实体框架通过ID删除N：M关系

Question

I have a Simple table like this:

User(Id, FirstName, ...) <===> Role(Id, Title, ...)

witch have N:M relation

what i want to do is to remove the relation in between them by having there Ids, so my method should be like this :

public void UnlinkUsersFromRoles(int[] roleIds, int[] userIds)
{
    var myContext = new DefaultContext();
    // ?? <= how to break the relation without loading unnecessary columns
}

Answer 1

Can you just do this:

var rolesToRemove = myContext.Roles.Where(r=> roleIds.Contains(r.Id)).ToArray();
foreach(var user in myContext.Users.Where(u=> userIds.Contains(u.Id)){
   forearch(var var role in rolesToRemove) {
       user.Roles.Remove(role);
   } 
}
myContext.SaveChanges();

When you say:

how to break the relation without loading unnecessary columns

You mean, the above code doesn't fullfill you requeriment?

EDIT:

If you have a explicity relationship class like UserInRoles, you should use John Castleman Answer, or just create one, map the ForeignKeys and use his solution.

Answer 2

If this is many-to-many relationship, there must be a join table in between: for these tables User and Role , let's say it's called UserRole , and is a simple join table (ie, no other columns on that table, other than the FK ids to the other two tables):

public class UserRole
{
    public int UserId { get; set; }
    public int RoleId { get; set; }
}

With an explicitly defined join table such as this, UnlinkUsersFromRoles could be defined as follows:

public void UnlinkUsersFromRoles(int[] roleIds, int[] userIds)
{
    using (var context = new DefaultContext())
    {
        foreach (var ur in context.UserRoles
                                  .Where(u => userIds.Contains(u.UserId))
                                  .Where(r => roleIds.Contains(r.RoleId))
                                  .ToArray())
        {
            context.UserRoles.Remove(ur);
        }

        context.SaveChanges();
    }
}

You're certainly going to wind up loading all the UserRole rows to be removed in when you call ToArray , but this is certainly better than loading in all the related User and Role rows.