Linq query recursion

Question

I work in C# and Entity framework. I have a table in my database named Genre. Here are its attributes: idGenre, name, idParentGenre.

For example. the values would be:

(idGenre = 1, name = "acoustic", idParentGenre=2)

(idGenre = 2, name = "rock", idParentGenre=2)

(idGenre = 3, name = "country", idParentGenre=4)

(idGenre = 4, name = "folk", idParentGenre=5)

(idGenre = 5, name = "someOtherGenre", idParentGenre=5)

As you can see, it's kind of a tree.

Now, I have a method for searching through this table. The input parameter is idGenre and idParentGenre. I should return if the genre (idGenre) is a son/grandchild/grandgrandchild/... of idParentGenre.

For example, I get idGenre=3, idParentGenre=5, I should return true.

However, there isn't recursion in Linq. Is there a way I can do this?

Answer 1

I would make a method to handle this instead of using LINQ:

bool HasParent(int genre, int parent)
{
    Genre item = db.Genres.FirstOrDefault(g => g.IdGenre == genre);
    if (item == null)
        return false;

    // If there is no parent, return false, 
    // this is assuming it's defined as int?
    if (!item.idParentGenre.HasValue)
        return false;

    if (item.idParentGenre.Value == parent)
        return true;

    return HasParent(item.idParentGenre, parent);
}

This lets you handle this in a single recursive function.