nodes, depending on its type."""
@@ -220,6 +233,7 @@ class SimpleExecute(QueryPlanNode):
     """Just give the specified query and args to the provider, it'll execute it for you as-is."""
 
     provider_id: str
+    provider_metadata: ProviderMetadata
     query: str  # in whatever query language the provider will accept (not necessarily GraphQL)
     arguments: Dict[str, Any]
 
@@ -229,7 +243,7 @@ class SimpleExecute(QueryPlanNode):
             encoder=_serialize_output_metadata_field, decoder=_deserialize_output_metadata_field
         )
     )
-    input_metadata: Dict[str, GraphQLType] = field(
+    input_metadata: Dict[str, QueryArgumentGraphQLType] = field(
         metadata=config(
             encoder=_serialize_input_metadata_field, decoder=_deserialize_input_metadata_field
         )
@@ -249,3 +263,33 @@ def __eq__(self, other: Any) -> bool:
             and self.output_metadata == other.output_metadata
             and _compare_input_metadata_field(self.input_metadata, other.input_metadata)
         )
+
+
+# More types of IndependentQueryPlans will be added in the future.
+IndependentQueryPlan = SimpleExecute
+
+
+@dataclass(init=True, repr=True, eq=True, frozen=True)
+class QueryPlan(DataClassJsonMixin):
+    """A description of the execution of a GraphQL query, including pagination and joins."""
+
+    # Version number, so we can make breaking changes without requiring lock-step upgrades.
+    # Clients should report supported version ranges when requesting a plan, and the server
+    # should pick the highest version that is supported by both client and server.
+    version: int
+
+    # Metadata on which provider produced the plan, and for what inputs.
+    provider_id: str
+    input_graphql_query: str
+    input_parameters: Dict[str, Any]
+    desired_page_size: Optional[int]
+    output_metadata: Dict[str, OutputMetadata] = field(
+        metadata=config(
+            encoder=_serialize_output_metadata_field, decoder=_deserialize_output_metadata_field
+        )
+    )
+
+    # The actual query plan.
+    plan_root_node: IndependentQueryPlan = field(
+        metadata=config(decoder=_deserialize_independent_query_plan_field)
+    )
diff --git a/graphql_compiler/schema/schema_info.py b/graphql_compiler/schema/schema_info.py
index da44351fa..1a2d8e312 100644
--- a/graphql_compiler/schema/schema_info.py
+++ b/graphql_compiler/schema/schema_info.py
@@ -162,12 +162,13 @@ class SQLSchemaInfo(BackendSpecificSchemaInfo):
     # Specifying the dialect for which we are compiling
     # e.g. sqlalchemy.dialects.mssql.dialect()
     dialect: Dialect
+
     # dict mapping every GraphQL object type or interface type name in the schema to
     # a sqlalchemy table.
     # Column types that do not exist for this dialect are not allowed.
     # All tables are expected to have primary keys.
-
     vertex_name_to_table: Dict[str, sqlalchemy.Table]
+
     # dict mapping every GraphQL object type or interface type name in the schema to
     # dict mapping every vertex field name at that type to a JoinDescriptor.
     # The tables the join is to be performed on are not specified.
@@ -226,56 +227,63 @@ def _create_sql_schema_info(
 )
 
 
-# Complete schema information sufficient to compile GraphQL queries to SQLAlchemy
-#
-# It describes the tables that correspond to each type (object type or interface type),
-# and gives instructions on how to perform joins for each vertex field. The property fields on each
-# type are implicitly mapped to columns with the same name on the corresponding table.
-#
-# NOTES:
-# - RootSchemaQuery is a special type that does not need a corresponding table.
-# - Builtin types like __Schema, __Type, etc. don't need corresponding tables.
-# - Builtin fields like _x_count do not need corresponding columns.
-SQLAlchemySchemaInfo = namedtuple(
-    "SQLAlchemySchemaInfo",
-    (
-        # GraphQLSchema
-        "schema",
-        # optional dict of GraphQL interface or type -> GraphQL union.
-        # Used as a workaround for GraphQL's lack of support for
-        # inheritance across "types" (i.e. non-interfaces), as well as a
-        # workaround for Gremlin's total lack of inheritance-awareness.
-        # The key-value pairs in the dict specify that the "key" type
-        # is equivalent to the "value" type, i.e. that the GraphQL type or
-        # interface in the key is the most-derived common supertype
-        # of every GraphQL type in the "value" GraphQL union.
-        # Recursive expansion of type equivalence hints is not performed,
-        # and only type-level correctness of this argument is enforced.
-        # See README.md for more details on everything this parameter does.
-        # *****
-        # Be very careful with this option, as bad input here will
-        # lead to incorrect output queries being generated.
-        # *****
-        "type_equivalence_hints",
-        # sqlalchemy.engine.interfaces.Dialect, specifying the dialect we are compiling for
-        # (e.g. sqlalchemy.dialects.mssql.dialect()).
-        "dialect",
-        # dict mapping every graphql object type or interface type name in the schema to
-        # a sqlalchemy table. Column types that do not exist for this dialect are not allowed.
-        # All tables are expected to have primary keys.
-        "vertex_name_to_table",
-        # dict mapping every graphql object type or interface type name in the schema to:
-        #    dict mapping every vertex field name at that type to a JoinDescriptor. The
-        #    tables the join is to be performed on are not specified. They are inferred from
-        #    the schema and the tables dictionary.
-        "join_descriptors",
-    ),
-)
+@dataclass
+class SQLAlchemySchemaInfo:
+    """Complete schema information sufficient to compile GraphQL queries to SQLAlchemy.
+
+    It describes the tables that correspond to each type (object type or interface type),
+    and gives instructions on how to perform joins for each vertex field. The property fields on
+    each type are implicitly mapped to columns with the same name on the corresponding table.
+
+    Notes:
+    - RootSchemaQuery is a special type that does not need a corresponding table.
+    - Builtin types like __Schema, __Type, etc. don't need corresponding tables.
+    - Builtin fields like _x_count do not need corresponding columns.
+
+    TODO: This class is essentially the same as SQLSchemaInfo. SQLSchemaInfo is part of an
+          incomplete refactor started in
+          https://github.com/kensho-technologies/graphql-compiler/pull/714
+          SQLAlchemySchemaInfo is currently used to compile GraphQL to SQL while CommonSchemaInfo
+          is currently used to compile GraphQL to match, gremlin, and cypher.
+    """
+
+    schema: GraphQLSchema
+
+    # Optional dict of GraphQL interface or type -> GraphQL union.
+    # Used as a workaround for GraphQL's lack of support for
+    # inheritance across "types" (i.e. non-interfaces), as well as a
+    # workaround for Gremlin's total lack of inheritance-awareness.
+    # The key-value pairs in the dict specify that the "key" type
+    # is equivalent to the "value" type, i.e. that the GraphQL type or
+    # interface in the key is the most-derived common supertype
+    # of every GraphQL type in the "value" GraphQL union.
+    # Recursive expansion of type equivalence hints is not performed,
+    # and only type-level correctness of this argument is enforced.
+    # See README.md for more details on everything this parameter does.
+    # *****
+    # Be very careful with this option, as bad input here will
+    # lead to incorrect output queries being generated.
+    # *****
+    type_equivalence_hints: Optional[TypeEquivalenceHintsType]
+
+    # Specifying the SQL Dialect.
+    dialect: Dialect
+
+    # Mapping every GraphQL object or interface type name in the schema to the corresponding
+    # SQLAlchemy table. Column types that do not exist for this dialect are not allowed.
+    # All tables are expected to have primary keys.
+    vertex_name_to_table: Dict[str, sqlalchemy.Table]
+
+    # Mapping every GraphQL object or interface type name in the schema to:
+    #    dict mapping every vertex field name at that type to a JoinDescriptor. The
+    #    tables the join is to be performed on are not specified. They are inferred from
+    #    the schema and the tables dictionary.
+    join_descriptors: Dict[str, Dict[str, JoinDescriptor]]
 
 
 def make_sqlalchemy_schema_info(
     schema: GraphQLSchema,
-    type_equivalence_hints: TypeEquivalenceHintsType,
+    type_equivalence_hints: Optional[TypeEquivalenceHintsType],
     dialect: Dialect,
     vertex_name_to_table: Dict[str, sqlalchemy.Table],
     join_descriptors: Dict[str, Dict[str, JoinDescriptor]],
diff --git a/graphql_compiler/schema/typedefs.py b/graphql_compiler/schema/typedefs.py
index d00ad7426..10304b190 100644
--- a/graphql_compiler/schema/typedefs.py
+++ b/graphql_compiler/schema/typedefs.py
@@ -19,7 +19,7 @@
 # Dict of GraphQL type name -> (Dict of field name on that type -> the desired type of the field)
 ClassToFieldTypeOverridesType = Dict[str, Dict[str, GraphQLSchemaFieldType]]
 
-# The type of the type equivalence hints object, which defines which GraphQL intefaces and object
+# The type of the type equivalence hints object, which defines which GraphQL interfaces and object
 # types should be considered equivalent to which union types. This is our workaround for the lack
 # of interface-interface and object-object inheritance.
 TypeEquivalenceHintsType = Dict[Union[GraphQLInterfaceType, GraphQLObjectType], GraphQLUnionType]
diff --git a/graphql_compiler/tests/schema_generation_tests/test_sqlalchemy_schema_generation.py b/graphql_compiler/tests/schema_generation_tests/test_sqlalchemy_schema_generation.py
index d6af1cc7a..8883fc4d6 100644
--- a/graphql_compiler/tests/schema_generation_tests/test_sqlalchemy_schema_generation.py
+++ b/graphql_compiler/tests/schema_generation_tests/test_sqlalchemy_schema_generation.py
@@ -112,12 +112,26 @@ def test_table_vertex_representation_with_non_default_name(self) -> None:
 
     def test_represent_supported_fields(self) -> None:
         table1_graphql_object = self.schema_info.schema.get_type("Table1")
+        # mypy complained even with self.assertIsInstance(table1_graphql_object, GraphQLObjectType)
+        # so performing a manual check.
+        if not isinstance(table1_graphql_object, GraphQLObjectType):
+            raise AssertionError(
+                f"table1_graphql_object expected to be GraphQLObjectType, but was of type "
+                f"{type(table1_graphql_object)}"
+            )
         self.assertEqual(
             table1_graphql_object.fields["column_with_supported_type"].type, GraphQLString
         )
 
     def test_ignored_fields_not_supported(self) -> None:
         table1_graphql_object = self.schema_info.schema.get_type("Table1")
+        # mypy complained even with self.assertIsInstance(table1_graphql_object, GraphQLObjectType)
+        # so performing a manual check.
+        if not isinstance(table1_graphql_object, GraphQLObjectType):
+            raise AssertionError(
+                f"table1_graphql_object expected to be GraphQLObjectType, but was of type "
+                f"{type(table1_graphql_object)}"
+            )
         self.assertTrue("column_with_non_supported_type" not in table1_graphql_object.fields)
 
     def test_warn_when_type_is_not_supported(self) -> None:
@@ -140,11 +154,30 @@ def test_do_not_support_sql_tz_aware_datetime_types(self) -> None:
 
     def test_mssql_scalar_type_representation(self) -> None:
         table1_graphql_object = self.schema_info.schema.get_type("Table1")
+        # mypy complained even with self.assertIsInstance(table1_graphql_object, GraphQLObjectType)
+        # so performing a manual check.
+        if not isinstance(table1_graphql_object, GraphQLObjectType):
+            raise AssertionError(
+                f"table1_graphql_object expected to be GraphQLObjectType, but was of type "
+                f"{type(table1_graphql_object)}"
+            )
         self.assertEqual(table1_graphql_object.fields["column_with_mssql_type"].type, GraphQLInt)
 
     def test_direct_sql_edge_representation(self) -> None:
         table1_graphql_object = self.schema_info.schema.get_type("Table1")
         arbitrarily_named_graphql_object = self.schema_info.schema.get_type("ArbitraryObjectName")
+        # mypy complained even with self.assertIsInstance(table1_graphql_object, GraphQLObjectType)
+        # so performing a manual check.
+        if not isinstance(table1_graphql_object, GraphQLObjectType):
+            raise AssertionError(
+                f"table1_graphql_object expected to be GraphQLObjectType, but was of type "
+                f"{type(table1_graphql_object)}"
+            )
+        if not isinstance(arbitrarily_named_graphql_object, GraphQLObjectType):
+            raise AssertionError(
+                f"arbitrarily_named_graphql_object expected to be GraphQLObjectType, but was of "
+                f"type {type(arbitrarily_named_graphql_object)}"
+            )
         self.assertEqual(
             table1_graphql_object.fields["out_test_edge"].type.of_type.name, "ArbitraryObjectName"
         )

From c31d8f1a8f022e6df3dc4ade7a1878cb0af3cfa3 Mon Sep 17 00:00:00 2001
From: Selene Chew <selene.chew@kensho.com>
Date: Fri, 16 Apr 2021 12:49:44 -0400
Subject: [PATCH 3/5] add execute_query_plan

---
 .../make_query_plan.py                        |  4 ++--
 .../sync_query_execution.py                   | 22 ++++++++++++++++++-
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/graphql_compiler/query_planning_and_execution/make_query_plan.py b/graphql_compiler/query_planning_and_execution/make_query_plan.py
index d2e60be9e..11bff1142 100644
--- a/graphql_compiler/query_planning_and_execution/make_query_plan.py
+++ b/graphql_compiler/query_planning_and_execution/make_query_plan.py
@@ -122,7 +122,7 @@ def _make_simple_execute_node(
             compilation_result = compile_graphql_to_match(
                 schema_info, query_and_parameters.query_string
             )
-        # TODO: add InterpreterAdapter based backends
+        # TODO(selene): add InterpreterAdapter based backends
         else:
             raise AssertionError(f"Unknown non-SQL backend_type {backend_type}.")
         # Extract the query and create provider_metadata (process is the same across Cypher,
@@ -379,7 +379,7 @@ def generate_query_plan(
         by the provider_id.
 
     """
-    # TODO: look up schema_info and backend_type by provider_id
+    # TODO(selene): look up schema_info and backend_type by provider_id
     schema_info = None
     backend_type = None
     query_plan_node = _make_simple_execute_node(
diff --git a/graphql_compiler/query_planning_and_execution/sync_query_execution.py b/graphql_compiler/query_planning_and_execution/sync_query_execution.py
index 13de793a7..e8453bf90 100644
--- a/graphql_compiler/query_planning_and_execution/sync_query_execution.py
+++ b/graphql_compiler/query_planning_and_execution/sync_query_execution.py
@@ -3,7 +3,7 @@
 
 from ..post_processing.sql_post_processing import post_process_mssql_folds
 from ..query_formatting.common import deserialize_multiple_arguments
-from .typedefs import QueryExecutionFunc, SimpleExecute
+from .typedefs import QueryExecutionFunc, QueryPlan, SimpleExecute
 
 
 def _execute_simple_execute_node(
@@ -28,3 +28,23 @@ def _execute_simple_execute_node(
 
         # Otherwise, return result as is.
         return result
+
+
+######
+# Public API
+######
+
+
+def execute_query_plan(
+    provider_client_makers: Dict[str, Callable[[], ContextManager[QueryExecutionFunc]]],
+    query_plan: QueryPlan,
+) -> Iterable[Mapping[str, Any]]:
+    """Execute a QueryPlan."""
+    # TODO(selene): figure out if we want some sort of class to contain provider_client_makers
+    if isinstance(query_plan.plan_root_node, SimpleExecute):
+        return _execute_simple_execute_node(provider_client_makers, query_plan.plan_root_node)
+    else:
+        raise NotImplementedError(
+            f"Received plan_root_node with unsupported type "
+            f"{type(query_plan.plan_root_node)}: {query_plan.plan_root_node}"
+        )

From ba8c663c688e11f117dead8bda0f06df07da043c Mon Sep 17 00:00:00 2001
From: Selene Chew <selene.chew@kensho.com>
Date: Mon, 26 Apr 2021 13:36:29 -0400
Subject: [PATCH 4/5] fix spacing

---
 graphql_compiler/query_planning/typedefs.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/graphql_compiler/query_planning/typedefs.py b/graphql_compiler/query_planning/typedefs.py
index 9f2e4e62a..ce10bb6cb 100644
--- a/graphql_compiler/query_planning/typedefs.py
+++ b/graphql_compiler/query_planning/typedefs.py
@@ -209,6 +209,7 @@ def _deserialize_independent_query_plan_field(dict_value: Dict[str, Any]) -> "In
 # Public API #
 # ############
 
+
 @unique
 class BackendType(Enum):
     # N.B.: The values of the enums are the "human-friendly" display names. Since they are shown

From 646db34d4205d3cfb27c08653694372dc55a0854 Mon Sep 17 00:00:00 2001
From: Selene Chew <selene.chew@kensho.com>
Date: Mon, 26 Apr 2021 18:09:00 -0400
Subject: [PATCH 5/5] use enums for backend type

---
 .../query_planning/make_query_plan.py         | 34 ++++++++++++-------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/graphql_compiler/query_planning/make_query_plan.py b/graphql_compiler/query_planning/make_query_plan.py
index 11bff1142..fea2be85f 100644
--- a/graphql_compiler/query_planning/make_query_plan.py
+++ b/graphql_compiler/query_planning/make_query_plan.py
@@ -18,13 +18,9 @@
     StringValueNode,
 )
 from graphql.pyutils import FrozenList
-from sqlalchemy.dialects.mssql.base import MSDialect
 
 from ..ast_manipulation import get_only_query_definition
 from ..compiler.common import (
-    CYPHER_LANGUAGE,
-    GREMLIN_LANGUAGE,
-    MATCH_LANGUAGE,
     compile_graphql_to_cypher,
     compile_graphql_to_gremlin,
     compile_graphql_to_match,
@@ -36,7 +32,7 @@
 from ..schema import FilterDirective, OutputDirective
 from ..schema.schema_info import CommonSchemaInfo, SQLAlchemySchemaInfo
 from ..schema_transformation.split_query import AstType, SubQueryNode
-from .typedefs import ProviderMetadata, QueryPlan, SimpleExecute
+from .typedefs import BackendType, ProviderMetadata, QueryPlan, SimpleExecute
 
 
 @dataclass
@@ -85,7 +81,7 @@ def _make_simple_execute_node(
     query_and_parameters: QueryStringWithParameters,
     schema_info: Union[CommonSchemaInfo, SQLAlchemySchemaInfo],
     provider_id: str,
-    backend_type: Optional[str],
+    backend_type: BackendType,
 ) -> SimpleExecute:
     """Generate a SimpleExecuteNode.
 
@@ -93,32 +89,44 @@ def _make_simple_execute_node(
         query_and_parameters: the query and parameters for which to create a SimpleExecute.
         schema_info: schema information to use for query compilation.
         provider_id: the identifier of the provider to be queried.
-        backend_type: the backend type. Note: this is inferred from the SQLAlchemySchemaInfo's
-                      dialect for SQL backends.
+        backend_type: the backend type. Note: if schema_info is of type SQLAlchemySchemaInfo, the
+                      backend_type must be a flavor of SQL.
 
     Returns:
         SimpleExecute with all necessary information to execute the given query_and_parameters.
 
     """
+    # Ensure that if a SQL schema info object is passed, that the backend type is a SQL dialect.
     if isinstance(schema_info, SQLAlchemySchemaInfo):
         # Compiled SQL query.
         compilation_result = compile_graphql_to_sql(schema_info, query_and_parameters.query_string)
         query = print_sqlalchemy_query_string(compilation_result.query, schema_info.dialect)
 
+        # Determine if the SQL dialect requires post-processing.
+        if backend_type == BackendType.mssql:
+            requires_fold_postprocessing = True
+        elif backend_type == BackendType.postgresql:
+            requires_fold_postprocessing = False
+        else:
+            raise AssertionError(
+                f"Received SQLAlchemySchemaInfo, but a non-SQL backend type {backend_type}."
+            )
+
         provider_metadata = ProviderMetadata(
-            backend_type=schema_info.dialect.name,
-            requires_fold_postprocessing=isinstance(schema_info.dialect, MSDialect),
+            backend_type=backend_type,
+            requires_fold_postprocessing=requires_fold_postprocessing,
         )
+    # All other backends use CommonSchemaInfo.
     else:
-        if backend_type == CYPHER_LANGUAGE:
+        if backend_type == BackendType.cypher:
             compilation_result = compile_graphql_to_cypher(
                 schema_info, query_and_parameters.query_string
             )
-        elif backend_type == GREMLIN_LANGUAGE:
+        elif backend_type == BackendType.gremlin:
             compilation_result = compile_graphql_to_gremlin(
                 schema_info, query_and_parameters.query_string
             )
-        elif backend_type == MATCH_LANGUAGE:
+        elif backend_type == BackendType.match:
             compilation_result = compile_graphql_to_match(
                 schema_info, query_and_parameters.query_string
             )