I have a query in LINQ where I use SumAsync , however when my entity is empty I have the exception:
The cast to value type 'System.Decimal' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type.
The query I'm trying to do is as follows
var valor = await db.Exemplos.SumAsync(a => a.Valor);
How can I work around this and make SumAsync return 0 if my entity does not have data yet?
What happens is that Sum is being called in IQueryable and this causes the execution of this method to be delegated to the provider of Queryable , ie - as you you should already know, who runs Sum , in fact, is SQL Server. You can see this behavior in the source code in referencesource a>.
The error pops up just because SQL Server returns NULL when trying to execute a SUM on an "empty collection".
You can cast the cast from a.Valor to decimal? ( coalesce in the final result.
var valor = await db.Exemplos.SumAsync(a => (decimal?) a.Valor) ?? 0;