public class FooService : IFooService
{
    private DomainContext db;

    public FooService(DomainContext db)
    {
        this.db = db;
    }

    public void MergeEntities(Entity source, Entity target)
    {
        using (var uow = db.Database.BeginTransaction())
        {
            // merge source into target

            db.SaveChanges();

            uow.Commit();
        }
    }
}

public class FooService : IFooService
{
    private DomainContext db;

    public FooService(DomainContext db)
    {
        this.db = db;
    }

    public void MergeEntities(Entity source, Entity target)
    {
        // merge source into target

        db.SaveChanges();
    }
}