fields_for should treat ActiveRecord::Relation as an array

[#5795 state:resolved]

Signed-off-by: José Valim <jose.valim@gmail.com>

3 files changed, 33 insertions, 2 deletions

diff --git a/actionpack/lib/action_view/helpers/form_helper.rb b/actionpack/lib/action_view/helpers/form_helper.rb
index 80a872068d..0470b051c6 100644
--- a/actionpack/lib/action_view/helpers/form_helper.rb
+++ b/actionpack/lib/action_view/helpers/form_helper.rb
@@ -1277,11 +1277,11 @@ module ActionView
 
           if association.respond_to?(:persisted?)
             association = [association] if @object.send(association_name).is_a?(Array)
-          elsif !association.is_a?(Array)
+          elsif !association.respond_to?(:to_ary)
             association = @object.send(association_name)
           end
 
-          if association.is_a?(Array)
+          if association.respond_to?(:to_ary)
             explicit_child_index = options[:child_index]
             output = ActiveSupport::SafeBuffer.new
             association.each do |child|
diff --git a/actionpack/test/lib/controller/fake_models.rb b/actionpack/test/lib/controller/fake_models.rb
index dba632e6df..ae0c38184d 100644
--- a/actionpack/test/lib/controller/fake_models.rb
+++ b/actionpack/test/lib/controller/fake_models.rb
@@ -184,3 +184,13 @@ module Blog
     end
   end
 end
+
+class ArelLike
+  def to_ary
+    true
+  end
+  def each
+    a = Array.new(2) { |id| Comment.new(id + 1) }
+    a.each { |i| yield i }
+  end
+end
diff --git a/actionpack/test/template/form_helper_test.rb b/actionpack/test/template/form_helper_test.rb
index acb6e7aa64..2c60096475 100644
--- a/actionpack/test/template/form_helper_test.rb
+++ b/actionpack/test/template/form_helper_test.rb
@@ -1230,6 +1230,27 @@ class FormHelperTest < ActionView::TestCase
     assert_dom_equal expected, output_buffer
   end
 
+  def test_nested_fields_for_arel_like
+    @post.comments = ArelLike.new
+
+    form_for(@post) do |f|
+      concat f.text_field(:title)
+      concat f.fields_for(:comments, @post.comments) { |cf|
+        concat cf.text_field(:name)
+      }
+    end
+
+    expected = whole_form('/posts/123', 'edit_post_123', 'edit_post', :method => 'put') do
+      '<input name="post[title]" size="30" type="text" id="post_title" value="Hello World" />' +
+      '<input id="post_comments_attributes_0_name" name="post[comments_attributes][0][name]" size="30" type="text" value="comment #1" />' +
+      '<input id="post_comments_attributes_0_id" name="post[comments_attributes][0][id]" type="hidden" value="1" />' +
+      '<input id="post_comments_attributes_1_name" name="post[comments_attributes][1][name]" size="30" type="text" value="comment #2" />' +
+      '<input id="post_comments_attributes_1_id" name="post[comments_attributes][1][id]" type="hidden" value="2" />'
+    end
+
+    assert_dom_equal expected, output_buffer
+  end
+
   def test_nested_fields_for_with_existing_records_on_a_supplied_nested_attributes_collection_different_from_record_one
     comments = Array.new(2) { |id| Comment.new(id + 1) }
     @post.comments = []