Merge pull request #10211 from neerajdotname/4208

fix respond_to? for non selected column

3 files changed, 41 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 278da322f2..e46ca3bd07 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,28 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   If a query selects only a few columns and gives custom names to
+    those columns then `respond_to?` was returning true for the non
+    selected columns. However calling those non selected columns
+    raises exception.
+
+        post = Post.select("'title' as post_title").first
+
+    In the above case when `post.body` is invoked then an exception is
+    raised since `body` attribute is not selected. Howevere `respond_to?`
+    did not behave correctly.
+
+        pos.respond_to?(:body) #=> true
+
+    Reason was that Active Record calls `super` to pass the call to
+    Active Model and all the columns are defined on Active Model.
+
+    Fix is to actually check if the data returned from the db contains
+    the data for column in question.
+
+    Fixes #4208.
+
+    *Neeraj Singh*
+
 *   Run `rake migrate:down` & `rake migrate:up` in transaction if database supports.
 
     *Alexander Bondarev*
diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index 22405c5d74..d0c51b77c2 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -163,8 +163,20 @@ module ActiveRecord
     #   person.respond_to('age?')   # => true
     #   person.respond_to(:nothing) # => false
     def respond_to?(name, include_private = false)
+      name = name.to_s
       self.class.define_attribute_methods unless self.class.attribute_methods_generated?
-      super
+      result = super
+
+      # If the result is false then it means this method is not supported by ActiveModel too
+      return false unless result
+
+      # If the result is true then check for the select case.
+      # For queries selecting a subset of columns, return false for unselected columns.
+      if @attributes.present? && self.class.column_names.include?(name)
+        return has_attribute?(name)
+      end
+
+      return true
     end
 
     # Returns +true+ if the given attribute is in the attributes hash, otherwise +false+.
diff --git a/activerecord/test/cases/relation_test.rb b/activerecord/test/cases/relation_test.rb
index 34ecdb3cc9..06723b9d7f 100644
--- a/activerecord/test/cases/relation_test.rb
+++ b/activerecord/test/cases/relation_test.rb
@@ -185,6 +185,11 @@ module ActiveRecord
       assert_equal 3, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count.length
     end
 
+    def test_respond_to_for_non_selected_element
+      post = Post.select("'title' as post_title").first
+      assert !post.respond_to?(:body), "post should not respond_to?(:body) since invoking it raises exception"
+    end
+
   end
 
   class RelationMutationTest < ActiveSupport::TestCase