Sinatra and Datamapper - inserting data to a one to many relationship table

Question

I have the following. Each article has a title and a body and also up to three urls. I would want to store the urls in a different table. Therefore in my form, i've a field for the urls. However they are not working, only the article fields get entered into the database. how should i specify them? Could any kind soul help me out with this?

class Article
  include DataMapper::Resource

  property :id,     Serial
  property :title,  String
  property :body,   Text

  has n, :urls, through => Resource
end

class Url
  include DataMapper::Resource

  property :id,     Serial
  property :url_01,    String
  property :url_02,    String
  property :url_03,    String

  belongs_to :article
end

post '/create' do
  @article = Article.new(params[:article])
  if @article.save
    redirect "/articles"
  else
    redirect "/articles/new"
  end
end

--------------------------------------
<form action="/create" method="post">
  <p>
    <label>Article Title</label>
    <input type="text" name="article[title]">
  </p>
  <p>
    <label>Article Body</label>
    <input type="text" name="article[body]">
  </p>
  <p>
    <label>Url</label>
    <input type="text" name="article[url_01]">
  </p>

  <p>
    <input type="submit">
  </p>

Answer 1

I believe that

, through => Resource

is only needed if you are doing a many-to-many relationship. A one-to-many, which I think is what you want, does not require that. Check out the post and comment relationship shown on the associations page.

EDIT for comment:

If I were you, I would name my form fields normally and construct the database object manually, for example:

<form action="/create" method="post">
  <p>
    <label>Article Title</label>
    <input type="text" name="title">
  </p>
  <p>
    <label>Article Body</label>
    <input type="text" name="body">
  </p>
  <p>
    <label>Url</label>
    <input type="text" name="url">
  </p>

  <p>
    <input type="submit">
  </p>

and then:

post '/create' do
  @article = Article.new(
      :title      => params[:title],
      :body       => params[:body]
  )
  @url = url.new(
      url_01 => params[:url]
  )
  @article.url = @url

  if @article.save
    redirect "/articles"
  else
    redirect "/articles/new"
  end
end