+def column_set_from_json(json, columns):
+ if json is None:
+ return tuple(columns)
+ elif type(json) != list:
+ raise error.Error("array of distinct column names expected", json)
+ else:
+ for column_name in json:
+ if type(column_name) not in [str, unicode]:
+ raise error.Error("array of distinct column names expected",
+ json)
+ elif column_name not in columns:
+ raise error.Error("%s is not a valid column name"
+ % column_name, json)
+ if len(set(json)) != len(json):
+ # Duplicate.
+ raise error.Error("array of distinct column names expected", json)
+ return tuple([columns[column_name] for column_name in json])
+