add balance methods to boolean module

README.rdoc

@@ -108,6 +108,10 @@ Records that are all admins or non-admins...
   User.admin
   User.not_admin
 
+The "balance" (count of true minus false for column in question)...
+
+  User.admin_balance
+
 = Datetime columns
 
 Records approved before or after certain times...

lib/pacecar/boolean.rb

@@ -7,6 +7,7 @@ def self.included(base)
     module ClassMethods
       def self.extended(base)
         base.send :define_boolean_scopes
+        base.send :define_balance_count
       end
 
       protected
@@ -18,6 +19,16 @@ def define_boolean_scopes
         end
       end
 
+      def define_balance_count
+        boolean_column_names.each do |name|
+          self.class_eval %Q{
+            def self.#{name}_balance
+              #{name}.count - not_#{name}.count
+            end
+          }
+        end
+      end
+
     end
   end
 end

test/boolean_test.rb

@@ -16,6 +16,25 @@ class BooleanTest < Test::Unit::TestCase
       proxy_options = { :conditions => ['"users".admin = ?', false] }
       assert_equal proxy_options, @class.not_admin.proxy_options
     end
+    context "With boolean column scopes that can count" do
+      setup do
+        assert @class.respond_to?(:admin_balance)
+        @true_mock = mock
+        @false_mock = mock
+        @class.expects(:admin).returns @true_mock
+        @class.expects(:not_admin).returns @false_mock
+      end
+      should "return correct value for balance class method when true greater than false" do
+        @true_mock.expects(:count).returns 5
+        @false_mock.expects(:count).returns 2
+        assert_equal 3, @class.admin_balance
+      end
+      should "return correct value for balance class method when true less than false" do
+        @true_mock.expects(:count).returns 2
+        @false_mock.expects(:count).returns 5
+        assert_equal -3, @class.admin_balance
+      end
+    end
   end
 
 end