Implement primary key changing

django/db/backends/mysql/introspection.py

@@ -99,7 +99,12 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         for row in rows:
             if row[2] in multicol_indexes:
                 continue
-            indexes[row[4]] = {'primary_key': (row[2] == 'PRIMARY'), 'unique': not bool(row[1])}
+            if row[4] not in indexes:
+                indexes[row[4]] = {'primary_key': False, 'unique': False}
+            if row[2] == 'PRIMARY':
+                indexes[row[4]]['primary_key'] = True
+            if not bool(row[1]):
+                indexes[row[4]]['unique'] = True
         return indexes
 
     def get_constraints(self, cursor, table_name):

django/db/backends/mysql/schema.py

@@ -21,3 +21,6 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
 
     alter_string_set_null = 'MODIFY %(column)s %(type)s NULL;'
     alter_string_drop_null = 'MODIFY %(column)s %(type)s NOT NULL;'
+
+    sql_create_pk = "ALTER TABLE %(table)s ADD CONSTRAINT %(name)s PRIMARY KEY (%(columns)s)"
+    sql_delete_pk = "ALTER TABLE %(table)s DROP PRIMARY KEY"

django/db/backends/schema.py

@@ -24,8 +24,6 @@ class BaseDatabaseSchemaEditor(object):
         - Repointing of FKs
         - Repointing of M2Ms
         - Check constraints (PosIntField)
-        - PK changing
-        - db_index on alter field
     """
 
     # Overrideable SQL templates
@@ -57,8 +55,8 @@ class BaseDatabaseSchemaEditor(object):
     sql_create_index = "CREATE INDEX %(name)s ON %(table)s (%(columns)s)%(extra)s;"
     sql_delete_index = "DROP INDEX %(name)s"
 
-    sql_create_pk = "ALTER TABLE %(table)s ADD CONSTRAINT %(constraint)s PRIMARY KEY (%(columns)s)"
+    sql_create_pk = "ALTER TABLE %(table)s ADD CONSTRAINT %(name)s PRIMARY KEY (%(columns)s)"
-    sql_delete_pk = "ALTER TABLE %(table)s DROP CONSTRAINT %(constraint)s"
+    sql_delete_pk = "ALTER TABLE %(table)s DROP CONSTRAINT %(name)s"
 
     def __init__(self, connection):
         self.connection = connection
@@ -135,9 +133,10 @@ class BaseDatabaseSchemaEditor(object):
         elif field.unique:
             sql += " UNIQUE"
         # If we were told to include a default value, do so
-        if include_default:
+        default_value = self.effective_default(field)
+        if include_default and default_value is not None:
             sql += " DEFAULT %s"
-            params += [self.effective_default(field)]
+            params += [default_value]
         # Return the sql
         return sql, params
 
@@ -491,6 +490,32 @@ class BaseDatabaseSchemaEditor(object):
                     "extra": "",
                 }
             )
+        # Changed to become primary key?
+        # Note that we don't detect unsetting of a PK, as we assume another field
+        # will always come along and replace it.
+        if not old_field.primary_key and new_field.primary_key:
+            # First, drop the old PK
+            constraint_names = self._constraint_names(model, primary_key=True)
+            if strict and len(constraint_names) != 1:
+                raise ValueError("Found wrong number (%s) of PK constraints for %s" % (
+                    len(constraint_names),
+                    model._meta.db_table,
+                ))
+            for constraint_name in constraint_names:
+                self.execute(
+                    self.sql_delete_pk % {
+                        "table": self.quote_name(model._meta.db_table),
+                        "name": constraint_name,
+                    },
+                )
+            # Make the new one
+            self.execute(
+                self.sql_create_pk % {
+                    "table": self.quote_name(model._meta.db_table),
+                    "name": self._create_index_name(model, [new_field.column], suffix="_pk"),
+                    "columns": self.quote_name(new_field.column),
+                }
+            )
 
     def _type_for_alter(self, field):
         """
@@ -518,16 +543,16 @@ class BaseDatabaseSchemaEditor(object):
             index_name = '%s%s' % (table_name[:(self.connection.features.max_index_name_length - len(part))], part)
         return index_name
 
-    def _constraint_names(self, model, column_names, unique=None, primary_key=None, index=None):
+    def _constraint_names(self, model, column_names=None, unique=None, primary_key=None, index=None):
         "Returns all constraint names matching the columns and conditions"
-        column_names = set(column_names)
+        column_names = set(column_names) if column_names else None
         constraints = self.connection.introspection.get_constraints(self.connection.cursor(), model._meta.db_table)
         result = []
         for name, infodict in constraints.items():
-            if column_names == infodict['columns']:
+            if column_names is None or column_names == infodict['columns']:
                 if unique is not None and infodict['unique'] != unique:
                     continue
-                if primary_key is not None and infodict['primary_key'] != unique:
+                if primary_key is not None and infodict['primary_key'] != primary_key:
                     continue
                 if index is not None and infodict['index'] != index:
                     continue

tests/modeltests/schema/tests.py

@@ -478,3 +478,37 @@ class SchemaTests(TestCase):
             "slug",
             connection.introspection.get_indexes(connection.cursor(), Book._meta.db_table),
         )
+
+    def test_primary_key(self):
+        """
+        Tests altering of the primary key
+        """
+        # Create the table
+        editor = connection.schema_editor()
+        editor.start()
+        editor.create_model(Tag)
+        editor.commit()
+        # Ensure the table is there and has the right PK
+        self.assertTrue(
+            connection.introspection.get_indexes(connection.cursor(), Tag._meta.db_table)['id']['primary_key'],
+        )
+        # Alter to change the PK
+        new_field = SlugField(primary_key=True)
+        new_field.set_attributes_from_name("slug")
+        editor = connection.schema_editor()
+        editor.start()
+        editor.delete_field(Tag, Tag._meta.get_field_by_name("id")[0])
+        editor.alter_field(
+            Tag,
+            Tag._meta.get_field_by_name("slug")[0],
+            new_field,
+        )
+        editor.commit()
+        # Ensure the PK changed
+        self.assertNotIn(
+            'id',
+            connection.introspection.get_indexes(connection.cursor(), Tag._meta.db_table),
+        )
+        self.assertTrue(
+            connection.introspection.get_indexes(connection.cursor(), Tag._meta.db_table)['slug']['primary_key'],
+        )