Correct way to retrieve a sum of the earnest money deposits

[kwesterlage]

We are (successfully in many cases) using this code to retrieve the difference between the amount of earnest money kept vs returned for an order:

Code: Select all

((IEnumerable<dynamic>)order.SalesContract?.EarnestMoney.Deposits)?.Sum(x => (decimal)x.Amount - (decimal)x.AmountReturnedToBuyer) ?? 0;

Sometimes this code returns strange errors, like:
"Index was out of range. Must be non-negative and less than the size of the collection."
or "Cannot use a lambda expression as an argument to a dynamically dispatched operation without first casting it to a delegate or expression tree type."

What is the correct and reliable way to sum the difference between the kept and returned amount for all earnest money deposits on an order?

[BobRichards]

Dynamic types are handy tool and we use them also. However, all types used in LINQ expression must be resolved at compile time (even when using dynamic types) and the c# compiler cannot see the most of the types in the Select order model so it might guess incorrectly (or usually throws up its hands and says "Cannot use a lambda expression as an argument to a dynamically dispatched operation without first casting it to a delegate or expression tree type").

The best approach (and *slightly* faster) is to use the IOrderItem interface to get property values. As you will see below, the inner loop still uses dynamic typing because it is so handy.

Code: Select all

// Initialize summation.
decimal amount = 0;

// Get deposits and sum amount of deposit retained.
IOrderItem salesContract = (IOrderItem)iOrder.GetProperty("SalesContract");
if (salesContract != null)
{
	IOrderItem earnestMoney = (IOrderItem)salesContract.GetProperty("EarnestMoney");
	IList deposits = (IList)earnestMoney.GetProperty("Deposits");
	foreach (dynamic deposit in deposits)
	{
		amount += deposit.Amount - deposit.AmountReturnedToBuyer;
	}
}