Merge pull request #388 from mattvague/42-form-builder-breaks-on-poly…

…morphic-associations

Form builder no longer breaks on polymorphic associations. Closes #42

lib/active_admin/form_builder.rb

@@ -20,7 +20,9 @@ def inputs(*args, &block)
     # The input method returns a properly formatted string for
     # its contents, so we want to skip the internal buffering
     # while building up its contents
-    def input(*args)
+    def input(method, *args)
+      return if polymorphic_belongs_to_association?(method)
+
       content = with_new_form_buffer { super }
       return content.html_safe unless @inputs_with_block
       form_buffers.last << content.html_safe
@@ -98,6 +100,13 @@ def has_many(association, options = {}, &block)
 
     private
 
+    # Pass in a method to check if it's a polymorphic association
+    def polymorphic_belongs_to_association?(method)
+      reflection = reflection_for(method)
+
+      reflection && reflection.macro == :belongs_to && reflection.options[:polymorphic]
+    end
+
     def with_new_form_buffer
       form_buffers << "".html_safe
       return_value = yield

spec/unit/form_builder_spec.rb

@@ -64,6 +64,23 @@ def build_form(options = {}, &block)
     end
   end
 
+  context "when polymorphic relationship" do
+
+    let(:body) do
+      comment = ActiveAdmin::Comment.new
+
+      active_admin_form_for comment, :url => "admins/comments" do |f|
+        f.inputs :resource
+      end
+
+    end
+
+    it "should not generate any field" do
+      body.should have_tag("form", :attributes => { :method => 'post' })
+      body.should_not have_tag("select")
+    end
+  end
+
   describe "passing in options" do
     let :body do
       build_form :html => { :multipart => true } do |f|