Question

I have a pretty simple problem with a not-so-obvious solution. I have a relational mapping in my database between Users and Roles, and each user can be mapped to one or more roles. So the mapping is like so:

User < 1:n > UserRole < n:1 > Role

In my generated EF4 POCOs, User and Role each have an ICollection of the other:

public class User 
{
    //Bunch of other properties/methods

    public virtual ICollection<Role> Roles
}

public class Role
{
    //Bunch of other properties/methods

    public virtual ICollection<User> Users
}

Now, I’ve implemented the IoC, UoW, and repository patterns illustrated in this article, which uses an ObjectSet to fetch/persist the data via repositories.

My question is, how do I implement this:

public bool UserIsInRole(int userId, int roleId)

I have tried the following:

public bool UserIsInRole(int userId, int roleId)
{
    Role role = _roleRepository.Single(r => r.Id == roleId);
    return _userRepository.SingleOrDefault(u => u.Roles.Contains(role)) != null;
}

But it fails with:

Unable to create a constant value of type ‘Data.Models.Role’. Only primitive types (‘such as Int32, String, and Guid’) are supported in this context.

Plus, it’s not a very elegant implementation as it’s having to hit the database twice.

I was looking for something like this:

return _userRepository.SingleOrDefault(u => u.Roles.Where(r => r.Id = roleId));

But ICollection doesn’t support LINQ.

How can I do this, and ideally, how can I do it with one LINQ expression and one trip to the database?

Or, am I going about this completely wrong?

Thanks in advance.

Solved:
Thanks to all who posted. All gave an acceptable answer. I accepted the one that was the most elegant.

Answer 1

There is a more concise way to do it:

public bool UserIsInRole(int userId, int roleId)
{
    return _userRepository.
            Any(u => u.Id == userId && 
                     u.Roles.Any(r => r.Id == roleId));
}