Merge pull request #23 from MichalPokorny/leaves-scope

Add leaves scope

lib/acts_as_tree.rb

@@ -94,15 +94,35 @@ def acts_as_tree(options = {})
 
         after_update :update_parents_counter_cache
 
-        def self.roots
+        def self.default_tree_order
           order_option = %Q{#{configuration.fetch :order, "nil"}}
-          where(:#{configuration[:foreign_key]} => nil).order(order_option)
+          order(order_option)
         end
 
         def self.root
           self.roots.first
         end
+
+        def self.roots
+          where(:#{configuration[:foreign_key]} => nil).default_tree_order
+        end
       EOV
+
+      if configuration[:counter_cache]
+        class_eval <<-EOV
+          def self.leaves
+            where(:children_count => 0).default_tree_order
+          end
+        EOV
+      else
+        # Fallback to less efficent ways to find leaves.
+        class_eval <<-EOV
+          def self.leaves
+            internal_ids = select(:#{configuration[:foreign_key]}).where(arel_table[:#{configuration[:foreign_key]}].not_eq(nil))
+            where("id NOT IN (\#{internal_ids.to_sql})").default_tree_order
+          end
+        EOV
+      end
     end
 
   end

test/acts_as_tree_test.rb

@@ -67,6 +67,7 @@ class TreeTest < MiniTest::Unit::TestCase
 
   def setup
     setup_db
+
     @root1              = TreeMixin.create!
     @root_child1        = TreeMixin.create! parent_id: @root1.id
     @child1_child       = TreeMixin.create! parent_id: @root_child1.id
@@ -139,6 +140,14 @@ def test_roots
     assert_equal [@root1, @root2, @root3], TreeMixin.roots
   end
 
+  def test_leaves
+    assert_equal [@child1_child_child, @root_child2, @root2, @root3], TreeMixin.leaves
+  end
+
+  def test_default_tree_order
+    assert_equal [@root1, @root_child1, @child1_child, @child1_child_child, @root_child2, @root2, @root3], TreeMixin.default_tree_order
+  end
+
   def test_siblings
     assert_equal [@root2, @root3], @root1.siblings
     assert_equal [@root_child2], @root_child1.siblings
@@ -408,4 +417,7 @@ def test_update_parents_counter_cache
     assert_equal 0, @child1.reload.children_count
   end
 
+  def test_leaves
+    assert_equal [@child1_child1, @child2], TreeMixinWithCounterCache.leaves
+  end
 end