Question

I have following two entities

public class User
{
   public int UserId { get; set; }
   public string UserName { get; set; }
   public List<Department> Departments { get; set; }
}

public class Department
{
   public int DepartmentId { get; set; }
   public string DepartmentName { get; set; }
   public List<User> Users { get; set; }
}

As you see, relationship between two objects is M:N.
I wanna get User who only have specific department ID, in this case, How to get users using Linq?

Thanks in advance

Answer 1

int requiredId = ...   
var usersInReqdDept = Users.Where(u => u.Departments
                                        .Any(d => d.DepartmentId == requiredId));

If the Departments list can be null, you will need a null-check in the Where clause.

If you want to search the Departments list instead,

int requiredId = ...   
var usersInReqdDept = Departments.Single(d => d.DepartmentId == requiredId)
                                 .Users;

Of course, this will throw an exception if such a department doesn’t exist.