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

Backport of 80ad5472ce from master

django/db/backends/mysql/schema.py

@@ -49,10 +49,21 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                 'column': self.quote_name(field.column),
             }, [effective_default])
 
-    def _alter_column_type_sql(self, table, old_field, new_field, new_type):
-        # Keep null property of old field, if it has changed, it will be handled separately
-        if old_field.null:
+    def _set_field_new_type_null_status(self, field, new_type):
+        """
+        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)

django/db/backends/schema.py

@@ -527,12 +527,7 @@ 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 % {
-                "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,
-            })
+            self.execute(self._rename_field_sql(model._meta.db_table, old_field, new_field, new_type))
         # Next, start accumulating actions to do
         actions = []
         null_actions = []
@@ -841,6 +836,14 @@ 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

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/index.txt

@@ -25,6 +25,7 @@ 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

@@ -122,6 +122,14 @@ class BookWithSlug(models.Model):
         db_table = "schema_book"
 
 
+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

@@ -1,17 +1,27 @@
 import datetime
 import unittest
 
-from django.test import TransactionTestCase, skipIfDBFeature
-from django.db import connection, DatabaseError, IntegrityError, OperationalError
-from django.db.models.fields import (BigIntegerField, BinaryField, BooleanField, CharField,
-    IntegerField, PositiveIntegerField, SlugField, TextField)
-from django.db.models.fields.related import ForeignKey, ManyToManyField, OneToOneField
+from django.db import (
+    DatabaseError, IntegrityError, OperationalError, connection,
+)
+from django.db.models.fields import (
+    BigIntegerField, BinaryField, BooleanField, CharField, IntegerField,
+    PositiveIntegerField, SlugField, TextField,
+)
+from django.db.models.fields.related import (
+    ForeignKey, ManyToManyField, OneToOneField,
+)
 from django.db.transaction import atomic
+from django.test import TransactionTestCase, skipIfDBFeature
+
 from .fields import CustomManyToManyField, InheritedManyToManyField
-from .models import (Author, AuthorWithDefaultHeight, AuthorWithM2M, Book, BookWithLongName,
-    BookWithSlug, BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename,
-    UniqueTest, Thing, TagThrough, BookWithM2MThrough, AuthorTag, AuthorWithM2MThrough,
-    AuthorWithEvenLongerName, BookWeak, Note, BookWithO2O, BookWithoutFK)
+from .models import (
+    Author, AuthorTag, AuthorWithDefaultHeight, AuthorWithEvenLongerName,
+    AuthorWithM2M, AuthorWithM2MThrough, Book, BookWeak, BookWithLongName,
+    BookWithM2M, BookWithM2MThrough, BookWithO2O, BookWithoutFK, BookWithSlug,
+    Note, NoteRename, Tag, TagIndexed, TagM2MTest, TagThrough, TagUniqueRename,
+    Thing, UniqueTest,
+)
 
 
 class SchemaTests(TransactionTestCase):
@@ -754,6 +764,26 @@ 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):
         """
         Tests M2M fields on models during creation