title: Drop down menu with value from another model
body: <p>I have products belonging to collections. A collection is just a name. Products have a collection_id.</p>
  
  <p>In my _form view that is used for creation and edition of products, i'd like to have a drop down menu with the name of all collection. </p>
  
  <p>Problem, it seems there is no select method affiliated to form.for and i am trying to use :</p>
  
  <blockquote>
    <p>select(method, choices, options = {},
    html_options = {})</p>
  </blockquote>
  
  <p>from the doc but i do not understand it. I must write a methode to create a form? What are the choices, and the 2 options? Two parameters should be enough to populate an &lt; option>
   tag.</p>
  
  <p>How can I have a drop down menu alowing me to assign a collection through collection name to my product?</p>