Question

I have two methods and don’t like the duplication:

public Order LatestOrderOver(decimal amount)
{
    return session.QueryOver<Order>()
        .Where(o => o.Amount > amount)
        .OrderBy(sr => sr.CompleteUtcTime).Desc
        .Take(1)
        .SingleOrDefault<Order>();
}

public Order LatestAmericanOrderOver(decimal amount)
{
    return session.QueryOver<Order>()
        .Where(o => o.Amount > amount && o.Country == "USA")
        .OrderBy(sr => sr.CompleteUtcTime).Desc
        .Take(1)
        .SingleOrDefault<Order>();
}

What is the best way to avoid duplication when you have similar criteria (in the Where clause) used in the QueryOver and similar options at the end?

Answer 1

If you are using Linq To Objects, you can just refactor out the delegate:

private Order LatestOrderOver(Func<Order, bool> f) {
  return
    session.QueryOver<Order>()
    .Where(f)
    .OrderBy(sr => sr.CompleteUtcTime).Desc
    .Take(1)
    .SingleOrDefault<Order>();
}

public Order LatestOrderOver(decimal amount) {
  return LatestOrderOver(o => o.Amount > amount);
}

public Order LatestAmericanOrderOver(decimal amount) {
  return LatestOrderOver(o => o.Amount > amount && o.Country == "USA");
}

Otherwise it might work with just changing Func<> to Expression<>, but I don’t have much experience with that.