How do I select recursive nested entities using LINQ to Entity

Question

I have an entity called Category and the entity contains a IEnumerable called ChildCategories. A category can have these child categories which can have it\'s own child cate

Answer 1

In his blog post Traverse a hierarchical structure with LINQ-to-Hierarchical , Arjan Einbu describes a method of flattening hierarchies for ease of querying:

Can I make a generic extension method that will flatten any hierarchy? [...]

To do that, we need to analyze which parts of the method needs to be swapped out. That would be the TreeNode’s Nodes property. Can we access that in an other way? Yes, I think a delegate can help us, so lets give it a try:

public static IEnumerable FlattenHierarchy(this T node, 
                             Func> getChildEnumerator)
{
    yield return node;
    if(getChildEnumerator(node) != null)
    {
        foreach(var child in getChildEnumerator(node))
        {
            foreach(var childOrDescendant 
                      in child.FlattenHierarchy(getChildEnumerator))
            {
                yield return childOrDescendant;
            }
        }
    }
}

casperOne describes this in his answer as well, along with the problems inherent in trying to traverse the hierarchy directly using LINQ.