Question

很抱歉，如果有人问这个问题，但是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

这可能会有所帮助：

var statsModel =(
        from message in _db.Messages
        group message by 1 into g
        select new
        {
            Total = g.Count(),
            Approved =g.Count (x =>x.Approved),
            Rejected =g.Count (x =>!x.Approved)
        }
    ).FirstOrDefault();

Answer 2

首先，您可以按照总计和接受度计算Rejected：

Rejected = Total - Approved

为了进一步改进，你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})

<强>更新现在简单的黑客攻击：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清洁的人

Answer 3

在C＃中（而不是LINQ查询中），异步语法：

var statsModel = await _db.Messages
.GroupBy(m => 1, (g, mm) => new
{
    Total = mm.Count(),
    Approved = mm.Count(m => m.Approved),
    Rejected = mm.Count(m => !m.Approved)
})
.SingleAsync();

实体框架多次使用单个查询计数

3 个答案: