Fixes .sort_by_ancestry with custom ancestry_column

lib/ancestry/class_methods.rb

@@ -98,7 +98,7 @@ def sort_by_ancestry(nodes, &block)
 
       unless arranged
         presorted_nodes = nodes.sort do |a, b|
-          rank = (a.ancestry || ' ') <=> (b.ancestry || ' ')
+          rank = (a.public_send(ancestry_column) || ' ') <=> (b.public_send(ancestry_column) || ' ')
           rank = yield(a, b) if rank == 0 && block_given?
           rank
         end

test/concerns/sort_by_ancestry_test.rb

@@ -233,4 +233,17 @@ def test_sort_by_ancestry_with_block_paginated_missing_parents_and_children
       end
     end
   end
+
+  def test_sort_by_ancestry_with_ancestry_column
+    AncestryTestDatabase.with_model :ancestry_column => :t1, :extra_columns => {:rank => :integer} do |model|
+      _, n2, n3, n4, n5, _ = build_ranked_tree(model)
+
+      records = model.sort_by_ancestry(model.all.ordered_by_ancestry_and(:rank).offset(1).take(4), &RANK_SORT)
+      if CORRECT
+        assert_equal [n3, n2, n4, n5].map(&:id), records.map(&:id)
+      else
+        assert_equal [n2, n4, n5, n3].map(&:id), records.map(&:id)
+      end
+    end
+  end
 end