Arrayfield+emf subquerying

django_mongodb_backend/fields/array.py

@@ -338,7 +338,7 @@ class ArrayLenTransform(Transform):
 
     def as_mql(self, compiler, connection):
         lhs_mql = process_lhs(self, compiler, connection)
-        return {"$cond": {"if": {"$eq": [lhs_mql, None]}, "then": None, "else": {"$size": lhs_mql}}}
+        return {"$cond": {"if": {"$isArray": lhs_mql}, "then": {"$size": lhs_mql}, "else": None}}
 
 
 @ArrayField.register_lookup

django_mongodb_backend/fields/embedded_model.py

@@ -186,8 +186,9 @@ def as_mql(self, compiler, connection):
             key_transforms.insert(0, previous.key_name)
             previous = previous.lhs
         mql = previous.as_mql(compiler, connection)
-        transforms = ".".join(key_transforms)
-        return f"{mql}.{transforms}"
+        for key in key_transforms:
+            mql = {"$getField": {"input": mql, "field": key}}
+        return mql
 
     @property
     def output_field(self):

django_mongodb_backend/fields/embedded_model_array.py

@@ -1,8 +1,14 @@
-from django.db.models import Field
+import difflib
+
+from django.core.exceptions import FieldDoesNotExist
+from django.db.models import Field, lookups
+from django.db.models.expressions import Col
+from django.db.models.lookups import Lookup, Transform
 
 from .. import forms
+from ..query_utils import process_lhs, process_rhs
 from . import EmbeddedModelField
-from .array import ArrayField
+from .array import ArrayField, ArrayLenTransform
 
 
 class EmbeddedModelArrayField(ArrayField):
@@ -44,3 +50,233 @@ def formfield(self, **kwargs):
                 **kwargs,
             },
         )
+
+    def get_transform(self, name):
+        transform = super().get_transform(name)
+        if transform:
+            return transform
+        return KeyTransformFactory(name, self)
+
+    def _get_lookup(self, lookup_name):
+        lookup = super()._get_lookup(lookup_name)
+        if lookup is None or lookup is ArrayLenTransform:
+            return lookup
+
+        class EmbeddedModelArrayFieldLookups(Lookup):
+            def as_mql(self, compiler, connection):
+                raise ValueError(
+                    "Cannot apply this lookup directly to EmbeddedModelArrayField. "
+                    "Try querying one of its embedded fields instead."
+                )
+
+        return EmbeddedModelArrayFieldLookups
+
+
+class _EmbeddedModelArrayOutputField(ArrayField):
+    """
+    Represents the output of an EmbeddedModelArrayField when traversed in a query path.
+
+    This field is not meant to be used directly in model definitions. It exists solely to
+    support query output resolution; when an EmbeddedModelArrayField is accessed in a query,
+    the result should behave like an array of the embedded model's target type.
+
+    While it mimics ArrayField's lookups behavior, the way those lookups are resolved
+    follows the semantics of EmbeddedModelArrayField rather than native array behavior.
+    """
+
+    ALLOWED_LOOKUPS = {
+        "in",
+        "exact",
+        "iexact",
+        "gt",
+        "gte",
+        "lt",
+        "lte",
+    }
+
+    def get_lookup(self, name):
+        return super().get_lookup(name) if name in self.ALLOWED_LOOKUPS else None
+
+
+class EmbeddedModelArrayFieldBuiltinLookup(Lookup):
+    def process_rhs(self, compiler, connection):
+        value = self.rhs
+        if not self.get_db_prep_lookup_value_is_iterable:
+            value = [value]
+        # Value must be serialized based on the query target.
+        # If querying a subfield inside the array (i.e., a nested KeyTransform), use the output
+        # field of the subfield. Otherwise, use the base field of the array itself.
+        get_db_prep_value = self.lhs._lhs.output_field.get_db_prep_value
+        return None, [
+            v if hasattr(v, "as_mql") else get_db_prep_value(v, connection, prepared=True)
+            for v in value
+        ]
+
+    def as_mql(self, compiler, connection):
+        # Querying a subfield within the array elements (via nested KeyTransform).
+        # Replicates MongoDB's implicit ANY-match by mapping over the array and applying
+        # `$in` on the subfield.
+        lhs_mql = process_lhs(self, compiler, connection)
+        inner_lhs_mql = lhs_mql["$ifNull"][0]["$map"]["in"]
+        values = process_rhs(self, compiler, connection)
+        lhs_mql["$ifNull"][0]["$map"]["in"] = connection.mongo_operators[self.lookup_name](
+            inner_lhs_mql, values
+        )
+        return {"$anyElementTrue": lhs_mql}
+
+
+class ArrayAggregationSubqueryMixin:
+    def get_subquery_wrapping_pipeline(self, compiler, connection, field_name, expr):
+        return [
+            {
+                "$facet": {
+                    "group": [
+                        {"$project": {"tmp_name": expr.as_mql(compiler, connection)}},
+                        {
+                            "$unwind": "$tmp_name",
+                        },
+                        {
+                            "$group": {
+                                "_id": None,
+                                "tmp_name": {"$addToSet": "$tmp_name"},
+                            }
+                        },
+                    ]
+                }
+            },
+            {
+                "$project": {
+                    field_name: {
+                        "$ifNull": [
+                            {
+                                "$getField": {
+                                    "input": {"$arrayElemAt": ["$group", 0]},
+                                    "field": "tmp_name",
+                                }
+                            },
+                            [],
+                        ]
+                    }
+                }
+            },
+        ]
+
+
+@_EmbeddedModelArrayOutputField.register_lookup
+class EmbeddedModelArrayFieldIn(
+    EmbeddedModelArrayFieldBuiltinLookup, lookups.In, ArrayAggregationSubqueryMixin
+):
+    pass
+
+
+@_EmbeddedModelArrayOutputField.register_lookup
+class EmbeddedModelArrayFieldExact(EmbeddedModelArrayFieldBuiltinLookup, lookups.Exact):
+    pass
+
+
+@_EmbeddedModelArrayOutputField.register_lookup
+class EmbeddedModelArrayFieldIExact(EmbeddedModelArrayFieldBuiltinLookup, lookups.IExact):
+    get_db_prep_lookup_value_is_iterable = False
+
+
+@_EmbeddedModelArrayOutputField.register_lookup
+class EmbeddedModelArrayFieldGreaterThan(EmbeddedModelArrayFieldBuiltinLookup, lookups.GreaterThan):
+    pass
+
+
+@_EmbeddedModelArrayOutputField.register_lookup
+class EmbeddedModelArrayFieldGreaterThanOrEqual(
+    EmbeddedModelArrayFieldBuiltinLookup, lookups.GreaterThanOrEqual
+):
+    pass
+
+
+@_EmbeddedModelArrayOutputField.register_lookup
+class EmbeddedModelArrayFieldLessThan(EmbeddedModelArrayFieldBuiltinLookup, lookups.LessThan):
+    pass
+
+
+@_EmbeddedModelArrayOutputField.register_lookup
+class EmbeddedModelArrayFieldLessThanOrEqual(
+    EmbeddedModelArrayFieldBuiltinLookup, lookups.LessThanOrEqual
+):
+    pass
+
+
+class KeyTransform(Transform):
+    def __init__(self, key_name, array_field, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.array_field = array_field
+        self.key_name = key_name
+        # The iteration items begins from the base_field, a virtual column with
+        # base field output type is created.
+        column_target = array_field.embedded_model._meta.get_field(key_name).clone()
+        column_name = f"$item.{key_name}"
+        column_target.db_column = column_name
+        column_target.set_attributes_from_name(column_name)
+        self._lhs = Col(None, column_target)
+        self._sub_transform = None
+
+    def __call__(self, this, *args, **kwargs):
+        self._lhs = self._sub_transform(self._lhs, *args, **kwargs)
+        return self
+
+    def get_lookup(self, name):
+        return self.output_field.get_lookup(name)
+
+    def get_transform(self, name):
+        """
+        Validate that `name` is either a field of an embedded model or a
+        lookup on an embedded model's field.
+        """
+        # Once the sub lhs is a transform, all the filter are applied over it.
+        # Otherwise get transform from EMF.
+        if transform := self._lhs.get_transform(name):
+            if isinstance(transform, KeyTransformFactory):
+                raise ValueError("Cannot perform multiple levels of array traversal in a query.")
+            self._sub_transform = transform
+            return self
+        output_field = self._lhs.output_field
+        allowed_lookups = self.output_field.ALLOWED_LOOKUPS.intersection(
+            set(output_field.get_lookups())
+        )
+        suggested_lookups = difflib.get_close_matches(name, allowed_lookups)
+        if suggested_lookups:
+            suggested_lookups = " or ".join(suggested_lookups)
+            suggestion = f", perhaps you meant {suggested_lookups}?"
+        else:
+            suggestion = ""
+        raise FieldDoesNotExist(
+            f"Unsupported lookup '{name}' for "
+            f"EmbeddedModelArrayField of '{output_field.__class__.__name__}'"
+            f"{suggestion}"
+        )
+
+    def as_mql(self, compiler, connection):
+        inner_lhs_mql = self._lhs.as_mql(compiler, connection)
+        lhs_mql = process_lhs(self, compiler, connection)
+        return {
+            "$ifNull": [
+                {
+                    "$map": {
+                        "input": lhs_mql,
+                        "as": "item",
+                        "in": inner_lhs_mql,
+                    }
+                },
+                [],
+            ]
+        }
+
+    @property
+    def output_field(self):
+        return _EmbeddedModelArrayOutputField(self._lhs.output_field)
+
+
+class KeyTransformFactory:
+    def __init__(self, key_name, base_field):
+        self.key_name = key_name
+        self.base_field = base_field
+
+    def __call__(self, *args, **kwargs):
+        return KeyTransform(self.key_name, self.base_field, *args, **kwargs)