CODEWITHSUNDEEP
c#.netlinq
Milan Gatyás
Milan Gatyás

Reputation: 2777

Func parameter in LINQ expression

I have problem with Func delegate in LINQ expression. This is the problematic part of the method (repository.Items is IQueryable<T>) :

public static ActionResult XXX<T>(IRepository<T> repository,
        Func<T, int> keyExtractor, int id = 0)
    {
        if (id == 0) return ...
        T item = repository.Items.Where(x => keyExtractor(x) == id).
           FirstOrDefault();
        if (item == null) return ...
        try {
            repository.DeleteItem(item);
            return ...
        } catch (Exception e) {
            return ...
        }
    }

But when i run the method, i get error like type of node is not supported in LINQ entities. I tried also version with predikate but i had no luck at all.

Any ideas how to fix it?

I find out one possible way. LINQ performs delayed execution so i must first enforce execution like this:

T item = repository.Items.AsEnumerable().Where(x => keyExtractor(x) == id)

Upvotes: 2

Views: 2757

Answers (1)

Rapha&#235;l Althaus
Rapha&#235;l Althaus

Reputation: 60493

If you want to work on a IQueryable<T>, your argument must be an Expression<Func<T, int>>, not a Func<T, int>.

Func<T, int> will work with an IEnumerable<T>.

Where extensions methods has the same name for IQueryable<T> and IEnumerable<T>, but not the same arguments...

(by the way you could write repository.Items.FirstOrDefault(x => keyExtractor(x) == id);

Upvotes: 5

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