SQL to LINQ 涉及多个 GroupJoin

Question

我有一个 SQL 查询并想转换为 LINQ 方法语法 (Lambda)，但我似乎被困在多组连接中，这让我很困惑。 下面是我想改成LINQ的SQL

select MerchantUserId, usex.Nickname, MAX(OrderTransaction.CreatedDate) as LastOrderDate, sd.Url, st.Name as storename
from OrderTransaction
    left join UserExtend usex
    on usex.Id = OrderTransaction.MerchantUserId
    left join StoreDomain sd 
    on sd.StoreId = usex.StoreId
    left join store st
    on st.id = sd.StoreId
where OrderTransaction.Status <> 8
    and sd.IsPrimary = 1    
group by MerchantUserId,usex.Nickname,sd.Url,st.Name
order by LastOrderDate desc

下面是我尝试将所有三个表链接在一起的查询。在将 3 个表格链接在一起方面，我做得对吗？

    var list = _ApplicationDbContext.UserExtend
.GroupJoin(_ApplicationDbContext.OrderTransaction, usex => usex.Id, ord => ord.MerchantUserId, (usex, ord) => new { usex, ord})
.GroupJoin(_ApplicationDbContext.StoreDomain, usexOrd => usexOrd.usex.StoreId, sd => sd.StoreId, (usexOrdStoreDom, sd) => new { usexOrdStoreDom , sd})
.GroupJoin(_ApplicationDbContext.Store, usexOrdStoreDom => usexOrdStoreDom.usexOrdStoreDom.usex.StoreId, st => st.Id, (usexOrdStoreDomStore , st ) => new { usexOrdStoreDomStore, st })

Answer 1

与您的 SQL 查询等效的是以下链接短语。 GroupJoin 用于将一个值与多个值匹配时使用。

更多信息可以参考这个链接：Linq to Entities join vs groupjoin

var list = _ApplicationDbContext.UserExtend.Join(_ApplicationDbContext.OrderTransaction,
      usex => usex.Id,
      ord => ord.MerchantUserId,
      (usex, ord) => new { usex, ord })
      .Join(_ApplicationDbContext.StoreDomain,
      usexOrd => usexOrd.usex.StoreId,
      sd => sd.StoreId,
      (usexOrd, sd) => new { usexOrd, sd })
      .Join(_ApplicationDbContext.Store,
      usexOrdStoreDom => usexOrdStoreDom.sd.StoreId,
      st => st.Id,
      (usexOrdStoreDom, st) => new { usexOrdStoreDom, st })
      .GroupBy(a => new { a.usexOrdStoreDom.usexOrd.ord.MerchantUserId, a.usexOrdStoreDom.usexOrd.usex.Nickname, a.usexOrdStoreDom.sd.Url, a.st.Name, a.usexOrdStoreDom.usexOrd.ord.CreatedDate })
      .OrderBy(a => a.Key.CreatedDate)
      .Select(a => new
      {
         MerchantUserId = a.Key.MerchantUserId,
         Nickname = a.Key.Nickname,
         Url = a.Key.Url,
         storename = a.Key.Name,
         LastOrderDate = a.Max(x => x.usexOrdStoreDom.usexOrd.ord.CreatedDate)
      })
      .ToList();