Improve migration optimizer to be able to optimize through other ops

django/db/migrations/operations/base.py

@@ -64,6 +64,18 @@ class Operation(object):
         """
         return "%s: %s" % (self.__class__.__name__, self._constructor_args)
 
+    def references_model(self, name, app_label=None):
+        """
+        Returns True if there is a chance this operation references the given
+        model name (as a string), with an optional app label for accuracy.
+
+        Used for optimization. If in doubt, return True;
+        returning a false positive will merely make the optimizer a little
+        less efficient, while returning a false negative may result in an
+        unusable optimized migration.
+        """
+        return True
+
     def __repr__(self):
         return "<%s %s%s>" % (
             self.__class__.__name__,

django/db/migrations/operations/models.py

@@ -1,4 +1,5 @@
 from .base import Operation
+from django.utils import six
 from django.db import models, router
 from django.db.models.options import normalize_unique_together
 from django.db.migrations.state import ModelState
@@ -33,6 +34,23 @@ class CreateModel(Operation):
     def describe(self):
         return "Create model %s" % (self.name, )
 
+    def references_model(self, name, app_label=None):
+        strings_to_check = [self.name]
+        # Check we didn't inherit from the model
+        for base in self.bases:
+            if isinstance(base, six.string_types):
+                strings_to_check.append(base.split(".")[-1])
+        # Check we have no FKs/M2Ms with it
+        for fname, field in self.fields:
+            if field.rel:
+                if isinstance(field.rel.to, six.string_types):
+                    strings_to_check.append(field.rel.to.split(".")[-1])
+        # Now go over all the strings and compare them
+        for string in strings_to_check:
+            if string.lower() == name.lower():
+                return True
+        return False
+
     def __eq__(self, other):
         return (
             (self.__class__ == other.__class__) and
@@ -66,6 +84,9 @@ class DeleteModel(Operation):
         if router.allow_migrate(schema_editor.connection.alias, model):
             schema_editor.create_model(model)
 
+    def references_model(self, name, app_label=None):
+        return name.lower() == self.name.lower()
+
     def describe(self):
         return "Delete model %s" % (self.name, )
 
@@ -97,6 +118,9 @@ class AlterModelTable(Operation):
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
         return self.database_forwards(app_label, schema_editor, from_state, to_state)
 
+    def references_model(self, name, app_label=None):
+        return name.lower() == self.name.lower()
+
     def describe(self):
         return "Rename table for %s to %s" % (self.name, self.table)
 
@@ -131,6 +155,9 @@ class AlterUniqueTogether(Operation):
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
         return self.database_forwards(app_label, schema_editor, from_state, to_state)
 
+    def references_model(self, name, app_label=None):
+        return name.lower() == self.name.lower()
+
     def describe(self):
         return "Alter unique_together for %s (%s constraints)" % (self.name, len(self.unique_together))
 
@@ -164,5 +191,8 @@ class AlterIndexTogether(Operation):
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
         return self.database_forwards(app_label, schema_editor, from_state, to_state)
 
+    def references_model(self, name, app_label=None):
+        return name.lower() == self.name.lower()
+
     def describe(self):
         return "Alter index_together for %s (%s constraints)" % (self.name, len(self.index_together))