左连接和与列在LINQ区分

我有两个关系：Users和UserProjects。左连接和与列在LINQ区分

我想检查哪个用户已经在项目中。到目前为止，它是这样的：

var usrs = (from users in context.Users 
         join userProj in context.UserProjects 
         on users.UserId equals userProj.UserId into gj 
         from subuserProject in gj.DefaultIfEmpty() 
         select new ProjectUsersDTO 
         { 
          UserName = users.Name, 
          Rate = users.RatePerHour, 
          UserId = users.UserId, 
          alreadyInProject = subuserProject == null || subuserProject.ProjectId != projectId ? false : true 
         }) 
         .ToList();

问题是我想让他们不同。现在我得到一个用户alreadyInProject == true和alreadyInProject == false。

来源

2016-02-12 miechooy

这是完全一样的你的[上一个问题]（http://stackoverflow.com/questions/35296388/linq-union-vs-sql-union），我已经给你[答]（http：// stackoverflow .COM /问题/ 35296388/LINQ工会-VS-SQL工会/ 35297463＃35297463） –

如果你正在检查一些特定的项目，那么你就不需要参加所有项目 - 加盟之前，只过滤用户项目：

from user in context.Users 
join userProj in context.UserProjects.Where(up => up.ProjectId == projectId) 
    on user.UserId equals userProj.UserId into g 
from subuserProject in g.DefaultIfEmpty() 
select new ProjectUsersDTO { 
    UserName = user.Name, 
    Rate = user.RatePerHour, 
    UserId = user.UserId, 
    alreadyInProject = (subuserProject != null) 
}

生成的查询将看起来像

SELECT 
    [Extent1].[UserId] AS [UserId], 
    [Extent1].[Name] AS [Name], 
    [Extent1].[RatePerHour] AS [RatePerHour], 
    CASE WHEN ([Extent2].[UserProjectId] IS NOT NULL) 
     THEN cast(1 as bit) 
     ELSE cast(0 as bit) 
    END AS [C1] 
    FROM [dbo].[Users] AS [Extent1] 
    LEFT OUTER JOIN [dbo].[UserProjects] AS [Extent2] 
    ON ([Extent2].[ProjectId] = @p__linq__0) AND ([Extent1].[UserId] = [Extent2].[UserId])

来源

2016-02-12 11:40:46

左连接和与列在LINQ区分

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