Question

I have a UserClasses, Screens and Workflow tables. The Workflow table is the association table between the UserClasses and Screens tables. Here are their structures…

UserClasses
- UserClassID (int PK)
- UserClass (string)

Screens
- ScreenID (int PK)
- ScreenName (string)

Workflow
- UserClassificationID
- ScreenID

I have the following data in the UserClasses table (Id and name):

- 1 UserClassification1
- 2 UserClassification2
- 3 UserClassification3
- 4 UserClassification4
- 5 UserClassification5

I have the following data in the Screens table (Id and name):

- 1 Screen1
- 2 Screen2
- 3 Screen3

I have the following data in the Workflow table (UserClassificationID and ScreenID):

1 1
1 2

By looking at the data Screen3 is not associated to a user classification. This is what I need, a list of all the screens that are not associated to a given user classification. How would I do this?

Additional information regarding my setup. The 2 classes that I have defined for the UserClasses and Screens tables:

public class UserClassification : IEntity
{
     public int Id { get; set; }
     public string Name { get; set; }
     public virtual ICollection<Screen> Screens { get; set; }
}

public class Screen : IEntity
{
     public int Id { get; set; }
     public string Name { get; set; }
     public virtual ICollection<UserClassification> UserClassifications { get; set; }
}

Here are the configurations classes that is used in my database context class:

class ScreenConfiguration : EntityTypeConfiguration<Screen>]
{
     internal ScreenConfiguration()
     {
          this.Property(x => x.Id).HasColumnName("ScreenID");
          this.Property(x => x.Name).HasColumnName("ScreenName");
     }
}

class UserClassificationConfiguration : EntityTypeConfiguration<UserClassification>
{
     internal UserClassificationConfiguration()
     {
          this.ToTable("UserClasses");
          this.Property(x => x.Id).HasColumnName("UserClassID");
          this.Property(x => x.Name).HasColumnName("UserClass");
          this.HasMany(i => i.Screens)
               .WithMany(c => c.UserClassifications)
               .Map(mc =>
               {
                    mc.MapLeftKey("UserClassificationID");
                    mc.MapRightKey("ScreenID");
                    mc.ToTable("Workflow");
               });
     }
}

So given the above information I need to return a user classification object with a list of screens that are not associated to this user classification, in this case that would be a list of 1 screen item. How would I do something like this?

This is how I return a user classification object with a list of screens that are in the association table:

return DbContext.UserClasses
     .Include("Screens")
     .SingleOrDefault(x => x.Id == userClassificationId);

Answer 1

What about ?

from s in DbContext.Screens
where s.UserClassifications.Count() == 0
select s

hope this helps