c# - Linq - 带点符号的左外连接

Question

我如何使用点符号在 linq 中进行左外连接？

这是查询表达式:

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 };

这是我尝试过的:

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

但缺陷显示为 IEnumerable<Defect>而不仅仅是 Defect .我也试过:

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

根本无法编译。所有在线示例似乎都使用(更清晰的)查询语法。

Answer 1

我想你想要这个:

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 });

查看我的 Edulinq blog post on query expressions了解更多详情。