Scope for leaves

lib/ancestry/class_methods.rb

@@ -17,6 +17,16 @@ def scope_depth depth_options, depth
       end
     end
 
+    # Scope that returns all the leaves
+    def leaves
+      id_column = "#{table_name}.id"
+      parent_ancestry = sql_concat("#{table_name}.#{ancestry_column}", "'/'", id_column)
+
+      joins("LEFT JOIN #{table_name} AS c ON c.#{ancestry_column} = #{sql_cast_as_text(id_column)} OR c.#{ancestry_column} = #{parent_ancestry}").
+        group(id_column).
+        having('COUNT(c.id) = 0')
+    end
+
     # Orphan strategy writer
     def orphan_strategy= orphan_strategy
       # Check value of orphan strategy, only rootify, adopt, restrict or destroy is allowed
@@ -197,5 +207,25 @@ def rebuild_depth_cache!
         end
       end
     end
+
+    private
+
+    def sql_concat *parts
+      if ActiveRecord::Base.connection.adapter_name.downcase == 'sqlite'
+        parts.join(' || ')
+      else
+        "CONCAT(#{parts.join(', ')})"
+      end
+    end
+
+    def sql_cast_as_text column
+      text_type = if ActiveRecord::Base.connection.adapter_name.downcase == 'mysql'
+        'CHAR'
+      else
+        'TEXT'
+      end
+
+      "CAST(#{column} AS #{text_type})"
+    end
   end
 end

lib/ancestry/has_ancestry.rb

@@ -86,4 +86,4 @@ class << ActiveRecord::Base
       alias_method :acts_as_tree, :has_ancestry
     end
   end
-end
+end

test/concerns/class_methods_test.rb

@@ -0,0 +1,33 @@
+require_relative '../environment'
+
+class ClassMethodsTest < ActiveSupport::TestCase
+  def test_sql_concat
+    AncestryTestDatabase.with_model do |model|
+      result = model.send(:sql_concat, 'table_name.id', "'/'")
+
+      case ActiveRecord::Base.connection.adapter_name.downcase.to_sym
+      when :sqlite
+        assert_equal result, "table_name.id || '/'"
+      when :mysql
+        assert_equal result, "CONCAT(table_name.id, '/')"
+      when :postgresql
+        assert_equal result, "CONCAT(table_name.id, '/')"
+      end
+    end
+  end
+
+  def text_sql_cast_as_text
+    AncestryTestDatabase.with_model do |model|
+      result = model.send(:sql_cast_as_text, 'table_name.id')
+
+      case ActiveRecord::Base.connection.adapter_name.downcase.to_sym
+      when :sqlite
+        assert_equal result, 'CAST(table_name.id AS TEXT)'
+      when :mysql
+        assert_equal result, 'CAST(table_name.id AS CHAR)'
+      when :postgresql
+        assert_equal result, 'CAST(table_name.id AS TEXT)'
+      end
+    end
+  end
+end

test/concerns/scopes_test.rb

@@ -6,6 +6,9 @@ def test_scopes
       # Roots assertion
       assert_equal roots.map(&:first), model.roots.to_a
 
+      # Leaves assertion
+      assert_equal model.all.select(&:is_childless?), model.leaves.order(:id).to_a
+
       model.all.each do |test_node|
         # Assertions for ancestors_of named scope
         assert_equal test_node.ancestors.to_a, model.ancestors_of(test_node).to_a
@@ -66,4 +69,4 @@ def test_scoping_in_callbacks
       assert child = parent.children.create
     end
   end
-end
+end