将linq转换为具有多个连接的lambda

Question

我正在尝试将此linq查询转换为lambda

 var query = (from a in context.Table_A
                         join u in context.Table_B  on a.scored equals u.userid
                         join u2 in context.Table_B on a.scorer equals u2.userid
                         from cs in a.Table_C //(Table_A is related to Table_C)
                         where (a.date>= startdate && a.date < enddate)
                         select new MSViewModel
                         {
                             scored= u.User.name,
                             scorer= u2.User.name,
                             subject_name = cs.Subject.name,
                             score = cs.score,
                             categoryid = cs.id,
                         })
                            .AsEnumerable()
                            .GroupBy(t => t.scored)
                            .ToList();

到目前为止，这就是我所拥有的。我有点失去下一步该做什么。

 var tobi = db.Table_A.Join(db.Table_B,a=>a.scored,u=>u.userid,
                    (a,u) => new {scored=u.User.name });
                    db.Table_A.Join(db.Table_B,a1=>a1.scorer,u2=>u2.userid, 
                    (a,u2)=> new {scorer= u2.User.name});

Answer 1

首先，我同意Arran的评论：查询表达式将更容易处理。我绝对认为使用lambda表单是有意义的，但是在查询表达式中，连接通常很多更简单。

话虽如此，你基本上需要模仿transparent identifiers。下面的代码未经测试，但对我来说看起来很模糊。

var query = context.Table_A
                   .Join(context.Table_B, a => a.scored, u => u.userid,
                         (a, u) => new { a, u })
                   .Join(context.Table_B, p => p.a.scorer, u2 => u2.userid,
                         (p, u2) => new { p, u2 })
                   .SelectMany(q => q.p.a.TableC, (q, cs) => new { q, cs })
                   .Where(r => r.q.p.a.date >= startdate && r.q.p.a.date < enddate)
                   .Select(q => new MSViewModel {
                                  scored= r.q.p.u.User.name,
                                  scorer= r.q.u2.User.name,
                                  subject_name = r.cs.Subject.name,
                                  score = r.cs.score,
                                  categoryid = r.cs.id,
                                })
                   .AsEnumerable()
                   .GroupBy(t => t.scored)
                   .ToList();

基本上p和q以及r是透明标识符。你有三个，因为你有两个连接和一个后续的from子句。

Answer 2

要扩展我的评论，如果你有Resharper：

Resharper显示将LINQ转换为Lambada 的选项

转化后：

Answer 3

试试这个：

    var query = (_context.Table_A.Join(_context.Table_B, a => a.scored, u =>
    u.userid,
    (a, u) => new {a, u}).Join(_context.Table_B,
    @t => @t.a.scorer,
    u2 => u2.userid,
    (@t, u2) => new {@t, u2}).
    SelectMany(@t => _context.Table_A, (@t, cs) => new MSViewModel()
    {
    scored = @t.@t.u.User.name,
    scorer= @t.u2.User.name,
    subject_name = @t.cs.Subject.name,
    score = @t.cs.score,
    categoryid = @t.cs.id,
    })).AsEnumerable()
    .ToList();