Reference ancestor_hierarchies in depth instead of ancestors (#398)

* Reference ancestor_hierarchies in depth instead of ancestors

* Update CHANGELOG.md

Author: weilandia

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### 8.0.0
 
 - Drop support to EOL ruby and rails
+- Reference ancestor_hierarchies in depth instead of ancestors to avoid n+1
 
 ## [7.4.0](https://github.com/ClosureTree/closure_tree/tree/7.4.0)
 

lib/closure_tree/model.rb

@@ -77,7 +77,7 @@ def leaves
     end
 
     def depth
-      ancestors.size
+      ancestor_hierarchies.size
     end
 
     alias_method :level, :depth