operations.py 文件源码

def post_migrate_mpathnode(model):
    # Note: model *isn't* a subclass of MPathNode, because django migrations are Weird.
    # if not issubclass(model, MPathNode):
    # Hence the following workaround:
    try:
        ltree_field = model._meta.get_field('ltree')
        if not isinstance(ltree_field, LTreeField):
            return
    except FieldDoesNotExist:
        return

    names = {
        "table": quote_ident(model._meta.db_table, connection.connection),
        "check_constraint": quote_ident('%s__check_ltree' % model._meta.db_table, connection.connection),
    }

    cur = connection.cursor()
    # Check that the ltree is always consistent with being a child of _parent
    cur.execute('''
        ALTER TABLE %(table)s ADD CONSTRAINT %(check_constraint)s CHECK (
            (parent_id IS NOT NULL AND ltree ~ (parent_id::text || '.*{1}')::lquery)
            OR (parent_id IS NULL AND ltree ~ '*{1}'::lquery)
        )
    ''' % names)