Question

我有这样的Linq查询：

var items = from v in work.GetRepo<VW_V>().Query
        join k in work.GetRepo<K>().Query on v.Loc_Id equals k.Id
        join p in work.GetRepo<P>().Query on v.Peer_Id equals p.Id
        join tt in work.GetRepo<TT>().Query on v.Item_Id equals tt.Id
        select (new MyModel
        {
            Id = v.Id,
            Location = k != null ? k.Name : string.Empty,
            ItemName = tt.Name,
            Peer = p != null ? p.Name : string.Empty,
        });

此查询正常。但我希望有记录表明他们中的一些人没有同伴。我怎样才能做到这一点？此查询返回仅具有Peers的记录，如何拥有具有peer且不具有peer的记录。如果该记录中存在peer，我想显示Peer的名字。感谢。

Answer 1

它被称为左outer join。尝试：

var items = from v in work.GetRepo<VW_V>().Query
        join k in work.GetRepo<K>().Query on v.Loc_Id equals k.Id
        join p in work.GetRepo<P>().Query on v.Peer_Id equals p.Id into subpeer_j
        from subpeer in subpeer_j.DefaultIfEmpty()
        join tt in work.GetRepo<TT>().Query on v.Item_Id equals tt.Id
        select (new MyModel
        {
            Id = v.Id,
            Location = k != null ? k.Name : string.Empty,
            ItemName = tt.Name,
            Peer = subpeer != null ? subpeer.Name : string.Empty,
        });

Answer 2

var items = from v in work.GetRepo<VW_V>().Query

            join k in work.GetRepo<K>().Query 
              on v.Loc_Id equals k.Id

            join p in work.GetRepo<P>().Query 
              on v.Peer_Id equals p.Id
            into pJoinData 
            from pJoinRecord in pJoinData.DefaultIfEmpty( )

            join tt in work.GetRepo<TT>().Query 
              on v.Item_Id equals tt.Id

            select (new MyModel
            {
                Id = v.Id,
                Location = k != null ? k.Name : string.Empty,
                ItemName = tt.Name,
                Peer = pJoinRecord != null ? pJoinRecord.Name : string.Empty,
            });

Linq连接接受空值

2 个答案: