c# - 林奇 : Error using multiple from and Join

Question

以下 LINQ:

var result = from u in db.userdetails
    from b in db.bids
    join x in db.Others on b.UserId equals x.UserId into others
    from o in others.DefaultIfEmpty()
    from p in db.Products
    where u.UserID.Equals(b.UserId)
    && p.BidId.Equals(b.BidId)
    && b.DocId == id

给我错误:

The type of one of the expressions in the join clause is incorrect. Type inference failed in the call to 'GroupJoin'.

Answer 1

通过重新组织您的 join 和 where 子句，您可能会有更好的运气(和更易于维护的代码)。使用 LINQ 实现，您不必总是在所有 from 子句之后都有 where 子句:

var result = 
    from u in db.userdetails 
    join b in db.bids on u.UserID equals b.UserId
         where b.DocID == id
    join p in db.Products
         on b.BidID equals p.BidId
    join x in db.Others on b.UserId equals x.UserId into others 
    from o in others.DefaultIfEmpty() 
    Select ???

话又说回来，如果您的实体之间有适当的关联，您可能能够避免所有连接，并通过直接导航对象图来投影到所需的形状。