prevent the creation of embedded models

Author: timgraham

django_mongodb_backend/fields/embedded_model.py

@@ -18,7 +18,18 @@ def __init__(self, embedded_model, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
     def check(self, **kwargs):
+        from ..models import EmbeddedModel
+
         errors = super().check(**kwargs)
+        if not issubclass(self.embedded_model, EmbeddedModel):
+            return [
+                checks.Error(
+                    "Embedded model must be a subclass of "
+                    "django_mongodb_backend.models.EmbeddedModel.",
+                    obj=self,
+                    id="django_mongodb.embedded_model.E002",
+                )
+            ]
         for field in self.embedded_model._meta.fields:
             if field.remote_field:
                 errors.append(

django_mongodb_backend/managers.py

@@ -1,7 +1,43 @@
+from django.db import NotSupportedError
 from django.db.models.manager import BaseManager
 
 from .queryset import MongoQuerySet
 
 
 class MongoManager(BaseManager.from_queryset(MongoQuerySet)):
     pass
+
+
+class NoWriteManager(BaseManager):
+    def get_queryset(self):
+        raise NotSupportedError("An EmbeddedModel cannot be queried.")
+
+    def all(self):
+        raise NotSupportedError("An EmbeddedModel cannot be queried.")
+
+    def get(self, *args, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be queried.")
+
+    def get_or_create(self, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be queried.")
+
+    def filter(self, *args, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be queried.")
+
+    def create(self, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be created.")
+
+    def bulk_create(self, *args, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be created.")
+
+    def update(self, *args, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be updated.")
+
+    def bulk_update(self, *args, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be updated.")
+
+    def update_or_create(self, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be updated or created.")
+
+    def delete(self):
+        raise NotSupportedError("An EmbeddedModel cannot be deleted.")

django_mongodb_backend/models.py

@@ -0,0 +1,16 @@
+from django.db import NotSupportedError, models
+
+from .managers import NoWriteManager
+
+
+class EmbeddedModel(models.Model):
+    objects = NoWriteManager()
+
+    class Meta:
+        abstract = True
+
+    def delete(self, *args, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be deleted.")
+
+    def save(self, *args, **kwargs):
+        raise NotSupportedError("An EmbeddedModel cannot be saved.")

django_mongodb_backend/schema.py

@@ -23,6 +23,10 @@ def get_database(self):
 
     @wrap_database_errors
     def create_model(self, model):
+        from .models import EmbeddedModel
+
+        if issubclass(model, EmbeddedModel):
+            return
         self.get_database().create_collection(model._meta.db_table)
         self._create_model_indexes(model)
         # Make implicit M2M tables.
@@ -76,6 +80,10 @@ def _create_model_indexes(self, model, column_prefix="", parent_model=None):
             self.add_index(model, index, column_prefix=column_prefix, parent_model=parent_model)
 
     def delete_model(self, model):
+        from .models import EmbeddedModel
+
+        if issubclass(model, EmbeddedModel):
+            return
         # Delete implicit M2m tables.
         for field in model._meta.local_many_to_many:
             if field.remote_field.through._meta.auto_created:

docs/source/embedded-models.rst

@@ -11,13 +11,14 @@ The basics
 Let's consider this example::
 
    from django_mongodb_backend.fields import EmbeddedModelField
+   from django_mongodb_backend.models import EmbeddedModel
 
    class Customer(models.Model):
        name = models.CharField(...)
        address = EmbeddedModelField("Address")
        ...
 
-   class Address(models.Model):
+   class Address(EmbeddedModel):
        ...
        city = models.CharField(...)
 

docs/source/fields.rst

@@ -224,6 +224,8 @@ Stores a model of type ``embedded_model``.
 
         Specifies the model class to embed. It can be either a concrete model
         class or a :ref:`lazy reference <lazy-relationships>` to a model class.
+        The target model must be a subclass of
+        ``django_mongodb_backend.models.EmbeddedModel``.
 
         The embedded model cannot have relational fields
         (:class:`~django.db.models.ForeignKey`,
@@ -234,11 +236,12 @@ Stores a model of type ``embedded_model``.
 
             from django.db import models
             from django_mongodb_backend.fields import EmbeddedModelField
+            from django_mongodb_backend.models import EmbeddedModel
 
-            class Address(models.Model):
+            class Address(EmbeddedModel):
                 ...
 
-            class Author(models.Model):
+            class Author(EmbeddedModel):
                 address = EmbeddedModelField(Address)
 
             class Book(models.Model):

docs/source/models.rst

@@ -3,6 +3,7 @@
 from django.db import models
 
 from django_mongodb_backend.fields import ArrayField, EmbeddedModelField, ObjectIdField
+from django_mongodb_backend.models import EmbeddedModel
 
 
 # ObjectIdField
@@ -98,19 +99,19 @@ class Holder(models.Model):
     data = EmbeddedModelField("Data", null=True, blank=True)
 
 
-class Data(models.Model):
+class Data(EmbeddedModel):
     integer = models.IntegerField(db_column="custom_column")
     auto_now = models.DateTimeField(auto_now=True)
     auto_now_add = models.DateTimeField(auto_now_add=True)
 
 
-class Address(models.Model):
+class Address(EmbeddedModel):
     city = models.CharField(max_length=20)
     state = models.CharField(max_length=2)
     zip_code = models.IntegerField(db_index=True)
 
 
-class Author(models.Model):
+class Author(EmbeddedModel):
     name = models.CharField(max_length=10)
     age = models.IntegerField()
     address = EmbeddedModelField(Address)

tests/model_fields_/models.py

@@ -4,6 +4,7 @@
 from django.test.utils import isolate_apps
 
 from django_mongodb_backend.fields import EmbeddedModelField
+from django_mongodb_backend.models import EmbeddedModel
 
 from .models import (
     Address,
@@ -108,7 +109,7 @@ def test_nested(self):
 @isolate_apps("model_fields_")
 class CheckTests(SimpleTestCase):
     def test_no_relational_fields(self):
-        class Target(models.Model):
+        class Target(EmbeddedModel):
             key = models.ForeignKey("MyModel", models.CASCADE)
 
         class MyModel(models.Model):
@@ -123,3 +124,20 @@ class MyModel(models.Model):
         self.assertEqual(
             msg, "Embedded models cannot have relational fields (Target.key is a ForeignKey)."
         )
+
+    def test_embedded_model_subclass(self):
+        class Target(models.Model):
+            pass
+
+        class MyModel(models.Model):
+            field = EmbeddedModelField(Target)
+
+        model = MyModel()
+        errors = model.check()
+        self.assertEqual(len(errors), 1)
+        # The inner CharField has a non-positive max_length.
+        self.assertEqual(errors[0].id, "django_mongodb.embedded_model.E002")
+        msg = errors[0].msg
+        self.assertEqual(
+            msg, "Embedded model must be a subclass of django_mongodb_backend.models.EmbeddedModel."
+        )