Linq - 帶點符號的左外連接

Question

如何使用點符號在linq中執行左外連接？

這裏的查詢表達式：

var query = from u in db.Users 
      join d in db.Defects on u.userID equals d.userID into defectsGroup 
      from d in defectsGroup.DefaultIfEmpty() 
      select new { u, d }; 

這裏是我的嘗試：

var query2 = db.Users.GroupJoin(db.Defects.DefaultIfEmpty(), 
       u => u.userID, 
       d => d.userID, 
       (user, defect) => new { user, defect }); 

但缺陷是顯示爲IEnumerable<Defect>而不僅僅是Defect。我也試過：

var query2 = db.Users.GroupJoin(db.Defects, 
       u => u.userID, 
       d => d.userID, 
       (user, defect) => new { user, defect.DefaultIfEmpty() }); 

哪個根本不會編譯。所有在線示例似乎都使用（更清晰）查詢語法。

Answer 1

我想你想要這樣的：

var query2 = db.Users.GroupJoin(db.Defects, 
           u => u.userId, 
           d => d.userID, 
           (u, defectsGroup) => new { u, defectsGroup}) 
        .SelectMany(z => z.defectsGroup.DefaultIfEmpty(), 
           (z, d) => new { z.u, d }); 

見我Edulinq blog post on query expressions瞭解更多詳情。