c# - Entity Framework 使用单个查询进行多次计数

Question

抱歉，如果有人问过这个问题，但是我如何通过一次调用数据库来改进以下内容？

var statsModel = new
{
     Total = _db.Messages.Count(),
     Approved = _db.Messages.Count(x => x.Approved),
     Rejected = _db.Messages.Count(x => !x.Approved),
};

Answer 1

首先你可以计算Rejected通过总计和接受这样的:

Rejected = Total - Approved

为了进一步改进，您可以一次性计算它们；

from m in _db.Messages
let Total =  _db.Messages.Count()
let Accept = _db.Messages.Count(x => x.Approved == true)
select new {Total , Accept})

更新:
现在一个简单的黑客:只需要第一行

(from m in _db.Messages
let Total =  _db.Messages.Count()
let Accept = _db.Messages.Count(x => x.Approved == true)
select new {Total , Accept}).Take(1);

但我正在寻找一个更干净的