[1.8.x] Fixed #24817 -- Prevented loss of null info in MySQL field renaming.

Backport of 80ad5472ce from master

django/db/backends/base/schema.py

@@ -544,12 +544,7 @@ class BaseDatabaseSchemaEditor(object):
                 self.execute(self._delete_constraint_sql(self.sql_delete_check, model, constraint_name))
         # Have they renamed the column?
         if old_field.column != new_field.column:
-            self.execute(self.sql_rename_column % {
+            self.execute(self._rename_field_sql(model._meta.db_table, old_field, new_field, new_type))
-                "table": self.quote_name(model._meta.db_table),
-                "old_column": self.quote_name(old_field.column),
-                "new_column": self.quote_name(new_field.column),
-                "type": new_type,
-            })
         # Next, start accumulating actions to do
         actions = []
         null_actions = []
@@ -866,6 +861,14 @@ class BaseDatabaseSchemaEditor(object):
             output.append(self._create_index_sql(model, fields, suffix="_idx"))
         return output
 
+    def _rename_field_sql(self, table, old_field, new_field, new_type):
+        return self.sql_rename_column % {
+            "table": self.quote_name(table),
+            "old_column": self.quote_name(old_field.column),
+            "new_column": self.quote_name(new_field.column),
+            "type": new_type,
+        }
+
     def _create_fk_sql(self, model, field, suffix):
         from_table = model._meta.db_table
         from_column = field.column

django/db/backends/mysql/schema.py

@@ -80,10 +80,21 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                 )
         return super(DatabaseSchemaEditor, self)._delete_composed_index(model, fields, *args)
 
-    def _alter_column_type_sql(self, table, old_field, new_field, new_type):
+    def _set_field_new_type_null_status(self, field, new_type):
-        # Keep null property of old field, if it has changed, it will be handled separately
+        """
-        if old_field.null:
+        Keep the null property of the old field. If it has changed, it will be
+        handled separately.
+        """
+        if field.null:
             new_type += " NULL"
         else:
             new_type += " NOT NULL"
+        return new_type
+
+    def _alter_column_type_sql(self, table, old_field, new_field, new_type):
+        new_type = self._set_field_new_type_null_status(old_field, new_type)
         return super(DatabaseSchemaEditor, self)._alter_column_type_sql(table, old_field, new_field, new_type)
+
+    def _rename_field_sql(self, table, old_field, new_field, new_type):
+        new_type = self._set_field_new_type_null_status(old_field, new_type)
+        return super(DatabaseSchemaEditor, self)._rename_field_sql(table, old_field, new_field, new_type)

docs/releases/1.7.9.txt

@@ -0,0 +1,10 @@
+==========================
+Django 1.7.9 release notes
+==========================
+
+*Under development*
+
+Django 1.7.9 fixes several bugs in 1.7.8.
+
+* Prevented the loss of ``null``/``not null`` column properties during field
+  renaming of MySQL databases (:ticket:`24817`).

docs/releases/1.8.3.txt

@@ -25,3 +25,6 @@ Bugfixes
 
 * Fixed a regression which caused template context processors to overwrite
   variables set on a ``RequestContext`` after it's created (:ticket:`24847`).
+
+* Prevented the loss of ``null``/``not null`` column properties during field
+  renaming of MySQL databases (:ticket:`24817`).

docs/releases/index.txt

@@ -35,6 +35,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   1.7.9
    1.7.8
    1.7.7
    1.7.6

tests/schema/models.py

@@ -87,6 +87,14 @@ class Note(models.Model):
         apps = new_apps
 
 
+class NoteRename(models.Model):
+    detail_info = models.TextField()
+
+    class Meta:
+        apps = new_apps
+        db_table = "schema_note"
+
+
 class Tag(models.Model):
     title = models.CharField(max_length=255)
     slug = models.SlugField(unique=True)

tests/schema/tests.py

@@ -20,8 +20,8 @@ from django.test import TransactionTestCase, skipIfDBFeature
 from .fields import CustomManyToManyField, InheritedManyToManyField
 from .models import (
     Author, AuthorWithDefaultHeight, AuthorWithEvenLongerName, Book, BookWeak,
-    BookWithLongName, BookWithO2O, BookWithSlug, Note, Tag, TagIndexed,
+    BookWithLongName, BookWithO2O, BookWithSlug, Note, NoteRename, Tag,
-    TagM2MTest, TagUniqueRename, Thing, UniqueTest, new_apps,
+    TagIndexed, TagM2MTest, TagUniqueRename, Thing, UniqueTest, new_apps,
 )
 
 
@@ -751,6 +751,26 @@ class SchemaTests(TransactionTestCase):
         self.assertEqual(columns['display_name'][0], "CharField")
         self.assertNotIn("name", columns)
 
+    @skipIfDBFeature('interprets_empty_strings_as_nulls')
+    def test_rename_keep_null_status(self):
+        """
+        Renaming a field shouldn't affect the not null status.
+        """
+        with connection.schema_editor() as editor:
+            editor.create_model(Note)
+        with self.assertRaises(IntegrityError):
+            Note.objects.create(info=None)
+        old_field = Note._meta.get_field("info")
+        new_field = TextField()
+        new_field.set_attributes_from_name("detail_info")
+        with connection.schema_editor() as editor:
+            editor.alter_field(Note, old_field, new_field, strict=True)
+        columns = self.column_classes(Note)
+        self.assertEqual(columns['detail_info'][0], "TextField")
+        self.assertNotIn("info", columns)
+        with self.assertRaises(IntegrityError):
+            NoteRename.objects.create(detail_info=None)
+
     def _test_m2m_create(self, M2MFieldClass):
         """
         Tests M2M fields on models during creation