Question

I have written the following linq statement but I can’t help feeling it could be simplified somehow. The purpose is to take a List<IEnumberable<Counterparty>> (counterpartyStatic in the query) objects and find the Orders that have a ClientId equal to Counterparty.CounterpartyId. Those order should then have the field ClientDesc updated to match the Counterparty.DescriptionField. Once this is done I need to raise an event passing all the orders that have been updated.

The OrderCache is a dictionary in case that is not obvious.

Here is the existing code:

var updates = new List<Order>();
        lock (CacheLock)
        {
            counterpartyStatic.ToList().ForEach(cachedList =>
                cachedList.ToList().ForEach(
                    counterparty =>
                    {
                        var orders = OrderCache.Where(kvp => kvp.Value.Client == counterparty.CounterpartyId);
                        orders.ToList().ForEach(kvp =>
                        {
                            kvp.Value.ClientDesc = counterparty.Description;
                            updates.Add(kvp.Value);
                        });
                    }));
        }

        RaiseEvent(updates);

Thanks for any help

Answer 1

Given that your “query” is really intended to cause side effects (ie: you’re changing the value’s ClientDesc in a deep nested loop), I would suggest writing this using loops instead of trying to use LINQ. This has a couple of advantages – you’re not making lists just to use List<T>.ForEach, and the intention is far more clear:

var updates = new List<Order>();

lock (CacheLock)
{
    foreach(var cachedList in counterpartyStatic)
    {
        foreach(var counterparty in cachedList)
        {
             var orders = OrderCache.Where(kvp => kvp.Value.Client == counterparty.CounterpartyId);
             foreach(var kvp in orders)
             {
                  kvp.Value.ClientDesc = counterparty.Description;
                  updates.Add(kvp.Value);
             }
         }
    }

    RaiseEvent(updates);
}

This is just as short as your original, but far more clear in terms of what is happening.

For an argument on why avoiding List<T>.ForEach can be beneficial, see Eric Lippert’s “foreach” vs “ForEach”. List<T>.ForEach has even been removed for the new Windows Store apps, given the issues surrounding it.