How to make generic function using LINQ?

Question

Based on information from here.

I found how deleting orphans with Entity Framework.

public void SaveChanges()
{
    context.ReportCards
        .Local
        .Where(r => r.Student == null)
        .ToList()
        .ForEach(r => context.ReportCards.Remove(r));

    context.SaveChanges();
}

I was wondering how to make generic function for this part because it might be used often:

context.ReportCards
        .Local
        .Where(r => r.Student == null)
        .ToList()
        .ForEach(r => context.ReportCards.Remove(r));

I thought about something like this:

public void SaveChanges()
{
   RemoveOrphans(Student, ReportCards) 
   context.SaveChanges();
}

private void RemoveOrphans<T>(T sourceContext, T orphan)
{    
    context.orphan
        .Local
        .Where(r => r.sourceContext == null)
        .ToList()
        .ForEach(r => context.orphan
        .Remove(r));
}

But of course it doesn't work. Any advice?

Answer 1

You can write extension method which does the same:

public static void RemoveOrphans<TEntity>(this IDbSet<TEntity> entities,
    Func<TEntity, bool> orphanPredicate)
    where TEntity: class
{
    entities.Local.Where(orphanPredicate).ToList().ForEach(e => entities.Remove(e));
}

And use it this way

context.ReportCards.RemoveOrphans(r => r.Student == null);
context.SaveChanges();

You can also use simple generic method which accepts IDbSet<TEntity> as first parameters, but it will not be such readable

RemoveOrphans(context.ReportCards, r => r.Student == null);
context.SaveChanges();