Allow querying an EmbeddedModelField by model instance

django_mongodb_backend/fields/embedded_model.py

@@ -3,10 +3,13 @@
 from django.core import checks
 from django.core.exceptions import FieldDoesNotExist
 from django.db import models
+from django.db.models import lookups
+from django.db.models.expressions import Col
 from django.db.models.fields.related import lazy_related_operation
 from django.db.models.lookups import Transform
 
 from .. import forms
+from ..query_utils import process_lhs, process_rhs
 from .json import build_json_mql_path
 
 
@@ -149,6 +152,66 @@ def formfield(self, **kwargs):
         )
 
 
+@EmbeddedModelField.register_lookup
+class EMFExact(lookups.Exact):
+    def model_to_dict(self, instance):
+        """
+        Return a dict containing the data in a model instance, as well as a
+        dict containing the data for any embedded model fields.
+        """
+        data = {}
+        emf_data = {}
+        for f in instance._meta.concrete_fields:
+            value = f.value_from_object(instance)
+            if isinstance(f, EmbeddedModelField):
+                emf_data[f.name] = self.model_to_dict(value) if value is not None else (None, {})
+                continue
+            # Unless explicitly set, primary keys aren't included in embedded
+            # models.
+            if f.primary_key and value is None:
+                continue
+            data[f.name] = value
+        return data, emf_data
+
+    def get_conditions(self, emf_data, prefix=None):
+        """
+        Recursively transform a dictionary of {"field_name": {<model_to_dict>}}
+        lookups into MQL. `prefix` tracks the string that must be appended to
+        nested fields.
+        """
+        conditions = []
+        for k, v in emf_data.items():
+            v, emf_data = v
+            subprefix = f"{prefix}.{k}" if prefix else k
+            conditions += self.get_conditions(emf_data, subprefix)
+            if v is not None:
+                # Match all field of the EmbeddedModelField.
+                conditions += [{"$eq": [f"{subprefix}.{x}", y]} for x, y in v.items()]
+            else:
+                # Match a null EmbeddedModelField.
+                conditions += [{"$eq": [f"{subprefix}", None]}]
+        return conditions
+
+    def as_mql(self, compiler, connection):
+        lhs_mql = process_lhs(self, compiler, connection)
+        value = process_rhs(self, compiler, connection)
+        if isinstance(self.lhs, Col) or (
+            isinstance(self.lhs, KeyTransform)
+            and isinstance(self.lhs.ref_field, EmbeddedModelField)
+        ):
+            if isinstance(value, models.Model):
+                value, emf_data = self.model_to_dict(value)
+                prefix = self.lhs.as_mql(compiler, connection)
+                # Get conditions for any nested EmbeddedModelFields.
+                conditions = self.get_conditions({prefix: (value, emf_data)})
+                return {"$and": conditions}
+            raise TypeError(
+                "An EmbeddedModelField must be queried using a model instance, got %s."
+                % type(value)
+            )
+        return connection.mongo_operators[self.lookup_name](lhs_mql, value)
+
+
 class KeyTransform(Transform):
     def __init__(self, key_name, ref_field, *args, **kwargs):
         super().__init__(*args, **kwargs)
@@ -192,8 +255,14 @@ def preprocess_lhs(self, compiler, connection):
                 json_key_transforms.insert(0, previous.key_name)
             previous = previous.lhs
         mql = previous.as_mql(compiler, connection)
-        # The first json_key_transform is the field name.
-        embedded_key_transforms.append(json_key_transforms.pop(0))
+        try:
+            # The first json_key_transform is the field name.
+            field_name = json_key_transforms.pop(0)
+        except IndexError:
+            # This is a lookup of the embedded model itself.
+            pass
+        else:
+            embedded_key_transforms.append(field_name)
         return mql, embedded_key_transforms, json_key_transforms
 
     def as_mql(self, compiler, connection):

docs/source/releases/5.1.x.rst

@@ -2,6 +2,14 @@
 Django MongoDB Backend 5.1.x
 ============================
 
+5.1.0 beta 2
+============
+
+*Unreleased*
+
+- Added support to ``EmbeddedModelField`` for the ``QuerySet`` ``exact`` lookup
+  using a model instance.
+
 5.1.0 beta 1
 ============
 

docs/source/topics/embedded-models.rst

@@ -54,3 +54,12 @@ as relational fields. For example, to retrieve all customers who have an
 address with the city "New York"::
 
     >>> Customer.objects.filter(address__city="New York")
+
+You can also query using a model instance. Unlike a normal relational lookup
+which does the lookup by primary key, since embedded models typically don't
+have a primary key set, the query requires that every field match. For example,
+this query gives customers with addresses with the city "New York" and all
+other fields of the address equal to their default (:attr:`Field.default
+<django.db.models.Field.default>`, ``None``, or an empty string).
+
+    >>> Customer.objects.filter(address=Address(city="New York"))

tests/model_fields_/models.py

@@ -130,3 +130,31 @@ class Library(models.Model):
 
     def __str__(self):
         return self.name
+
+
+class A(models.Model):
+    b = EmbeddedModelField("B")
+
+
+class B(EmbeddedModel):
+    c = EmbeddedModelField("C")
+    name = models.CharField(max_length=100)
+    value = models.IntegerField()
+
+
+class C(EmbeddedModel):
+    d = EmbeddedModelField("D")
+    name = models.CharField(max_length=100)
+    value = models.IntegerField()
+
+
+class D(EmbeddedModel):
+    e = EmbeddedModelField("E")
+    nullable_e = EmbeddedModelField("E", null=True, blank=True)
+    name = models.CharField(max_length=100)
+    value = models.IntegerField()
+
+
+class E(EmbeddedModel):
+    name = models.CharField(max_length=100)
+    value = models.IntegerField()

tests/model_fields_/test_embedded_model.py

@@ -2,7 +2,7 @@
 from datetime import timedelta
 
 from django.core.exceptions import FieldDoesNotExist, ValidationError
-from django.db import models
+from django.db import connection, models
 from django.db.models import (
     Exists,
     ExpressionWrapper,
@@ -17,14 +17,7 @@
 from django_mongodb_backend.fields import EmbeddedModelField
 from django_mongodb_backend.models import EmbeddedModel
 
-from .models import (
-    Address,
-    Author,
-    Book,
-    Data,
-    Holder,
-    Library,
-)
+from .models import A, Address, Author, B, Book, C, D, Data, E, Holder, Library
 from .utils import truncate_ms
 
 
@@ -117,6 +110,66 @@ def test_order_by_embedded_field(self):
         qs = Holder.objects.filter(data__integer__gt=3).order_by("-data__integer")
         self.assertSequenceEqual(qs, list(reversed(self.objs[4:])))
 
+    def test_exact_with_model(self):
+        data = Holder.objects.first().data
+        self.assertEqual(
+            Holder.objects.filter(data=data).get().data.integer, self.objs[0].data.integer
+        )
+
+    def test_exact_with_model_ignores_key_order(self):
+        # Due to the possibility of schema changes or the reordering of a
+        # model's fields, a lookup must work if an embedded document has its
+        # keys in a different order than what's declared on the embedded model.
+        connection.get_collection("model_fields__holder").insert_one(
+            {
+                "data": {
+                    "auto_now": None,
+                    "auto_now_add": None,
+                    "json_value": None,
+                    "integer": 100,
+                }
+            }
+        )
+        self.assertEqual(Holder.objects.filter(data=Data(integer=100)).get().data.integer, 100)
+
+    def test_exact_with_nested_model(self):
+        address = Address(city="NYC", state="NY")
+        author = Author(name="Shakespeare", age=55, address=address)
+        obj = Book.objects.create(author=author)
+        self.assertCountEqual(Book.objects.filter(author=author), [obj])
+        self.assertCountEqual(Book.objects.filter(author__address=address), [obj])
+
+    def test_exact_with_deeply_nested_models(self):
+        e1 = E(name="E1", value=5)
+        d1 = D(name="D1", value=4, e=e1)
+        c1 = C(name="C1", value=3, d=d1)
+        b1 = B(name="B1", value=2, c=c1)
+        a1 = A.objects.create(b=b1)
+        e2 = E(name="E2", value=6)
+        d2 = D(name="D2", value=4, e=e1, nullable_e=e2)
+        c2 = C(name="C2", value=3, d=d2)
+        b2 = B(name="B2", value=2, c=c2)
+        a2 = A.objects.create(b=b2)
+        self.assertCountEqual(A.objects.filter(b=b1), [a1])
+        self.assertCountEqual(A.objects.filter(b__c=c1), [a1])
+        self.assertCountEqual(A.objects.filter(b__c__d=d1), [a1])
+        self.assertCountEqual(A.objects.filter(b__c__d__e=e1), [a1, a2])
+        self.assertCountEqual(A.objects.filter(b=b2), [a2])
+        self.assertCountEqual(A.objects.filter(b__c=c2), [a2])
+        self.assertCountEqual(A.objects.filter(b__c__d=d2), [a2])
+        self.assertCountEqual(A.objects.filter(b__c__d__nullable_e=e2), [a2])
+
+    def test_exact_validates_argument(self):
+        msg = "An EmbeddedModelField must be queried using a model instance, got <class 'dict'>."
+        with self.assertRaisesMessage(TypeError, msg):
+            str(A.objects.filter(b={}))
+        with self.assertRaisesMessage(TypeError, msg):
+            str(A.objects.filter(b__c={}))
+        with self.assertRaisesMessage(TypeError, msg):
+            str(A.objects.filter(b__c__d={}))
+        with self.assertRaisesMessage(TypeError, msg):
+            str(A.objects.filter(b__c__d__e={}))
+
     def test_embedded_json_field_lookups(self):
         objs = [
             Holder.objects.create(