Passing an instance of one object to another

rubyonrails-talk
1

Hello,

I'm working on my first Rails app. It's a redesign for a magazine site. I have a class for the articles and a class for issues. I've set up a has_many/belongs_to relationship between the two so that every article belongs to a particular issue.

Now I'd like to set it up so that a new article cannot be added UNLESS you have already chosen the issue that it is to be added to. I'd like to set something up like "selected_issue.articles.build(params[:article])" but I don't know how to create an action/method that would allow me to set the selected_issue variable and then pass that into the create method on the article controller.

Could someone lend some assistance here?

Thanks.

2

you got it right. you can call @issue.articles.create( params[:article] ) to get a new article that is already saved and associated with the issue. you can also do @issue.articles.build( params[:article] ) if you want to get a new article object but not save it yet.

see here: http://api.rubyonrails.com/classes/ActiveRecord/Associations/ClassMethods.html#M000642

3

A common way to do this is for your "create article" form to have a select field for issue_id that allows the user to select from available issues.

In your view:

   <% form_for :article do |f| %>       <% select :issue_id, Issue.find(:all).collect {|p| [ p.name, p.id ] } %>       ...    <% end %>

Then in your controller,

   @article = new Article(params[:article])    if @article.save        ...blah blah

This will automatically assign the article to the selected issue.

If you want to ensure that the article is linked to a valid issue, add to your model:

   class Article < ActiveRecord::Base      belongs_to :issue      validates_presence_of :issue    end