实体框架多个计数与一个查询 [英] Entity Framework multiple counts with a single query

问题描述

对不起，如果这是被问到，但是如何通过单次调用数据库来改善以下内容？

Sorry if this has been asked, but how can I improve the following with a single call to the database?

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

推荐答案

首先您可以计算被拒绝按总计和接受如下：

First of all you can compute the Rejected by Total and Accepted like this:

Rejected = Total - Approved

为进一步改进，您可以一次计算两者;

And for further improvement you can compute both of them in one shot;

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：
a现在简单的黑客：只需拿第一行

UPDATE: a simple hack for now : just take the first row

(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一个

But I'm looking for a cleaner one

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