Question

I’m working on a reusable database repository method for attaching and saving entities to a database using EntityFramework 4.3.

    private void SaveObject<T>(T entityToSave, DbSet<T> dbSet) where T : class
    {
        if (db.Entry(entityToSave).State == EntityState.Detached)
        {
            if (entityToSave.Id == Guid.Empty) // how do I access the Id property?
                dbSet.Add(entityToSave);
            else
                db.Entry(entityToSave).State = EntityState.Modified;
        }
    } 

The problem that I’m running into is that I need to tell my method which property is the Id so I can check to see if it is set or not. If it is empty, then I know I am creating a brand new record. Otherwise I am modifying an existing record.

How do I tell my method what the Id property is?

Answer 1

You need an interface or base class that defines the Id property, and use that as your generic constraint. Example:

public interface IEntity
{
    Guid Id { get; }
}

private void SaveObject<T>(T entityToSave, DbSet<T> dbSet) where T : class, IEntity
    {
        if (db.Entry(entityToSave).State == EntityState.Detached)
        {
            if (entityToSave.Id == Guid.Empty) // how do I access the Id property?
                dbSet.Add(entityToSave);
            else
                db.Entry(entityToSave).State = EntityState.Modified;
        }
    }