将高级查询从SQL转换为LINQ

Question

仍然习惯LINQ语法，并且遇到了我需要在LINQ中创建的查询 - 但不完全确定如何。

SELECT *,
   (SELECT 1 FROM Applications 
   WHERE Applications.jID = Jobs.ID 
   AND Applications.uID = @uID) AS Applied 
FROM [Jobs]

在LinqPad中播放，但界面并没有真正帮助（至少我能看到的）。

Answer 1

根据Paul Sasik提供的链接以及他在LEFT OUTER JOIN之后的建议，此查询应符合您的要求;

var query = from job in jobs
            join app in applications on job.ID equals app.jID into grouped
            from subApp in grouped.DefaultIfEmpty()
            select new { Job = job, Applied = (subApp != null) };

修改： 要按用户过滤，请按以下步骤更新查询;

var query = from job in jobs
    join app in
    (
        from userApp in applications where userApp.uID == uID select userApp
    ) on job.ID equals app.jID into grouped
    from subApp in grouped.DefaultIfEmpty()
    select new { Job = job, Applied = (subApp != null) };

我个人原本会在此时直接使用.Where（）方法，但只是认为我会保持一致并继续使用查询语法。

Answer 2

var jobs = from j in this.db.Jobs
           where !j.Applications.Any(x => x.UserId == currentUserId)
           select j;

Answer 3

我建议您查看工具Linqer - 它将SQL转换为Linq代码。这不是免费的，但有10天的试用期。