Implement get_view_str approach.

A couple of other changes:

* AppRegistryNotReady fix (via both imports changes and docs update).
* Non-flat models structure support (app.models.submodels.Model).
* Minor refactoring.

dbview/__init__.py

@@ -1,3 +0,0 @@
-# placeholder for git
-from dbview.helpers import CreateView
-from dbview.models import DbView

dbview/helpers.py

@@ -1,42 +1,64 @@
+import logging
+
 from django.db import migrations
 from django.apps import apps
 
 
 class CreateView(migrations.CreateModel):
+
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        model = to_state.apps.get_model(app_label, self.name)
+        fake_model = to_state.apps.get_model(app_label, self.name)
 
-        if not self.allow_migrate_model(schema_editor.connection.alias, model):
+        if not self.allow_migrate_model(
+                schema_editor.connection.alias, fake_model):
             raise
-        models = apps.get_app_config(app_label).models_module
-        model = getattr(models, self.name)
 
-        sql = 'DROP VIEW IF EXISTS %(table)s;'
+        model = self._get_model(fake_model, app_label, to_state)
 
-        args = {
-            'table' : schema_editor.quote_name(model._meta.db_table),
-        }
-
-        sql = sql % args
-
-        schema_editor.execute(sql, None)
-
-        sql = 'CREATE VIEW %(table)s AS %(definition)s'
+        self._drop_view(fake_model, schema_editor)
 
         if hasattr(model, 'view'):
-            qs = str(model.view())
+            self._create_standard_view(model, schema_editor)
+        elif hasattr(model, 'get_view_str'):
+            self._create_view_from_raw_sql(model.get_view_str(), schema_editor)
         else:
-            raise Exception('Your view needs to define either view or ' +
-                            'get_view_str')
-
-        args['definition'] = qs
-
-        sql = sql % args
-
-        schema_editor.execute(sql, None)
+            raise Exception(f"{model} has neither view nor get_view_str")
 
     def database_backwards(self, app_label, schema_editor, from_state, to):
-        model = from_state.apps.get_model(app_label, self.name)
-        sql = 'DROP VIEW IF EXISTS %s' % \
-              schema_editor.quote_name(model._meta.db_table)
+        fake_model = from_state.apps.get_model(app_label, self.name)
+        self._drop_view(fake_model, schema_editor)
+
+    def _get_model(self, state, app_label, fake_model):
+        models = apps.get_app_config(app_label).models_module
+
+        if hasattr(models, self.name):
+            return getattr(models, self.name)
+
+        # TODO: recursive search
+        for submodule in models.__dict__.values():
+            if hasattr(submodule, self.name):
+                return getattr(submodule, self.name)
+
+        logging.warning('Using fake model, this may fail with inherited views')
+        return fake_model
+
+    def _drop_view(self, model, schema_editor):
+        sql_template = 'DROP VIEW IF EXISTS %(table)s CASCADE'
+        args = {
+            'table': schema_editor.quote_name(model._meta.db_table),
+        }
+        sql = sql_template % args
+        schema_editor.execute(sql, None)
+
+    def _create_standard_view(self, model, schema_editor):
+        sql_template = 'CREATE VIEW %(table)s AS %(definition)s'
+        qs = str(model.view())
+        args = {
+            'table': schema_editor.quote_name(model._meta.db_table),
+            'definition': qs,
+        }
+        sql = sql_template % args
+        self._create_view_from_raw_sql(sql, schema_editor)
+
+    def _create_view_from_raw_sql(self, sql, schema_editor):
         schema_editor.execute(sql, None)