LINQ 按表达式语法分组

Question

我有一个类似这样的 T-SQL 查询：

SELECT r_id, r_name, count(*)
FROM RoomBindings
GROUP BY r_id, r_name

我想用 LINQ 做同样的事情。到目前为止，我到了这里：

var rooms = from roomBinding in DALManager.Context.RoomBindings
                        group roomBinding by roomBinding.R_ID into g
                        select new { ID = g.Key };

如何提取 count(*) 和 r_name 部分？

Answer 1

试试这个：

var rooms = from roomBinding in DALManager.Context.RoomBindings
                        group roomBinding by new 
                        { 
                           Id = roomBinding.R_ID, 
                           Name = roomBinding.r_name
                        }
                        into g
                        select new 
                        { 
                           Id = g.Key.Id,
                           Name = g.Key.Name,
                           Count = g.Count()  
                        };

由 Nick 编辑 - 添加了用于比较的方法链语法

var rooms = roomBinding.GroupBy(g => new { Id = g.R_ID, Name = g.r_name })
                       .Select(g => new
                           {
                               Id = g.Key.Id,
                               Name = g.Key.Name,
                               Count = g.Count()
                           });