如何下面的SQL查询转换为LINQ查询在C＃

Question

select 
    t.Ticketid, t.subject, t.createdby, 
    count(TicketConversationId) as counts 
from 
    dbo.ticket t 
join 
    dbo.TicketConversation tc on t.ticketid = tc.ticketid 
group by 
    t.Ticketid, t.subject, t.createdby 

代码：

var Result = from t1 in Tickets 
      join t2 in TicketConversations on t1.TicketId equals t2.TicketId 
      select new { t1.TicketId, t1.Subject , comments = t2.TicketConversationId }; 

Answer 1

好所以要加计数和分组为您的查询使用GroupBy：

var result = from t1 in Tickets 
      join t2 in TicketConversations on t1.TicketId equals t2.TicketId 
      group t2.TicketConversationId by new { t.Ticketid, t.Subject, t.createdby } into g 
      select new { 
       t1.TicketId, 
       t1.Subject , 
       t1.CreatedBy, 
       Count = g.Count() }; 

请注意，在使用EF时，如果您正确定义了Navigation Properties，则不需要明确写入连接，而只需要t1.Conversations.Count()或类似。

---

因为所有你需要的是来计算记录在t2匹配，您可以使用group join

var result = from t1 in Tickets 
      join t2 in TicketConversations on t1.TicketId equals t2.TicketId into con 
      select new { 
       t1.TicketId, 
       t1.Subject, 
       t1.CreatedBy, 
       Count = con.Count() 
      };