Entity Framework DBSet Extensions for type that implements an interface

Question

I am trying to create some DbSet<T> extensions where T implements INWatchStandardEntity .

Here is any example of one of them:

public static class NWatchDbSetExtensions
{
    public static Int32 GenerateId<TEntity>(this DbSet<INWatchStandardEntity> dbSet, string name) 
        where TEntity : INWatchStandardEntity, new()
    {
        NWatchObjectType objectType = Common.ToObjectType(dbSet.GetType());
        return Common.GetObjectIdFromName(objectType, name);
    }
}

This compiles fine, however, when I try to use the GenerateId(string name) on a DbSet that inherits from INWatchStandardEntity , for example:

using (var context = Application.GetDbContext()) {
    context.Nodes.GenerateId<INWatchStandardEntity>("name"); 
}

I get the following message:

' DbSet<Node> ' does not contain a definition for 'GenerateId' and the best extension method overload 'NWatchDbSetExtensions.GenerateId( DbSet<INWatchStandardEntity> , string )' requires a receiver of type ' DbSet<INWatchStandardEntity> '

Is there a way to make this and other extension methods available so that I can use it against any DbSet where Entity implements INWatchStandardEntity?

Answer 1

After some experimentation, here is the correct way of doing this:

public static Int32 GenerateId<TEntity>(this DbSet<TEntity> dbSet, string name) 
    where TEntity : class, INWatchStandardEntity
{
    NWatchObjectType objectType = Common.ToObjectType(dbSet.GetType());
    return Common.GetObjectIdFromName(objectType, name);
}