Raise error when trying to add to a has_many :through association. Use the Join Model instead. [Rick]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4265 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

4 files changed, 31 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index 296070b865..89b23c1e96 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,10 @@
 *SVN*
 
+* Raise error when trying to add to a has_many :through association. [Rick]
+
+    @post.tags << @tag                  # BAD
+    @post.taggings.create(:tag => @tag) # GOOD
+
 * Allow all calculations to take the :include option, not just COUNT (closes #4840) [Rick]
 
 * Update inconsistent migrations documentation. #4683 [machomagna@gmail.com]
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 4a637d5dab..2861a3940b 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -66,6 +66,16 @@ module ActiveRecord
     end
   end
 
+  class ReadOnlyAssociation < ActiveRecordError #:nodoc:
+    def initialize(reflection)
+      @reflection = reflection
+    end
+  
+    def message
+      "Can not add to a has_many :through association.  Try adding to #{@reflection.through_reflection.name.inspect}."
+    end
+  end
+
   module Associations # :nodoc:
     def self.append_features(base)
       super
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 44054b42e1..8cafb26d44 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -8,7 +8,6 @@ module ActiveRecord
         construct_sql
       end
 
-
       def find(*args)
         options = Base.send(:extract_options_from_args!, args)
 
@@ -41,6 +40,14 @@ module ActiveRecord
         @loaded = false
       end
 
+      def <<(*args)
+        raise ActiveRecord::ReadOnlyAssociation, @reflection
+      end
+
+      [:push, :concat, :create, :build].each do |method|
+        alias_method method, :<<
+      end
+
       protected
         def method_missing(method, *args, &block)
           if @target.respond_to?(method) || (!@reflection.klass.respond_to?(method) && Class.respond_to?(method))
diff --git a/activerecord/test/associations_join_model_test.rb b/activerecord/test/associations_join_model_test.rb
index 93cfd0084c..9bacbfc717 100644
--- a/activerecord/test/associations_join_model_test.rb
+++ b/activerecord/test/associations_join_model_test.rb
@@ -357,6 +357,14 @@ class AssociationsJoinModelTest < Test::Unit::TestCase
     assert_nil posts(:thinking).tags.find_by_name("General").attributes["tag_id"]
   end
 
+  def test_raise_error_when_adding_to_has_many_through
+    assert_raise(ActiveRecord::ReadOnlyAssociation) { posts(:thinking).tags <<     tags(:general)  }
+    assert_raise(ActiveRecord::ReadOnlyAssociation) { posts(:thinking).tags.push   tags(:general)  }
+    assert_raise(ActiveRecord::ReadOnlyAssociation) { posts(:thinking).tags.concat tags(:general)  }
+    assert_raise(ActiveRecord::ReadOnlyAssociation) { posts(:thinking).tags.build(:name => 'foo')  }
+    assert_raise(ActiveRecord::ReadOnlyAssociation) { posts(:thinking).tags.create(:name => 'foo') }
+  end
+
   private
     # create dynamic Post models to allow different dependency options
     def find_post_with_dependency(post_id, association, association_name, dependency)