Question

When using the form_for helper with an html.erb page, alot of the work is abstracted for you, so something like

f.label :book

gets turned into an html label. I want to fill in a text field with a string, so that I can take the values associated with several symbols, form them into a string, and put that string into the :value key.

<%= form_for(@backpack) do |f| %>
  <ul>
    <% @backpack.errors.full_messages.each do |error| %>
        <li><%= error %></li>
    <% end %>
  </ul>
  <p>
    <%= f.label :calculator %><br/>
    <%= f.text_field :calculator %>
  </p>
  <p>
    <%= f.label :lunchbox %><br/>
    <%= f.text_field :lunchbox %>
  </p>
    <%= f.label :books %><br/>
  </p>
    <%= f.fields_for :books do |g| %>
      <p>
        <%= g.text_field :book, :value => MY_STRING %>
      </p>
    <% end %>
  </p>
  <p>
    <%= f.submit %>
  </p>
<% end %>

MY_STRING = :title by :author

So, if I left g.text_field alone with :book, it would automatically fill in the string associated with that symbol. How can I implement that in my custom way? How exactly do symbols reference the actual data in my nested form?

I should also mention I have the

accepts_nested_attributes_for :books

attribute in my backpack controller, so I have access to the second model/database

Answer 1

A symbol is just a symbol. No direct connection to the object. But you can use the book object attached to the form builder to create a string describing the book:

<%= g.text_field :book, :value => "#{g.object.title} by #{g.object.author}" %>

Even better, you can write a helper to handle this for you:

# in backpacks_helper.rb
def book_title(book)
  "#{book.title} by #{book.author}"
end

And use it like so:

<%= g.text_field :book, :value => book_title(g.object) %>