gistfile1.rb

# renders a post[author_attributes][login]
form_for(@new_post) do |post|
  post.fields_for(:author) do |author|
    concat(author.text_field(:login))
  end
end

# renders a post[author][login]
form_for(@new_post) do |post|
  post.fields_for(@new_post.author) do |author|
    concat(author.text_field(:login))
  end
end

# renders a post[author_attributes][login]
semantic_form_for(@new_post) do |post|
  post.semantic_fields_for(:author) do |author|
    concat(author.text_field(:login))
  end
end

# renders a post[author_attributes][login]
semantic_form_for(@new_post) do |post|
  post.inputs :for => :author do |author|
    concat(author.input(:login))
  end
end

# renders a post[author_attributes][login]
semantic_form_for(@new_post) do |post|
  post.inputs :for => [:author, @new_post.author] do |author|
    concat(author.input(:login))
  end
end

# renders a post[author][login]
semantic_form_for(@new_post) do |post|
  post.inputs :for => @new_post.author do |author|
    concat(author.input(:login))
  end
end

output_buffer.should have_tag("form input[@name='post[author_attributes][login]']", :count => 4)
output_buffer.should have_tag("form input[@name='post[author][login]']", :count => 2)