don't connect to MongoDB immediately (fixes #87)

Author: dcrosta

docs/index.rst

@@ -91,12 +91,13 @@ constructor. These are passed directly through to the underlying
 
 .. note::
 
-    Unless you specify otherwise, PyMongo will attempt to connect to your
-    MongoDB server immediately (within the call to :meth:`init_app` in the
-    case of Flask-PyMongo). If the web server you are running Flask in loads
-    your application before forking, you may experience problems. In these
-    cases, you are advised to pass ``connect=False`` to ``PyMongo``, or
-    append ``?connect=false`` to your MongoDB URI.
+    By default, Flask-PyMongo sets the ``connect`` keyword argument to
+    ``False``, to prevent PyMongo from connecting immediately. PyMongo
+    itself `is not fork-safe
+    <http://api.mongodb.com/python/current/faq.html#is-pymongo-fork-safe>`_,
+    and delaying connection until the app is actually used is necessary to
+    avoid issues. If you wish to change this default behavior, pass
+    ``connect=True`` as a keyword argument to ``PyMongo``.
 
 You can create multiple ``PyMongo`` instances, to connect to multiple
 databases or database servers:
@@ -173,6 +174,7 @@ Changes:
   `issue #110 <https://github.com/dcrosta/flask-pymongo/issues/110>`_.
 
   - Only support configuration via URI.
+  - Don't connect to MongoDB by default.
   - Clarify version support of Python, Flask, PyMongo, and MongoDB.
   - Readability improvement to ``README.md`` (MinJae Kwon).
 

flask_pymongo/__init__.py

@@ -149,6 +149,10 @@ def init_app(self, app, uri=None, *args, **kwargs):
         parsed_uri = uri_parser.parse_uri(uri)
         database_name = parsed_uri["database"]
 
+        # Try to delay connecting, in case the app is loaded before forking, per
+        # http://api.mongodb.com/python/current/faq.html#is-pymongo-fork-safe
+        kwargs.setdefault("connect", False)
+
         self.cx = MongoClient(*args, **kwargs)
         self.db = self.cx[database_name]
 

flask_pymongo/tests/test_config.py

@@ -1,11 +1,16 @@
 import time
 
 import pymongo
+import pytest
 
 from flask_pymongo.tests.util import FlaskRequestTest
 import flask_pymongo
 
 
+class CouldNotConnect(Exception):
+    pass
+
+
 class FlaskPyMongoConfigTest(FlaskRequestTest):
 
     def setUp(self):
@@ -32,7 +37,7 @@ def test_config_with_uri_in_flask_conf_var(self):
         uri = "mongodb://localhost:{}/{}".format(self.port, self.dbname)
         self.app.config["MONGO_URI"] = uri
 
-        mongo = flask_pymongo.PyMongo(self.app)
+        mongo = flask_pymongo.PyMongo(self.app, connect=True)
 
         _wait_until_connected(mongo)
         assert mongo.db.name == self.dbname
@@ -41,7 +46,7 @@ def test_config_with_uri_in_flask_conf_var(self):
     def test_config_with_uri_passed_directly(self):
         uri = "mongodb://localhost:{}/{}".format(self.port, self.dbname)
 
-        mongo = flask_pymongo.PyMongo(self.app, uri)
+        mongo = flask_pymongo.PyMongo(self.app, uri, connect=True)
 
         _wait_until_connected(mongo)
         assert mongo.db.name == self.dbname
@@ -68,11 +73,19 @@ class CustomDict(dict):
 
         assert type(mongo.db.things.find_one()) == CustomDict
 
+    def test_it_doesnt_connect_by_default(self):
+        uri = "mongodb://localhost:{}/{}".format(self.port, self.dbname)
+
+        mongo = flask_pymongo.PyMongo(self.app, uri)
+
+        with pytest.raises(CouldNotConnect):
+            _wait_until_connected(mongo, timeout=0.2)
+
 
 def _wait_until_connected(mongo, timeout=1.0):
     start = time.time()
     while time.time() < (start + timeout):
         if mongo.cx.nodes:
             return
         time.sleep(0.05)
-    raise RuntimeError("could not prove mongodb connected in %r seconds" % timeout)
+    raise CouldNotConnect("could not prove mongodb connected in %r seconds" % timeout)