Question

I am trying to do something like this:

from t in ent.myEntities
where SelectedProperties == null || SelectedProperties.Any(le => le == t.Entity)
select t

basically trying to cover 2 cases. accepting an empty list, should return all entities, or filter on the list if it is supplied.

above actually does work when i supply the list, however in the case when it is null i get:

Unable to create a constant value of type
‘System.Collections.Generic.List`1’. Only primitive types (‘such as
Int32, String, and Guid’) are supported in this context

also tried using this with a string array:

where arr == null || arr.Contains(t.Entity)

is it possible to have such a condition without having to build a predicate (which is a bigger effort)?

Answer 1

You might want to try using the list in a simpler way:

where SelectedProperties == null || SelectedProperties.Contains(t.Entity)

It may well not work, but it’s worth a try. Otherwise, if this is really your whole query, I’d just write it as:

var query = SelectedProperties == null 
            ? ent.myEntities
            : ent.myEntities.Where(t => SelectedProperties.Contains(t.Entity));

EDIT: Okay, if you have to use Any, and have lots of these to compose, you can do it like this:

var query = ent.myEntities;
if (SelectedProperties != null)
{
    query = query.Where(t => SelectedProperties.Any(x => x == t.Entity));
}
if (SomethingElse)
{
    query = query.Where(...);
}
// etc