Does not get exception when collection is empty with Sum method and Nhibernate

c#, iqueryable, linq, nhibernate, sum

Solution

You need to cast `Value` to a nullable type.

For example, assuming `Value` is an `int` property:

var result = MyQueryable()
                 .Where(x => x.IsDone)
                 .Select(x => (int?)x.Value)
                 .Sum()
             ?? 0;

Since a `Sum()` on a nullable enumerable will return null for an empty source, the coalesce operator (`??`) takes care of returning 0 when that happens.

Problem

I have a `IQueryable` with NHibernate and I would like to have an linq query to sum an specific column, but, when my condition on `Where` method give me an empty result I do not want to get an exception, but I would not like to hit an query to get all records and after it sum on memory, I would like something like `coalese` sql command, for sample: ``` // I get exception when its empty var query = MyQueryable() .Where(x => x.IsDone) .Select(x => x.Value) .Sum(); ``` I have to do something like this: ``` // I get 0, its ok, but ToList(), list all records on memory, // I just want to get a single value var query = MyQueryable() .Where(x => x.IsDone) .Select(x => x.Value) .ToList() .Sum(); ``` Is there any way? Thank you.

Original source