Ruby Science
Extract Partial
Extracting a partial is a technique used for removing complex or duplicated view code from your application. This is the equivalent of using long method and extract method in your views and templates.
Uses
- Removes duplicated code from views.
- Avoids shotgun surgery by forcing changes to happen in one place.
- Removes divergent change by removing a reason for the view to change.
- Groups common code.
- Reduces view size and complexity.
- Makes view logic easier to reuse, which makes it easier to avoid duplication.
Steps
- Create a new file for partial prefixed with an underscore (_filename.html.erb).
- Move common code into newly created file.
- Render the partial from the source file.
Example
Let’s revisit the view code for adding and editing questions.
Note: There are a few small differences in the files (the URL endpoint and the label on the submit button).
# app/views/questions/new.html.erb
<h1>Add Question</h1>
<%= simple_form_for @question, as: :question, url: survey_questions_path(@survey) do |form| -%>
<%= form.hidden_field :type %>
<%= form.input :title %>
<%= render "#{@question.to_partial_path}_form", question: @question, form: form %>
<%= form.submit 'Create Question' %>
<% end -%># app/views/questions/edit.html.erb
<h1>Edit Question</h1>
<%= simple_form_for @question, as: :question, url: question_path do |form| -%>
<%= form.hidden_field :type %>
<%= form.input :title %>
<%= render "#{@question.to_partial_path}_form", question: @question, form: form %>
<%= form.submit 'Update Question' %>
<% end -%>First, extract the common code into a partial, remove any instance
variables and use question and url as local
variables:
# app/views/questions/_form.html.erb
<%= simple_form_for question, as: :question, url: url do |form| -%>
<%= form.hidden_field :type %>
<%= form.input :title %>
<%= render "#{question.to_partial_path}_form", question: question, form: form %>
<%= form.submit %>
<% end -%>Move the submit button text into the locales file:
# config/locales/en.yml
en:
helpers:
submit:
question:
create: 'Create Question'
update: 'Update Question'Then render the partial from each of the views, passing in the values
for question and url:
# app/views/questions/new.html.erb
<h1>Add Question</h1>
<%= render 'form', question: @question, url: survey_questions_path(@survey) %># app/views/questions/edit.html.erb
<h1>Edit Question</h1>
<%= render 'form', question: @question, url: question_path %>Next Steps
- Check for other occurrences of the duplicated view code in your application and replace them with the newly extracted partial.
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