Nicer error message on has_many :through when :through reflection can not be found (closes #4042) [court3nay@gmail.com]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@3910 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

@@ -47,6 +47,8 @@
       has_many :attachments, :as => :attachable, :dependent => :delete_all
     end
 
+* Nicer error message on has_many :through when :through reflection can not be found. #4042 [court3nay@gmail.com]
+
 * Upgrade to Transaction::Simple 1.3 [Jamis Buck]
 
 * Catch FixtureClassNotFound when using instantiated fixtures on a fixture that has no ActiveRecord model [Rick Olson]

activerecord/lib/active_record/associations/has_many_through_association.rb

@@ -61,7 +61,9 @@ module ActiveRecord
         end
 
         def construct_conditions
-          through_reflection = @owner.class.reflections[@reflection.options[:through]]
+          unless through_reflection = @owner.class.reflections[@reflection.options[:through]]
+            raise ActiveRecordError, "Could not find the association '#{@reflection.options[:through]}' in model #{@reflection.klass}"
+          end
           
           if through_reflection.options[:as]
             conditions = 

activerecord/test/associations_join_model_test.rb

@@ -207,6 +207,10 @@ class AssociationsJoinModelTest < Test::Unit::TestCase
     assert posts(:welcome, :reload)[:taggings_count].zero?
   end
 
+  def test_unavailable_through_reflection
+    assert_raises (ActiveRecord::ActiveRecordError) { authors(:david).nothings }
+  end
+
   private
     # create dynamic Post models to allow different dependency options
     def find_post_with_dependency(post_id, association, association_name, dependency)

activerecord/test/fixtures/author.rb

@@ -22,6 +22,8 @@ class Author < ActiveRecord::Base
 
   has_many :categorizations
   has_many :categories, :through => :categorizations
+  
+  has_many :nothings, :through => :kateggorisatons, :class_name => 'Category'
 
   attr_accessor :post_log