如何在EF ASP.NET MVC5中的lambda表达式中创建简单的左外部联接 [英] How to create a simple left outer join in lambda expression in EF ASP.NET MVC5

问题描述

我搜索了几个小时，没有任何运气.我正在尝试创建一个lambda表达式，以从两个表Schedule和Request中获取数据.但是我在这里输出一个布尔值.我如何做一个合适的左外连接来解决这个问题? 这是我能想到的最好的

I searched hours and hours for this without any luck. I'm trying to create a lambda expression to fetch data from two tables Schedule and Request. But i'm outputting a bool here. How can i do a proper left outer join to fix this? this is the best i could come up with

ViewBag.RequestList = db.Requests
    .Include(r => r.Department)
    .Select(r => db.Schedules.Any(s => s.RequestId == r.RequestId));

但不是列表.

假设我的表格模型如下

public class Request{
 public virtual int RequestId { get; set; }
 public virtual string Remarks { get; set; }
}

public class Schedule{
 public virtual int ScheduleId{ get; set; }
 public virtual string Name{ get; set; }
 public virtual Request Request { get; set; }
}

我正在尝试查看每个请求是否都具有一个或多个与之关联的时间表.因此，如果我可以将日程表对象附加到请求并将其输出为列表，那么多数民众赞成在我所需要的. 但是我想使用LINQ和lambda表达式来做到这一点，而且我看到了如下查询；

I'm trying to see if each and every request has one or more schedules associated with it or not. so if i could attach schedule object to request and output it as a list then thats all i need. But I want to do it using LINQ and lambda expressions and I've seen queries as below;

var leftList = (from emp in db.Requests
                join d in db.Schedules
                on emp.RequestId equals d.RequestId into output
                from j in output.DefaultIfEmpty()
                select new { RequestId = emp.RequestId, 
                             name = emp.Department.Name, 
                             route = emp.Route.Name });

但这不是我想要的，因为我必须在new { RequestId = emp.RequestId, name = emp.Department.Name, route = emp.Route.Name }

But that's not what i want, because i have to specify every field i need in new { RequestId = emp.RequestId, name = emp.Department.Name, route = emp.Route.Name }

非常感谢！

推荐答案

只列出您想要的内容:

          var leftList =    from emp in db.Requests
                            join d in db.Schedules
                            on emp.RequestId equals d.RequestId into output
                            from j in output.DefaultIfEmpty()
                            select new 
                            { 
                               RequestId = emp.RequestId,
                               name = emp.Department.Name, 
                               route = emp.Route.Name,
                               ScheduleId=j==null?0:j.ScheduleId,
                               SName=j==null?""j.Name,
                            };

这篇关于如何在EF ASP.NET MVC5中的lambda表达式中创建简单的左外部联接的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！