Ticket #697: south-0.7-697.diff

south/db/generic.py

@@ -657 +657 @@
 
     drop_index = alias('delete_index')
 
+    def delete_foreign_key_by_keyname(self, table_name, foreign_key_name):
+        """
+        Drop a foreign key constraint by name
+        """
+        if self.dry_run:
+            return # We can't look at the DB to get the constraints
+        self.execute(self.delete_foreign_key_sql % {
+            "table": self.quote_name(table_name),
+            "constraint": self.quote_name(foreign_key_name),
+        })
 
     def delete_column(self, table_name, name):
         """

south/db/mysql.py

@@ -63 +63 @@
             rows[0][5] or "",
         )
         
+        # migrate any foreign keys
+        fks_to_reinstate = self._get_all_fks(table_name)
+        for constraint in fks_to_reinstate:
+            if (fks_to_reinstate[constraint]['column'] == old):
+                # delete any applicable foreign keys            
+                self.delete_foreign_key_by_keyname(table_name, fks_to_reinstate[constraint]['name'])
+            
         sql = 'ALTER TABLE %s CHANGE COLUMN %s %s %s %s %s %s %s;' % params
         
         if rows[0][4]:
             self.execute(sql, (rows[0][4],))
         else:
             self.execute(sql)
+            
+        # reinstate the foreign keys to the new mapping
+        for constraint in fks_to_reinstate:
+            if (fks_to_reinstate[constraint]['column'] == old):
+                self.foreign_key_sql(fks_to_reinstate[constraint]['src_table'], fks_to_reinstate[constraint]['src_col'], table_name, new)
     
     
     def delete_column(self, table_name, name):
@@ -107 +119 @@
             # No Operation
             return
         params = (self.quote_name(old_table_name), self.quote_name(table_name))
-        self.execute('RENAME TABLE %s TO %s;' % params)
+        
+        # migrate any foreign keys
+        fks_to_reinstate = self._get_all_fks(old_table_name)
+        for constraint in fks_to_reinstate:
+            # delete any foreign keys
+            self.delete_foreign_key_by_keyname(old_table_name, fks_to_reinstate[constraint]['name'])
+        
+        self.execute('ALTER TABLE %s RENAME TO %s;' % params)
+        
+        # reinstate foreign keys that had to be removed with the table rename operation
+        for constraint in fks_to_reinstate:
+            self.foreign_key_sql(fks_to_reinstate[constraint]['src_table'], fks_to_reinstate[constraint]['src_col'], table_name, fks_to_reinstate[constraint]['column'])
     
+        
+    def _get_all_fks(self, table_name):
+        
+        db_name = self._get_setting('NAME')
+
+        # First, load all constraint->col mappings for this table.
+        sql = """
+        SELECT kc.constraint_name, kc.column_name, kc.referenced_table_name, kc.referenced_column_name
+            FROM information_schema.key_column_usage AS kc
+            JOIN information_schema.table_constraints AS c ON
+                kc.table_schema = c.table_schema AND
+                kc.table_name = c.table_name AND
+                kc.constraint_name = c.constraint_name
+            WHERE
+                kc.table_schema = '%s' AND
+                kc.table_catalog IS NULL AND
+                kc.table_name = '%s' AND
+                c.constraint_type = 'FOREIGN KEY'
+        """    
+        rows = self.execute(sql % (db_name, table_name))
+        
+        # Load into a dict
+        mapping = {}
+        for constraint, column, ref_table, ref_col in rows:
+            #mapping.setdefault(constraint, set())
+            mapping[constraint] = {'name': constraint, 'column': column, 'src_table': ref_table, 'src_col': ref_col}
+            
+        return mapping
     
     def _constraints_affecting_columns(self, table_name, columns, type="UNIQUE"):
         """