Question

Suppose I have Post HABTM Tag and I am using mass asignment through nested attributes.

I have this in Post model:

accepts_nested_attributes_for :posts_tags, \
                              :reject_if => proc { |attrs| attrs.tag_id.blank? }

I have this in Post controller:

def new
  @post = Post.new
  3.times { @post.posts_tags.build }
end

def create
  @post = Post.new(params[:post])
  @post.save
end

And this in Post form:

<%= f.fields_for :tags do |tg| %>
  <%= tg.label :tag_id %>
  <%= tg.select :tag_id .... %>
<% end %>

Everything works just perfectly and with minimal code. The Post gets accociated with Tags that were selected.

And now: What if I want the users to select at least one Tag for their Post. How can I invalidate Post that has no Tag selected? What would be the most elegant solution?

Answer 1

Add validates_presence_of :tags in Post model to force the user to select the tag.