Question

I’m trying to block my users from having more than 5 pages. My pages model looks like this:

class Page < ActiveRecord::Base
  belongs_to :user, :counter_cache => true
  has_friendly_id :name, :use_slug => true, :strip_non_ascii => true
  validates_uniqueness_of :name, :case_sensitive => false
  validates_presence_of :name
end

And I’ve added a column in the db which is incrementing and decrementing fine.

I just don’t know what I should put in my controller now to thrown an error and stop them from adding too many.

Thanks again

— Update —

This is what my user model now looks like:

class User < ActiveRecord::Base
  has_many :pages, :dependent => :destroy, :before_add => :enforce_page_limit
  # Include default devise modules. Others available are:
  # :token_authenticatable, :encryptable, :confirmable, :lockable, :timeoutable and :omniauthable
  validates_presence_of :name
  validates_uniqueness_of :name, :email, :case_sensitive => false

  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :name, :email, :password, :password_confirmation, :remember_me
  has_friendly_id :name, :use_slug => true, :strip_non_ascii => true

  private

    def enforce_page_limit
      if self.pages_count >= 1
        self.errors.add_to_base "Page limit reached, can't add another page"
        raise "User page limit reaching, preventing page from being added"
      end
    end  
end

Answer 1

You can use a :before_add callback on the User side of the User-Pages relationship. Check out the Association callbacks section of this page: http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

You’ll want to write the callback to check to see if there already are 5 pages related to the user, and if there is, raise an exception to block the Page from being related to the User.

UPDATE

Here’s an example of how you would set up the before_add callback.

In your User model:

class User < ActiveRecord::Base

  has_many :pages, :before_add => :enforce_page_limit

  private

  def enforce_page_limit
    if self.pages.count >= 5
      self.errors.add_to_base "Page limit reached, can't add another page"
      raise "User page limit reaching, preventing page from being added"
    end
  end 

end