code: function(db_schema) {
          var diff_msg = schema.difference(db_schema, false, true);
          if (diff_msg.length > 0) {
            goog.log.log(me.logger, goog.log.Level.FINER, diff_msg);
            setDb(null, new ydn.error.ConstraintError('different schema: ' +
                diff_msg));
          } else {
            setDb(db);
          }
        }
docs: Validate given schema and schema of opened database.
  @param {ydn.db.schema.Database} db_schema schema.