using a validation with has_many_through - ruby-on-rails

Question

I want to set up a validation so that people can't submit a post unless they click on a category for that post and also to make sure that they can chose only one of the categorys for that post so the post can have only one category. Here are the modles
class Categorization < ActiveRecord::Base
belongs_to :post
belongs_to :category
end
class Category < ActiveRecord::Base
has_many :categorizations
has_many :posts, :through => :categorizations
end
class Comment < ActiveRecord::Base
belongs_to :user
validates :content, presence: true,
length: { minimum: 5 }
end
class Post < ActiveRecord::Base
belongs_to :user
has_many :comments
has_many :categorizations
has_many :categories, :through => :categorizations
validates :title, :content, presence: true,
length: { minimum: 5, maximum: 140 }
end
also here is my form:
<%= form_for #post, :html => {:multipart => true} do |f| %>
<% if #post.errors.any? %>
<div id="error_explanation" class="animated tada">
<h2><%= pluralize(#post.errors.count, "error") %> prohibited this post from being saved:</h2>
<ul>
<% #post.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :title %><br>
<%= f.text_field :title %>
</div>
<div class="field">
<%= f.file_field :image %>
</div>
<div class="field">
<%= f.label :content %><br>
<%= f.text_area :content %>
</div>
<%= hidden_field_tag "post[category_ids][]", nil%>
<% Category.all.each do |category| %><br>
<%= check_box_tag "post[category_ids][]", category.id, #post.category_ids.include?(category.id), id: dom_id(category)%>
<%= label_tag dom_id(category), category.name %>
<% end %>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
</div>
do any of you know what I would need to put in to make my form come back with a message saying need to select category or can pick only one category?

Answer 1

We've done a similar thing with has_many :through
Validating On The Join Model
Our solution was to use accepts_nested_attributes_for, and validate on the join model. This could be seen as quite inefficient, but works well for us:
#app/models/message.rb
Class Message < ActiveRecord::Base
validates :title, :body,
:presence => { :message => "Needs A Value!" }
accepts_nested_attributes_for :message_subscribers, :allow_destroy => true
end
#app/models/message_subscriber.rb
Class MessageSubscriber < ActiveRecord::Base
#Validations
validates :subscriber_id,
:presence => { :message => "Your Message Needs Subscribers!" }
end
This returns an error if you don't have any subscriber_id's selected
Your Code
For you, I'd be tempted to do this:
class Categorization < ActiveRecord::Base
belongs_to :post
belongs_to :category
#Validation
validates :subscriber_id, :presence => { :message => "You need to select a category!" }
end
class Post < ActiveRecord::Base
belongs_to :user
has_many :comments
has_many :categorizations
has_many :categories, :through => :categorizations
#Validation
validates :title, :content, presence: true,
length: { minimum: 5, maximum: 140 }
end
I was going to include accepts_nested_attributes_for for you, but I realized it would be an inconvenient way to do something you're doing already. In light of this, I believe you may be best suited just performing the validations in your join model, however if it does not work, we'll add the accepts_nested_attributes_for functionality