1. Introduction

• This tutorial aims to guide you in displaying data using partial views in Ruby on Rails. Partial views are a powerful feature of Rails that allow you to break your code into reusable chunks. These can be especially useful when you have code that you need to use in multiple places, such as forms or error messages.
• By the end of this tutorial, you will have learned how to create and use partial views to display data and error messages.
• Prerequisites: You should have some basic knowledge of Ruby on Rails.

2. Step-by-Step Guide

• Partial Views: In Rails, a partial view is a file containing code that can be reused in other views. The naming convention for a partial view is to prepend it with an underscore (_). For example, _form.html.erb.
• Rendering Partial Views: To display a partial view in another view, you use the render method, like so: <%= render 'form' %>. This will look for a file named _form.html.erb in the same directory as the view from where it's being called.
• Passing Data to Partials: You can pass local data to a partial like this: <%= render 'form', local_variable: @instance_variable %>.
• Handling Error Messages: Rails automatically wraps fields that contain an error with a div with a class of field_with_errors. You can customize this to display error messages to users.

3. Code Examples

• Example 1: Creating a Partial View

Create a file named _form.html.erb in the app/views/users directory and add the following code:

<%= form_with(model: user, local: true) do |form| %>
  <% if user.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(user.errors.count, "error") %> prohibited this user from being saved:</h2>
      <ul>
      <% user.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= form.label :name %>
    <%= form.text_field :name, id: :user_name %>
  </div>

  <div class="actions">
    <%= form.submit %>
  </div>
<% end %>

• Example 2: Using the Partial View

In your new.html.erb and edit.html.erb views for the User model, you can now render the form like this:

<%= render 'form', user: @user %>

4. Summary

• Partial views in Rails allow you to reuse code in different views.
• You can pass local data to partials, which is especially useful for displaying forms.
• Rails provides a built-in mechanism for handling and displaying error messages.

5. Practice Exercises

1. Exercise: Create a partial view for a comment form and use it in the new and edit views.

2. Solution:

   • Create _comment_form.html.erb in app/views/comments and add your form code.
   • In new.html.erb and edit.html.erb, add <%= render 'comment_form', comment: @comment %>.

3. Exercise: Display a list of error messages in a partial view.

4. Solution:
   • Create _errors.html.erb in app/views/shared and add code to display error messages.
   • In any view where you want to display errors, add <%= render 'shared/errors', object: @object %>.

Remember to practice regularly and revisit these concepts to solidify them in your memory. Happy coding!