Rails method to get all descendant categories

Previously, I was shown a concise and excellent way to get all ancestor categories for a given category in a rails application:

def ancestors
  result = []
  c = self
 开发者_JS百科 while c.parent
    result.unshift(c.parent)
    c = c.parent
  end
  result
end   

Now I'm trying to figure out how to get all of the descendant categories for a given category (children, children of children, etc.) The nearest I've been able to get is the following, but I still have the problem where the final result array is messed up. The top level arrays aren't closed. I've been wrestling with this for hours and am not sure how to fix it.

def descendants

  result = []
  c = self

  for child in c.children
   result.push(child)
   if(child.children.any?)
    result.push(child.descendants)
   end
  end

  result

end

Try this:

def descendants
  children.map(&:descendants).flatten
end

def ancestors
  [parent, parent.try(:ancestors)].compact.flatten
end

Manual tree traversing has performance implications. You should consider using a gem like ancestry which does a very good job of tree representation.

Edit 1

If you are using the awesome_nested_set gem, please note that it has ancestors and descendants methods on AR instance. You can sort the results of these methods using ruby (If you are dealing with a small set < 100).

category.descendants.sort_by(&:name)

Also acts_as_tree is a great gem by Rails: https://github.com/rails/acts_as_tree

I use it for this very purpose and it automates it all.