Add AlterField and RenameField operations

3 files changed, 77 insertions, 2 deletions

diff --git a/django/db/migrations/operations/__init__.py b/django/db/migrations/operations/__init__.py
index 6c2c784635..925b05fff3 100644
--- a/django/db/migrations/operations/__init__.py
+++ b/django/db/migrations/operations/__init__.py
@@ -1,2 +1,2 @@
 from .models import CreateModel, DeleteModel, AlterModelTable
-from .fields import AddField, RemoveField
+from .fields import AddField, RemoveField, AlterField, RenameField
diff --git a/django/db/migrations/operations/fields.py b/django/db/migrations/operations/fields.py
index 660cba6b72..cc4f4a43df 100644
--- a/django/db/migrations/operations/fields.py
+++ b/django/db/migrations/operations/fields.py
@@ -54,3 +54,71 @@ class RemoveField(Operation):
 
     def describe(self):
         return "Remove field %s from %s" % (self.name, self.model_name)
+
+
+class AlterField(Operation):
+    """
+    Alters a field's database column (e.g. null, max_length) to the provided new field
+    """
+
+    def __init__(self, model_name, name, field):
+        self.model_name = model_name
+        self.name = name
+        self.field = field
+
+    def state_forwards(self, app_label, state):
+        state.models[app_label, self.model_name.lower()].fields = [
+            (n, self.field if n == self.name else f) for n, f in state.models[app_label, self.model_name.lower()].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)
+        to_model = to_state.render().get_model(app_label, self.model_name)
+        schema_editor.alter_field(
+            from_model,
+            from_model._meta.get_field_by_name(self.name)[0],
+            to_model._meta.get_field_by_name(self.name)[0],
+        )
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        self.database_forwards(app_label, schema_editor, from_state, to_state)
+
+    def describe(self):
+        return "Alter field %s on %s" % (self.name, self.model_name)
+
+
+class RenameField(Operation):
+    """
+    Renames a field on the model. Might affect db_column too.
+    """
+
+    def __init__(self, model_name, old_name, new_name):
+        self.model_name = model_name
+        self.old_name = old_name
+        self.new_name = new_name
+
+    def state_forwards(self, app_label, state):
+        state.models[app_label, self.model_name.lower()].fields = [
+            (self.new_name if n == self.old_name else n, f) for n, f in state.models[app_label, self.model_name.lower()].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)
+        to_model = to_state.render().get_model(app_label, self.model_name)
+        schema_editor.alter_field(
+            from_model,
+            from_model._meta.get_field_by_name(self.old_name)[0],
+            to_model._meta.get_field_by_name(self.new_name)[0],
+        )
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        from_model = from_state.render().get_model(app_label, self.model_name)
+        to_model = to_state.render().get_model(app_label, self.model_name)
+        schema_editor.alter_field(
+            from_model,
+            from_model._meta.get_field_by_name(self.new_name)[0],
+            to_model._meta.get_field_by_name(self.old_name)[0],
+        )
+
+    def describe(self):
+        return "Rename field %s on %s to %s" % (self.old_name, self.model_name, self.new_name)
diff --git a/django/db/migrations/state.py b/django/db/migrations/state.py
index b6618041f2..65b749c80c 100644
--- a/django/db/migrations/state.py
+++ b/django/db/migrations/state.py
@@ -93,10 +93,17 @@ class ModelState(object):
 
     def clone(self):
         "Returns an exact copy of this ModelState"
+        # We deep-clone the fields using deconstruction
+        fields = []
+        for name, field in self.fields:
+            _, path, args, kwargs = field.deconstruct()
+            field_class = import_by_path(path)
+            fields.append((name, field_class(*args, **kwargs)))
+        # Now make a copy
         return self.__class__(
             app_label = self.app_label,
             name = self.name,
-            fields = list(self.fields),
+            fields = fields,
             options = dict(self.options),
             bases = self.bases,
         )