linq to sql的不同值或分組依據

Question

我有以下linq查詢。
如何修改查詢以僅返回CityFoo屬性的不同值？

var query = from f in db.Foos
             join b in db.Bars on f.IDFoo equals b.IDFoo
             join fb in db.Fubars on b.IDBar equals fb.IDBar
             select new MyViewModel {
                    IDFoo = f.IDFoo,
                    NameFoo = f.NameFoo,
                    CityFoo = f.CityFoo,
                    NameBar = b.NameBar,
                    NameFubar = fb.NameFubar };

Answer 1

我認為您缺少查詢信息。 如果要在其他屬性上使用第一個值，則需要告知Linq

所以我猜您實際上是想分組然后再拿第一。

或者...這樣的事情：

var query = from f in db.Foos
             join b in db.Bars on f.IDFoo equals b.IDFoo
             join fb in db.Fubars on b.IDBar equals fb.IDBar
             group  new { f, b, fb } by f.CityFoo into grp
             let first = grp.FirstOrDefault()
             select new MyViewModel {
                    IDFoo = first.f.IDFoo,
                    NameFoo = first.f.NameFoo,
                    CityFoo = grp.Key,
                    NameBar = first.b.NameBar,
                    NameFubar = first.fb.NameFubar };