Question

I have a status field on a class that has an ID and a Name. I’m not using an enum to model it, but rather a class with some static values, like this:

    public class MailoutStatus : IEntity
{
    public static MailoutStatus Draft = new MailoutStatus() { Id = 1, Name = "Draft" };
    public static MailoutStatus Scheduled = new MailoutStatus() { Id = 2, Name = "Scheduled" };
    public static MailoutStatus Cancelled = new MailoutStatus() { Id = 3, Name = "Cancelled" };
    public static MailoutStatus Sent = new MailoutStatus() { Id = 4, Name = "Sent" };

    public int Id { get; set; }
    public string Name { get; set; }
...
}

Now I want to set this status value on the object it describes, like so:

        var repo = new MailoutRepository();
        var mailout = repo.Get(1);
        mailout.Status = MailoutStatus.Cancelled;
        repo.Update(mailout);
        repo.CommitChanges();

However, this code will see MailoutStatus.Cancelled as a new entity and will insert a new row into the MailoutStatus table, ignoring the ID that is already on Cancelled and adding a new IDENTITY generated ID (for instance, 5). I can prevent this by adding an entityvalidation stuff, but that just makes the above blow up due to the validation failure.

I can work around the issue using this code:

    var repo = new MailoutRepository();
    var mailout = repo.Get(1);
    mailout.Status = new MailoutStatusRepository().Get(MailoutStatus.Cancelled.Id);
    repo.Update(mailout);
    repo.CommitChanges();

This works because now Entity Framework knows about the MailoutStatus that I’m fetching and is tracking its state, etc. But it’s really crappy to have to write that much code just to set a status. I also don’t want to use an enum for other reasons and I don’t want MailoutStatus to know anything about persistence. Any ideas?

Answer 1

Here’s how I solved it.

I defined an attribute named NotTrackedAttribute and apply that on entities like Status. Then override the SaveChanges method of the derived context as follows. Reset the tracked changes to those entities

    public override int SaveChanges()
    {
        var changedEntities = ChangeTracker.Entries();

        foreach (var changedEntity in changedEntities)
        {
             var entity = changedEntity.Entity;

             //ignore the types that are marked as NotTracked
             if (Attribute.IsDefined(entity.GetType(), typeof(NotTrackedAttribute)))
             {
                 changedEntity.State = EntityState.Unchanged;
                 continue;
             }
        }

        return base.SaveChanges();
    }

The attribute

/// <summary>
/// Indicates that a Type having this attribute should not be persisted.
/// </summary>
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
public class NotTrackedAttribute : Attribute
{
}

Then use it as follows

[NotTracked]
public class MailoutStatus
{

}