Lesson: Generate Rails Scaffolding for Creating and Editing Books

This Tutorial is known to work with hydra-head version 6.0.0.
Please update this wiki to reflect any other versions that have been tested.

Goals

Explanation

Steps

Step: Set up Rails Scaffolding for creating and editing Books

We will use the Rails scaffold generator to set up the routes, Controller and Views we need in order to CRUD books.

Note: If you are not familiar with the ideas of Controllers, Views and routes, or aren't familiar with the Rails scaffold generator, go through the Railsbridge Curriculum and then come back to this lesson. You might also want to read the Getting Started with Rails guide.

Tell the generator to build scaffolding for the Book model and make it assume books have title and author attributes like the ones we set up in the Dive into Hydra tutorial.

rails generate scaffold Book title:string author:string

When it asks you whether to overwrite app/models/book.rb, enter n and hit enter.

The generator creates a few things that we don't want in the test and db directories. Delete them with the git clean command.

$> git clean -df test db
Removing db/migrate/20130417230046_create_books.rb
Removing test/fixtures/books.yml
Removing test/functional/books_controller_test.rb
Removing test/unit/book_test.rb
Removing test/unit/helpers/

Step: Commit your work

git add .
git commit -m"Ran scaffold generator"

Step: Run the server & Explore

Run the rails server and visit http://localhost:3000/books

Explore the pages for creating, editing and showing Books. You will notice that the Title and Author are being displayed strangely.

Title: ["Anna Karenina"]
Author: ["Tolstoy, Leo"]

This is because the scaffold generator assumed that tile and author were single-valued while Hydra defaults to making them multi-valued. There are two ways to fix this. The first way is to tell Hydra to make the field single-valued. The other way is to make your views handle multivalued fields. Let's try both.

Step: Make Title single-valued

In app/models/book.rb find the line that delegates the title field to the descMetadata datastream

   delegate :title, to: 'descMetadata'

Add an extra argument of unique: true at the end of the line.

   delegate :title, to: 'descMetadata', unique: true

Save the file and reload the pages in your browser. The Title will now show up properly, as a single-valued field.

Step: Make the Show page display Authors as a multi-valued field

In app/views/books/show.html.erb find the lines that display the author field.

<div class="field">
    <%= f.label :author %><br />
    <%= f.text_field :author %>
</div>

We want to make these lines iterate over the values returned by @book.author and put them in a list

<p>
  <b>Author(s):</b>
  <ul>
    <%- @book.author.each do |author|%>
      <li><%= author %></li>
    <%- end %>
  </ul>
</p>

Save the file and refresh the Show view for a book. Now authors show up as a list of values.

Step: Make the _form view partial display Authors as a multi-valued field

The _form partial defines the guts of the form that's used in both the new view and the edit view. That makes our lives simpler because we only have to update that one file to fix both pages!

In app/views/books/_form.html.erb find the lines that display the author field.

  <p>
    <b>Author:</b>
    <%= @book.author %>
  </p>

Replace those lines with something that iterates over the values from @book.author and displays a text_field tag for each of them. Note that the @name attribute will be set to "book[author][]". The trailing [] in the name tells Rails that this is a multivalued field that should be parsed as an Array.

  <%= f.label :author, "Authors" %>
  <% @book.author.each do |author| %>
    <div class="field">
      <%= text_field_tag "book[author][]", author %>
    </div>
  <% end %> 

This handles displaying existing author values, but what about setting the author value in the first place? If there are no values in the array, no fields are going to be displayed. As a stop-gap, we can add a conditional clause that displays an empty text_field when the array is empty.

  <%= f.label :author, "Authors" %>
  <% @book.author.each do |author| %>
    <div class="field">
      <%= text_field_tag "book[author][]", author %>
    </div>
  <% end %> 
  <%- if @book.author.empty? %>
    <div class="field">
      <%= text_field_tag "book[author][]", nil %>
    </div>
  <%- end %>

Note: This still doesn't cover the case where you want to add more than one Author to a Book. That goes beyond the scope of this tutorial because it requires javascript (or a multi-page workflow).

Step: Commit your Work

git add .
git commit -m"Handling multivalued fields"

Next Step

Return to the Dive into Hydra tutorial.