Add a database router so dumpdata can ignore embedded models

Author: timgraham

django_mongodb_backend/routers.py

@@ -0,0 +1,18 @@
+from django.apps import apps
+
+from django_mongodb_backend.models import EmbeddedModel
+
+
+class MongoRouter:
+    def allow_migrate(self, db, app_label, model_name=None, **hints):
+        """
+        EmbeddedModels don't have their own collection and must be ignored by
+        dumpdata.
+        """
+        if not model_name:
+            return None
+        try:
+            model = apps.get_model(app_label, model_name)
+        except LookupError:
+            return None
+        return False if issubclass(model, EmbeddedModel) else None

docs/source/faq.rst

@@ -32,3 +32,10 @@ logging::
             },
         },
     }
+
+``dumpdata`` fails with ``CommandError: Unable to serialize database``
+----------------------------------------------------------------------
+
+If running ``manage.py dumpdata`` results in ``CommandError: Unable to
+serialize database: 'EmbeddedModelManager' object has no attribute using'``,
+see :ref:`configuring-database-routers-setting`.

docs/source/intro/configure.rst

@@ -154,6 +154,21 @@ it into the format above, you can use
 
 This constructs a :setting:`DATABASES` setting equivalent to the first example.
 
+.. _configuring-database-routers-setting:
+
+Configuring the ``DATABASE_ROUTERS`` setting
+============================================
+
+If you intend to use :doc:`embedded models </topics/embedded-models>`, you must
+configure the :setting:`DATABASE_ROUTERS` setting so that a collection for
+these models isn't created and so that embedded models won't be treated as
+normal models by :djadmin:`dumpdata`::
+
+    DATABASE_ROUTERS = ["django_mongodb_backend.routers.MongoRouter"]
+
+(If you've used the :djadmin:`startproject` template, this line is already
+present.)
+
 Congratulations, your project is ready to go!
 
 .. seealso::

docs/source/releases/5.0.x.rst

@@ -17,6 +17,9 @@ Django MongoDB Backend 5.0.x
 - Added :doc:`async <django:topics/async>` support.
 - Added the ``db_name`` parameter to
   :func:`~django_mongodb_backend.utils.parse_uri`.
+- Added ``django_mongodb_backend.routers.MongoRouter`` to allow
+  :djadmin:`dumpdata` to ignore embedded models. See
+  :ref:`configuring-database-routers-setting`.
 
 5.0.0 beta 0
 ============

docs/source/releases/5.1.x.rst

@@ -17,6 +17,9 @@ Django MongoDB Backend 5.1.x
 - Added :doc:`async <django:topics/async>` support.
 - Added the ``db_name`` parameter to
   :func:`~django_mongodb_backend.utils.parse_uri`.
+- Added ``django_mongodb_backend.routers.MongoRouter`` to allow
+  :djadmin:`dumpdata` to ignore embedded models. See
+  :ref:`configuring-database-routers-setting`.
 
 5.1.0 beta 0
 ============

tests/models_/models.py

@@ -1,5 +1,11 @@
+from django.db import models
+
 from django_mongodb_backend.models import EmbeddedModel
 
 
 class Embed(EmbeddedModel):
     pass
+
+
+class PlainModel(models.Model):
+    pass

tests/models_/test_routers.py

@@ -0,0 +1,20 @@
+from django.test import SimpleTestCase
+
+from django_mongodb_backend.routers import MongoRouter
+
+
+class TestRouter(SimpleTestCase):
+    def setUp(self):
+        self.router = MongoRouter()
+
+    def test_no_model(self):
+        self.assertIsNone(self.router.allow_migrate("db", "models_"))
+
+    def test_regular_model(self):
+        self.assertIsNone(self.router.allow_migrate("db", "models_", "plainmodel"))
+
+    def test_nonexistent_model(self):
+        self.assertIsNone(self.router.allow_migrate("db", "models_", "nonexistentmodel"))
+
+    def test_embedded_model(self):
+        self.assertIs(self.router.allow_migrate("db", "models_", "embed"), False)