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Calling partials through helpers

April 3rd, 2008

Rails partials are are fragments of template code that can be inserted into a view. They can really simplify template code, by factoring out repeated code.

For example, I often put forms into a partial so that the form can be shared be create and edit views:

quizzes/new.html.haml 
= error_messages_for :quiz
- form_for :quiz, @quiz, :url => quizzes_path, :html => {:method => :post} do |form|
  = render :partial => 'quizzes/form', :locals => {:form => form}
  = submit_tag 'Create'
quizzes/edit.html.haml 
= error_messages_for :quiz
- form_for :quiz, @quiz, :url => quiz_path(@quiz), :html => {:method => :put} do |form|
  = render :partial => 'quizzes/form', :locals => {:form => form}
  = submit_tag 'Update'

Many (most) people put the render call directly in their templates. This is not a good idea! What if you want to change the template path, or conditionally render a different template in certain conditions? Now you've got to repeat yourself in both templates, and that's bad news.

A simple way to fix this is to *always* use a helper to render the partial. That way any changes can be made in one place, and it also a great place to store any messy conditional logic so that it doesn't clutter up your templates.

quizzes/new.html.haml 
= error_messages_for :quiz
- form_for :quiz, @quiz, :url => quizzes_path, :html => {:method => :post} do |form|
  = quiz_form(form)
  = submit_tag 'Create'
quizzes/edit.html.haml 
= error_messages_for :quiz
- form_for :quiz, @quiz, :url => quiz_path(@quiz), :html => {:method => :put} do |form|
  = quiz_form(form)
  = submit_tag 'Update
quizzes_helper.rb 
def quiz_form(form)
   render :partial => 'quizzes/form', :locals => {:form => form}
end

Now if I want to do something, like say render a different form depending on a user's preference, it's easy to do.

quizzes/new.html.haml 
= error_messages_for :quiz
- form_for :quiz, @quiz, :url => quizzes_path, :html => {:method => :post} do |form|
  = quiz_form(form, current_user)
  = submit_tag 'Create'
quizzes_helper.rb 
def quiz_form(form, user = nil)
   if(!user.nil? && user.wants_advanced_quizzes))
     render :partial => 'quizzes/advanced_form', :locals => {:form => form}
   else
     render :partial => 'quizzes/form', :locals => {:form => form}
   end
end
This article is also published on "Learnhub":http://rails.learnhub.com/lesson/page/3400-calling-partials-through-helpers
Posted by Wesley Filed in Archive

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