多对多关系的扩展方法语法

Question

Bit of Linq method syntax from a newbie here, so I appreciate any insights anyone can pass along. What I need seems simple, but it's running me around in circles. I have 2 tables and an association (basically a junction table with only 2 fields). I've gone through numerous posts on SO, but I'm just not getting it. Frustrating. Ok, using EF4, I have Reports and Roles and a navigation property on Reports called Roles which is the junction table (with ReportId and RoleId fields, both integer fields). I use a UserId to get all associated roles from the Roles table, use those roles to get the associated reports from the junction table and then get the names of the reports from Reports.

I've tried LinqPad, but what it produces in lambda method syntax won't even work when I paste it back into LinqPad.

SQL query:

select Reports.ReportName 
 from Reports 
 inner join UserRoles on Reports.ReportId = UserRoles.ReportId 
 inner join Roles on Roles.RoleId = UserRoles.RoleId 
 where UserRoles.UserId == userId

Code so far:

Reports.Select(a => a.Roles.Where(t => t.UserRoles.Select(u => u.UserId == userId)));

Answer 1

You can give this a shot, you may also want to filter down your select based on your needs:

var result = from allReports in Reports
             join userRoles in userRoles on allReports.ReportId equals userRoles.ReportId
             join roles in Roles on userRoles.RoleId equals roles.RoleId
             where userRoles.UserId == userid
             select allReports; 

Answer 2

I think this query syntax is much better in this case:

var query = from report in db.Reports
            join ur in db.UserRoles on report.ReportId equals ur.ReportId
            join role in db.Roles on ur.RoleId equals role.RoleId
            where ur.UserId == userId
            select report.ReportName;