Question

我正在尝试使用以下语句对某些数据库数据进行分组。

var res = from messages in db.Messages
group messages by messages.Message_Sent_Date into grp
select new { message_count = grp.Sum(g => g.Message_Count), message_cost = grp.Sum(g => g.Customer_Price) };

相当于：

var query = db.Messages.Where(m => m.Message_Sent_Date != null && m.Message_Count != 99)
                       .GroupBy(d => d.Message_Sent_Date)
                       .Select(g => new {
                               message_count = g.Sum(c => c.Message_Count),
                               message_cost = g.Sum(c => c.Customer_Price),
                           });

我的问题是，所选对象有2个字段，即message_count和message_cost。如果我想添加第三个字段'Message_Sent_Date'，它实际上是数据分组的列。我该怎么做？

Answer 1

使用g.Key作为每个组的Message_Sent_Date，因此代码段将如下所示：

 // Modified select after the GroupBy clause 
.Select(g =>
        new
        {
            message_count = g.Sum(c => c.Message_Count),
            message_cost = g.Sum(c => c.Customer_Price),
            Message_Sent_Date= g.Key
        });

然后，Groupby使用lambda / linq选择数据

1 个答案: