Replaced migration state render() by apps cached property

Refs #23745.

6 files changed, 99 insertions, 106 deletions

diff --git a/django/db/migrations/autodetector.py b/django/db/migrations/autodetector.py
index 440b83880c..d96f09b0be 100644
--- a/django/db/migrations/autodetector.py
+++ b/django/db/migrations/autodetector.py
@@ -108,8 +108,8 @@ class MigrationAutodetector(object):
 
         # Prepare some old/new state and model lists, separating
         # proxy models and ignoring unmigrated apps.
-        self.old_apps = self.from_state.render(ignore_swappable=True)
-        self.new_apps = self.to_state.render()
+        self.old_apps = self.from_state.apps
+        self.new_apps = self.to_state.apps
         self.old_model_keys = []
         self.old_proxy_keys = []
         self.old_unmanaged_keys = []
diff --git a/django/db/migrations/executor.py b/django/db/migrations/executor.py
index f5811bb795..4a73546ba8 100644
--- a/django/db/migrations/executor.py
+++ b/django/db/migrations/executor.py
@@ -137,7 +137,7 @@ class MigrationExecutor(object):
         on initial migrations (as it only looks for CreateModel).
         """
         project_state = self.loader.project_state((migration.app_label, migration.name), at_end=True)
-        apps = project_state.render()
+        apps = project_state.apps
         found_create_migration = False
         # Bail if the migration isn't the first one in its app
         if [name for app, name in migration.dependencies if app == migration.app_label]:
diff --git a/django/db/migrations/operations/fields.py b/django/db/migrations/operations/fields.py
index fd3f62de1f..ba123de9c3 100644
--- a/django/db/migrations/operations/fields.py
+++ b/django/db/migrations/operations/fields.py
@@ -40,9 +40,9 @@ class AddField(Operation):
         state.models[app_label, self.model_name.lower()].fields.append((self.name, field))
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        to_model = to_state.render().get_model(app_label, self.model_name)
+        to_model = to_state.apps.get_model(app_label, self.model_name)
         if self.allowed_to_migrate(schema_editor.connection.alias, to_model):
-            from_model = from_state.render().get_model(app_label, self.model_name)
+            from_model = from_state.apps.get_model(app_label, self.model_name)
             field = to_model._meta.get_field_by_name(self.name)[0]
             if not self.preserve_default:
                 field.default = self.field.default
@@ -54,7 +54,7 @@ class AddField(Operation):
                 field.default = NOT_PROVIDED
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
-        from_model = from_state.render().get_model(app_label, self.model_name)
+        from_model = from_state.apps.get_model(app_label, self.model_name)
         if self.allowed_to_migrate(schema_editor.connection.alias, from_model):
             schema_editor.remove_field(from_model, from_model._meta.get_field_by_name(self.name)[0])
 
@@ -96,14 +96,14 @@ class RemoveField(Operation):
         state.models[app_label, self.model_name.lower()].fields = new_fields
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        from_model = from_state.render().get_model(app_label, self.model_name)
+        from_model = from_state.apps.get_model(app_label, self.model_name)
         if self.allowed_to_migrate(schema_editor.connection.alias, from_model):
             schema_editor.remove_field(from_model, from_model._meta.get_field_by_name(self.name)[0])
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
-        to_model = to_state.render().get_model(app_label, self.model_name)
+        to_model = to_state.apps.get_model(app_label, self.model_name)
         if self.allowed_to_migrate(schema_editor.connection.alias, to_model):
-            from_model = from_state.render().get_model(app_label, self.model_name)
+            from_model = from_state.apps.get_model(app_label, self.model_name)
             schema_editor.add_field(from_model, to_model._meta.get_field_by_name(self.name)[0])
 
     def describe(self):
@@ -152,9 +152,9 @@ class AlterField(Operation):
         ]
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        to_model = to_state.render().get_model(app_label, self.model_name)
+        to_model = to_state.apps.get_model(app_label, self.model_name)
         if self.allowed_to_migrate(schema_editor.connection.alias, to_model):
-            from_model = from_state.render().get_model(app_label, self.model_name)
+            from_model = from_state.apps.get_model(app_label, self.model_name)
             from_field = from_model._meta.get_field_by_name(self.name)[0]
             to_field = to_model._meta.get_field_by_name(self.name)[0]
             # If the field is a relatedfield with an unresolved rel.to, just
@@ -222,9 +222,9 @@ class RenameField(Operation):
                 ]
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        to_model = to_state.render().get_model(app_label, self.model_name)
+        to_model = to_state.apps.get_model(app_label, self.model_name)
         if self.allowed_to_migrate(schema_editor.connection.alias, to_model):
-            from_model = from_state.render().get_model(app_label, self.model_name)
+            from_model = from_state.apps.get_model(app_label, self.model_name)
             schema_editor.alter_field(
                 from_model,
                 from_model._meta.get_field_by_name(self.old_name)[0],
@@ -232,9 +232,9 @@ class RenameField(Operation):
             )
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
-        to_model = to_state.render().get_model(app_label, self.model_name)
+        to_model = to_state.apps.get_model(app_label, self.model_name)
         if self.allowed_to_migrate(schema_editor.connection.alias, to_model):
-            from_model = from_state.render().get_model(app_label, self.model_name)
+            from_model = from_state.apps.get_model(app_label, self.model_name)
             schema_editor.alter_field(
                 from_model,
                 from_model._meta.get_field_by_name(self.new_name)[0],
diff --git a/django/db/migrations/operations/models.py b/django/db/migrations/operations/models.py
index 2436701919..eda30f88e8 100644
--- a/django/db/migrations/operations/models.py
+++ b/django/db/migrations/operations/models.py
@@ -49,14 +49,12 @@ class CreateModel(Operation):
         )
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        apps = to_state.render()
-        model = apps.get_model(app_label, self.name)
+        model = to_state.apps.get_model(app_label, self.name)
         if self.allowed_to_migrate(schema_editor.connection.alias, model):
             schema_editor.create_model(model)
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
-        apps = from_state.render()
-        model = apps.get_model(app_label, self.name)
+        model = from_state.apps.get_model(app_label, self.name)
         if self.allowed_to_migrate(schema_editor.connection.alias, model):
             schema_editor.delete_model(model)
 
@@ -103,14 +101,12 @@ class DeleteModel(Operation):
         del state.models[app_label, self.name.lower()]
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        apps = from_state.render()
-        model = apps.get_model(app_label, self.name)
+        model = from_state.apps.get_model(app_label, self.name)
         if self.allowed_to_migrate(schema_editor.connection.alias, model):
             schema_editor.delete_model(model)
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
-        apps = to_state.render()
-        model = apps.get_model(app_label, self.name)
+        model = to_state.apps.get_model(app_label, self.name)
         if self.allowed_to_migrate(schema_editor.connection.alias, model):
             schema_editor.create_model(model)
 
@@ -143,7 +139,7 @@ class RenameModel(Operation):
 
     def state_forwards(self, app_label, state):
         # Get all of the related objects we need to repoint
-        apps = state.render(skip_cache=True)
+        apps = state.apps
         model = apps.get_model(app_label, self.old_name)
         related_objects = model._meta.get_all_related_objects()
         related_m2m_objects = model._meta.get_all_related_many_to_many_objects()
@@ -168,13 +164,12 @@ class RenameModel(Operation):
                     field.rel.to = "%s.%s" % (app_label, self.new_name)
                 new_fields.append((name, field))
             state.models[related_key].fields = new_fields
+        del state.apps  # FIXME: this should be replaced by a logic in state (update_model?)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        new_apps = to_state.render()
-        new_model = new_apps.get_model(app_label, self.new_name)
+        new_model = to_state.apps.get_model(app_label, self.new_name)
         if self.allowed_to_migrate(schema_editor.connection.alias, new_model):
-            old_apps = from_state.render()
-            old_model = old_apps.get_model(app_label, self.old_name)
+            old_model = from_state.apps.get_model(app_label, self.old_name)
             # Move the main table
             schema_editor.alter_db_table(
                 new_model,
@@ -194,7 +189,7 @@ class RenameModel(Operation):
                         related_object.model._meta.app_label,
                         related_object.model._meta.object_name.lower(),
                     )
-                to_field = new_apps.get_model(
+                to_field = to_state.apps.get_model(
                     *related_key
                 )._meta.get_field_by_name(related_object.field.name)[0]
                 schema_editor.alter_field(
@@ -242,11 +237,9 @@ class AlterModelTable(Operation):
         state.models[app_label, self.name.lower()].options["db_table"] = self.table
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        new_apps = to_state.render()
-        new_model = new_apps.get_model(app_label, self.name)
+        new_model = to_state.apps.get_model(app_label, self.name)
         if self.allowed_to_migrate(schema_editor.connection.alias, new_model):
-            old_apps = from_state.render()
-            old_model = old_apps.get_model(app_label, self.name)
+            old_model = from_state.apps.get_model(app_label, self.name)
             schema_editor.alter_db_table(
                 new_model,
                 old_model._meta.db_table,
@@ -299,11 +292,9 @@ class AlterUniqueTogether(Operation):
         model_state.options[self.option_name] = self.unique_together
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        new_apps = to_state.render()
-        new_model = new_apps.get_model(app_label, self.name)
+        new_model = to_state.apps.get_model(app_label, self.name)
         if self.allowed_to_migrate(schema_editor.connection.alias, new_model):
-            old_apps = from_state.render()
-            old_model = old_apps.get_model(app_label, self.name)
+            old_model = from_state.apps.get_model(app_label, self.name)
             schema_editor.alter_unique_together(
                 new_model,
                 getattr(old_model._meta, self.option_name, set()),
@@ -348,11 +339,9 @@ class AlterIndexTogether(Operation):
         model_state.options[self.option_name] = self.index_together
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        new_apps = to_state.render()
-        new_model = new_apps.get_model(app_label, self.name)
+        new_model = to_state.apps.get_model(app_label, self.name)
         if self.allowed_to_migrate(schema_editor.connection.alias, new_model):
-            old_apps = from_state.render()
-            old_model = old_apps.get_model(app_label, self.name)
+            old_model = from_state.apps.get_model(app_label, self.name)
             schema_editor.alter_index_together(
                 new_model,
                 getattr(old_model._meta, self.option_name, set()),
@@ -394,9 +383,9 @@ class AlterOrderWithRespectTo(Operation):
         model_state.options['order_with_respect_to'] = self.order_with_respect_to
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        to_model = to_state.render().get_model(app_label, self.name)
+        to_model = to_state.apps.get_model(app_label, self.name)
         if self.allowed_to_migrate(schema_editor.connection.alias, to_model):
-            from_model = from_state.render().get_model(app_label, self.name)
+            from_model = from_state.apps.get_model(app_label, self.name)
             # Remove a field if we need to
             if from_model._meta.order_with_respect_to and not to_model._meta.order_with_respect_to:
                 schema_editor.remove_field(from_model, from_model._meta.get_field_by_name("_order")[0])
diff --git a/django/db/migrations/operations/special.py b/django/db/migrations/operations/special.py
index c7d438c2a0..96fd2cc63c 100644
--- a/django/db/migrations/operations/special.py
+++ b/django/db/migrations/operations/special.py
@@ -166,12 +166,12 @@ class RunPython(Operation):
         # object, representing the versioned models as an app registry.
         # We could try to override the global cache, but then people will still
         # use direct imports, so we go with a documentation approach instead.
-        self.code(from_state.render(), schema_editor)
+        self.code(from_state.apps, schema_editor)
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
         if self.reverse_code is None:
             raise NotImplementedError("You cannot reverse this operation")
-        self.reverse_code(from_state.render(), schema_editor)
+        self.reverse_code(from_state.apps, schema_editor)
 
     def describe(self):
         return "Raw Python operation"
diff --git a/django/db/migrations/state.py b/django/db/migrations/state.py
index 871e9920fa..f2267b3536 100644
--- a/django/db/migrations/state.py
+++ b/django/db/migrations/state.py
@@ -9,6 +9,7 @@ from django.db.models.fields.proxy import OrderWrt
 from django.conf import settings
 from django.utils import six
 from django.utils.encoding import force_text, smart_text
+from django.utils.functional import cached_property
 from django.utils.module_loading import import_string
 from django.utils.version import get_docs_version
 
@@ -26,7 +27,6 @@ class ProjectState(object):
 
     def __init__(self, models=None, real_apps=None):
         self.models = models or {}
-        self.apps = None
         # Apps to include from main registry, usually unmigrated ones
         self.real_apps = real_apps or []
 
@@ -40,66 +40,9 @@ class ProjectState(object):
             real_apps=self.real_apps,
         )
 
-    def render(self, include_real=None, ignore_swappable=False, skip_cache=False):
-        "Turns the project state into actual models in a new Apps"
-        if self.apps is None or skip_cache:
-            # Any apps in self.real_apps should have all their models included
-            # in the render. We don't use the original model instances as there
-            # are some variables that refer to the Apps object.
-            # FKs/M2Ms from real apps are also not included as they just
-            # mess things up with partial states (due to lack of dependencies)
-            real_models = []
-            for app_label in self.real_apps:
-                app = global_apps.get_app_config(app_label)
-                for model in app.get_models():
-                    real_models.append(ModelState.from_model(model, exclude_rels=True))
-            # Populate the app registry with a stub for each application.
-            app_labels = set(model_state.app_label for model_state in self.models.values())
-            self.apps = Apps([AppConfigStub(label) for label in sorted(self.real_apps + list(app_labels))])
-            # We keep trying to render the models in a loop, ignoring invalid
-            # base errors, until the size of the unrendered models doesn't
-            # decrease by at least one, meaning there's a base dependency loop/
-            # missing base.
-            unrendered_models = list(self.models.values()) + real_models
-            while unrendered_models:
-                new_unrendered_models = []
-                for model in unrendered_models:
-                    try:
-                        model.render(self.apps)
-                    except InvalidBasesError:
-                        new_unrendered_models.append(model)
-                if len(new_unrendered_models) == len(unrendered_models):
-                    raise InvalidBasesError(
-                        "Cannot resolve bases for %r\nThis can happen if you are inheriting models from an "
-                        "app with migrations (e.g. contrib.auth)\n in an app with no migrations; see "
-                        "https://docs.djangoproject.com/en/%s/topics/migrations/#dependencies "
-                        "for more" % (new_unrendered_models, get_docs_version())
-                    )
-                unrendered_models = new_unrendered_models
-            # make sure apps has no dangling references
-            if self.apps._pending_lookups:
-                # There's some lookups left. See if we can first resolve them
-                # ourselves - sometimes fields are added after class_prepared is sent
-                for lookup_model, operations in self.apps._pending_lookups.items():
-                    try:
-                        model = self.apps.get_model(lookup_model[0], lookup_model[1])
-                    except LookupError:
-                        app_label = "%s.%s" % (lookup_model[0], lookup_model[1])
-                        if app_label == settings.AUTH_USER_MODEL and ignore_swappable:
-                            continue
-                        # Raise an error with a best-effort helpful message
-                        # (only for the first issue). Error message should look like:
-                        # "ValueError: Lookup failed for model referenced by
-                        # field migrations.Book.author: migrations.Author"
-                        msg = "Lookup failed for model referenced by field {field}: {model[0]}.{model[1]}"
-                        raise ValueError(msg.format(field=operations[0][1], model=lookup_model))
-                    else:
-                        do_pending_lookups(model)
-        try:
-            return self.apps
-        finally:
-            if skip_cache:
-                self.apps = None
+    @cached_property
+    def apps(self):
+        return StateApps(self.real_apps, self.models)
 
     @classmethod
     def from_apps(cls, apps):
@@ -139,6 +82,67 @@ class AppConfigStub(AppConfig):
         self.models = all_models
 
 
+class StateApps(Apps):
+    """
+    Subclass of the global Apps registry class to better handle dynamic model
+    additions and removals.
+    """
+    def __init__(self, real_apps, models):
+        # Any apps in self.real_apps should have all their models included
+        # in the render. We don't use the original model instances as there
+        # are some variables that refer to the Apps object.
+        # FKs/M2Ms from real apps are also not included as they just
+        # mess things up with partial states (due to lack of dependencies)
+        real_models = []
+        for app_label in real_apps:
+            app = global_apps.get_app_config(app_label)
+            for model in app.get_models():
+                real_models.append(ModelState.from_model(model, exclude_rels=True))
+        # Populate the app registry with a stub for each application.
+        app_labels = {model_state.app_label for model_state in models.values()}
+        app_configs = [AppConfigStub(label) for label in sorted(real_apps + list(app_labels))]
+        super(StateApps, self).__init__(app_configs)
+
+        # We keep trying to render the models in a loop, ignoring invalid
+        # base errors, until the size of the unrendered models doesn't
+        # decrease by at least one, meaning there's a base dependency loop/
+        # missing base.
+        unrendered_models = list(models.values()) + real_models
+        while unrendered_models:
+            new_unrendered_models = []
+            for model in unrendered_models:
+                try:
+                    model.render(self)
+                except InvalidBasesError:
+                    new_unrendered_models.append(model)
+            if len(new_unrendered_models) == len(unrendered_models):
+                raise InvalidBasesError(
+                    "Cannot resolve bases for %r\nThis can happen if you are inheriting models from an "
+                    "app with migrations (e.g. contrib.auth)\n in an app with no migrations; see "
+                    "https://docs.djangoproject.com/en/%s/topics/migrations/#dependencies "
+                    "for more" % (new_unrendered_models, get_docs_version())
+                )
+            unrendered_models = new_unrendered_models
+
+        # If there are some lookups left, see if we can first resolve them
+        # ourselves - sometimes fields are added after class_prepared is sent
+        for lookup_model, operations in self._pending_lookups.items():
+            try:
+                model = self.get_model(lookup_model[0], lookup_model[1])
+            except LookupError:
+                app_label = "%s.%s" % (lookup_model[0], lookup_model[1])
+                if app_label == settings.AUTH_USER_MODEL and ignore_swappable:
+                    continue
+                # Raise an error with a best-effort helpful message
+                # (only for the first issue). Error message should look like:
+                # "ValueError: Lookup failed for model referenced by
+                # field migrations.Book.author: migrations.Author"
+                msg = "Lookup failed for model referenced by field {field}: {model[0]}.{model[1]}"
+                raise ValueError(msg.format(field=operations[0][1], model=lookup_model))
+            else:
+                do_pending_lookups(model)
+
+
 class ModelState(object):
     """
     Represents a Django Model. We don't use the actual Model class