linq how to select the parent from a collection where the parent contains child items in another collection

Question

I have an observable collection ie Owners and that collection has child items ie Dogs.

Now given another collection of local Dogs how can I select all the Owners where there Dogs exist in my local Dogs collection. The equality condition would be that the Dog == Dog.

Answer 1

The following line should do the trick. This will give you all owners where at least one of their dogs is in the local list.

owners.Where(owner => owner.Dogs.Any(dog => localDogs.Contains(dog)))

If you only want the owners where all their dogs are in the local list, then use the following.

owners.Where(owner => owner.Dogs.All(dog => localDogs.Contains(dog)))

The tiny difference is Any()vs. All().