Intersect LINQ query

Question

If I have an IEnumerable where ClassA exposes an ID property of type long. Is it possible to use a Linq query to get all instances of ClassA with ID belonging to a second IE

Answer 1

I will post an answer using Intersect.

This is useful if you want to intersect 2 IEnumerables of the same type.

First we will need an EqualityComparer:

    public class KeyEqualityComparer<T> : IEqualityComparer<T>
    {
        private readonly Func<T, object> keyExtractor;

        public KeyEqualityComparer(Func<T, object> keyExtractor)
        {
            this.keyExtractor = keyExtractor;
        }

        public bool Equals(T x, T y)
        {
            return this.keyExtractor(x).Equals(this.keyExtractor(y));
        }

        public int GetHashCode(T obj)
        {
            return this.keyExtractor(obj).GetHashCode();
        }
    }

Secondly we apply the KeyEqualityComparer to the Intersect function:

var list3= list1.Intersect(list2, new KeyEqualityComparer<ClassToCompare>(s => s.Id));