Concat/Union Tables in LINQ

Question

This current project is more of a proof of concept for a larger project. I have two \"tables\" (represented as lists below), CatList and DogList, t

Answer 1

The issue is that the compiler can't figure out that by concatenating a List<Dog> and a List<Cat> it should produce a collection of iAnimals. By default it sees a List<Dog> and expects the following collection to be a collection of Dog too.

You can explicitly tell to treat everything as an iAnimal this by providing the generic parameter to Concat, i.e.

var result = DogList.Concat<iAnimal>(CatList);

You then get a result of type IEnumerable<iAnimal>.

Edit: If you're stuck on .NET 3.5, you'll need something like

var result = DogList.Cast<IAnimal>().Concat(CatList.Cast<IAnimal>());

as 3.5 can't automatically convert collection of something that inherits iAnimal to collection of iAnimal.

Answer 2

The generic lists are from different types (Dog and Cat), you have to "cast" them to the target interface before concatenation:

var list1 = DogList.Cast<IAnimal>();
var list2 = CatList.Cast<IAnimal>();

var bothLists = list1.Concat(list2); //optional .ToList()