Custom intersect in lambda

Question

I would like to know if this is possible to solve using a lambda expression:

List<Foo> listOne = service.GetListOne();
List<Foo> listTwo = service.GetListTwo();
List<Foo> result = new List<Foo>();

foreach(var one in listOne)
{
    foreach(var two in listTwo)
    {
        if((one.Id == two.Id) && one.someKey != two.someKey)
           result.Add(one);
    }
}

Answer 1

Sure you can! You can use this overload of Linq's Intersect extension method which takes an IEqualityComparer<T>, like this:

public class FooComparer : IEqualityComparer<Foo> 
{
    public bool Equals(Foo x, Foo y)
    {
        return x.Id == y.Id && x.someKey != y.someKey;
    }

    public int GetHashCode(Foo x)
    {
        return x.Id.GetHashCode();
    }
}

...

var comparer = new FooComparer();
List<Foo> listOne = service.GetListOne();
List<Foo> listTwo = service.GetListTwo();
List<Foo> result = listOne.Intersect(listTwo, comparer).ToList();