title: Using CakePHP, save extra field (id, value, amount) HABTM tables
body: <p>Hello Everything is right?
  My problem is the following:</p>
  
  <p>I have 3 tables:</p>
  
  <pre><code>create table products (
      id int not null auto_increment primary key,
      name varchar(80) not null,
      mold varchar(80),
      amount int,
      value decimal(10,2),
      real_value decimal(10,2),
      created datetime,
      modified datetime,
      active boolean default 1
  );
  
  create table sales (
      id int not null auto_increment primary key,
      customer_id int not null,
      method_payment_id int not null,
      portions smallint(4),
      entry decimal(10,2),
      subtotal decimal(10,2),
      total decimal(10,2),
      debtor decimal(10,2), 
      expiration_date datetime,
      created datetime,
      modified datetime,
      active boolean default 1
  );
  
  create table products_sales (
      product_id int not null,
      sale_id int not null,
      amount smallint(4),
      value decimal(10,2)
  );
  </code></pre>
  
  <p>In <strong>products_sales</strong> (HABTM) I had to add two extra fields (<strong>amount</strong> and <strong>value</strong>), because the value of a product is unstable and the other is the quantity purchased by the customer.</p>
  
  <p>When I put in add() page:</p>
  
  <pre><code>  echo $this-&gt;form-&gt;input('Product');
  </code></pre>
  
  <p>CakePHP renders a , until then I understand.<br /><br />
  But my need is: the customer must choose the <strong>product</strong> and the <strong>amount</strong> of it, or even if it is, the <strong>product value</strong> is also <strong>sent</strong>, <strong>not only</strong> the id (anything, I create a page just to report the amount, after confirmation 'the sale').<br /></p>
  
  <p>Then: <br />
  <strong>1</strong> - How do I save the ID and value of the product at the same time? <br />
  <strong>2</strong> - I am using the tables / relationships the right way? <br />
  <strong>3</strong> - what better way to do this? <br /></p>
  
  <p><em>Sorry for my English.
  I hope you understand.</em></p>