batch.py 文件源码

def drop_constraint(self, const):
        if not const.name:
            raise ValueError("Constraint must have a name")
        try:
            const = self.named_constraints.pop(const.name)
        except KeyError:
            if _is_type_bound(const):
                # type-bound constraints are only included in the new
                # table via their type object in any case, so ignore the
                # drop_constraint() that comes here via the
                # Operations.implementation_for(alter_column)
                return
            raise ValueError("No such constraint: '%s'" % const.name)
        else:
            if isinstance(const, PrimaryKeyConstraint):
                for col in const.columns:
                    self.columns[col.name].primary_key = False