ORM 怎么跨库连表操作?

protected function _blogQueryBuilder($where=[],$fields=[])
    {
        // whereIn 条件
        $whereIn        =   array_filter($where['in'] ?? []);
        // where条件
        $where          =   array_filter(array_merge( $where['where'] ?? [[]], [ ['b.status',1] ] ));
        $builder =  Blog::from('blog as b')->select(...$this->allowFields)
            ->leftjoin('blog_category_relation as r','b.uuid','=','r.buuid')
            ->leftjoin('manage.manage_admin as a','a.uuid','=','b.createdby');
        $where && $builder->where( $where );
        $whereIn && $builder->whereIn( ...$whereIn );
        return $builder;
    }

请问‘manage.manage_admin’这段跨库应该怎么表述?