add association calculation method to order by results of a sql funct…

…ion on a column of a joined table

README.md

@@ -56,6 +56,7 @@ Assuming a database schema...
         create_table :comments, :force => true do |t|
           t.integer :user_id
           t.text :description
+          t.integer :rating
           t.timestamps
         end
       end
@@ -71,6 +72,7 @@ And some basic model declarations...
       has_ranking :comments
       has_recent_records :comments
       has_recent_records :articles, :comments
+      has_calculated_records :comments, :on => :rating
     end
 
     class Post < ActiveRecord::Base
@@ -199,6 +201,16 @@ Records with associated records since a certain time...
     User.recent_comments_and_posts_since(3.days.ago)
     User.recent_comments_or_posts_since(4.days.ago)
 
+Records with highest and lowest association column average...
+
+    User.by_comments_highest_rating_average
+    User.by_comments_lowest_rating_average
+
+Records with highest and lowest association column total...
+
+    User.by_comments_highest_rating_total
+    User.by_comments_lowest_rating_total
+
 State columns
 -------------
 

lib/pacecar/associations.rb

@@ -6,6 +6,25 @@ def self.included(base)
 
     module ClassMethods
 
+      def has_calculated_records(*names)
+        opts = names.extract_options!
+        names.each do |name|
+          *columns = opts[:on] || []
+          columns.flatten.each do |column|
+            { 'highest' => 'desc', 'lowest' => 'asc' }.each do |direction_name, direction|
+              { 'average' => 'avg', 'total' => 'sum' }.each do |function_name, function_method|
+                scope "by_#{name}_#{direction_name}_#{column}_#{function_name}".to_sym, {
+                  :select => "#{quoted_table_name}.*, #{function_method}(#{connection.quote_table_name(name)}.#{connection.quote_column_name column}) as #{name}_#{column}_#{function_name}",
+                  :joins => "inner join #{connection.quote_table_name(name)} on #{connection.quote_table_name(name)}.#{connection.quote_column_name reflections[name.to_sym].primary_key_name} = #{quoted_table_name}.#{connection.quote_column_name primary_key}",
+                  :group => safe_column_names.collect { |column_name| "#{quoted_table_name}.#{connection.quote_column_name(column_name)}" }.join(', '),
+                  :order => "#{name}_#{column}_#{function_name} #{direction}"
+                }
+              end
+            end
+          end
+        end
+      end
+
       def has_recent_records(*names)
         names.each do |name|
           scope "recent_#{name}_since".to_sym, lambda { |since|

spec/associations_spec.rb

@@ -1,6 +1,6 @@
 require 'spec_helper'
 
-describe 'Associations' do
+describe 'Associations', 'has recent records' do
 
   before do
     @comment_user = Factory :user
@@ -30,3 +30,40 @@
   end
 
 end
+
+
+describe 'Associations', 'has calculated records' do
+  before do
+    @user_one = Factory :user
+    @user_two = Factory :user
+    Factory :comment, :user => @user_one, :rating => 8
+    Factory :comment, :user => @user_one, :rating => 6
+    Factory :comment, :user => @user_two, :rating => 4
+    Factory :comment, :user => @user_two, :rating => 3
+    Factory :comment, :user => @user_two, :rating => 2
+  end
+  it "should order records based on association column highest average" do
+    output = User.by_comments_highest_rating_average
+    output.should == [@user_one, @user_two]
+    output.first.comments_rating_average.to_i.should == 7
+    output.last.comments_rating_average.to_i.should == 3
+  end
+  it "should order records based on association column lowest average" do
+    output = User.by_comments_lowest_rating_average
+    output.should == [@user_two, @user_one]
+    output.first.comments_rating_average.to_i.should == 3
+    output.last.comments_rating_average.to_i.should == 7
+  end
+  it "should order records based on association column highest total" do
+    output = User.by_comments_highest_rating_total
+    output.should == [@user_one, @user_two]
+    output.first.comments_rating_total.to_i.should == 14
+    output.last.comments_rating_total.to_i.should == 9
+  end
+  it "should order records based on association column lowest total" do
+    output = User.by_comments_lowest_rating_total
+    output.should == [@user_two, @user_one]
+    output.first.comments_rating_total.to_i.should == 9
+    output.last.comments_rating_total.to_i.should == 14
+  end
+end

spec/dummy/app/models/user.rb

@@ -9,5 +9,6 @@ class User < ActiveRecord::Base
   has_ranking :comments
   has_recent_records :comments
   has_recent_records :posts, :comments
+  has_calculated_records :comments, :on => :rating
 
 end

spec/dummy/db/migrate/20100419201348_create_schema.rb

@@ -24,6 +24,7 @@ def self.up
     create_table :comments, :force => true do |t|
       t.integer :user_id
       t.text :description
+      t.integer :rating
       t.timestamps
     end
     create_table :mammals, :force => true do |t|

spec/helpers_spec.rb

@@ -14,7 +14,7 @@
 
   describe "A class with a db table" do
     it "should  should return columns for #safe_column_names" do
-      Comment.safe_column_names.should == ['id', 'user_id', 'description', 'created_at', 'updated_at']
+      Comment.safe_column_names.should == ['id', 'user_id', 'description', 'rating', 'created_at', 'updated_at']
     end
   end
 

spec/ranking_spec.rb

@@ -11,11 +11,17 @@
   end
 
   it "should set the correct expected values on a maximum_ column method" do
-    User.maximum_comments.should == [@many, @few]
+    output = User.maximum_comments
+    output.should == [@many, @few]
+    output.first.comments_count.to_i.should == 5
+    output.last.comments_count.to_i.should == 2
   end
 
   it "should set the correct expected values on a minimum_ column method" do
-    User.minimum_comments.should == [@few, @many]
+    output = User.minimum_comments
+    output.should == [@few, @many]
+    output.first.comments_count.to_i.should == 2
+    output.last.comments_count.to_i.should == 5
   end
 
 end