Custom Association Options

When ActiveScaffold displays a dropdown on the form of records to associate with the current record (the one being edited or created), it has to decide which records should be present. The default behavior is to display “orphaned” (unassociated) records for :has_one and :has_many associations, and to display all records for :belongs_to and :has_and_belongs_to_many, sorted by to_label method, or whatever is defined in the column’s sort_by.

You may want to display all records every time, or you may want to impose extra conditions. The solution is to create a method called options_for_association_conditions in your controller’s helper file. This method accepts an AssociationReflection object and current record, and returns SQL conditions (in any of the common formats).

This method is used in association columns with :select form_ui too.

For example, let’s say that you have a UsersController, and that a User has_and_belongs_to_many Roles. Let’s say that you don’t want to show the Admin Role as an option, unless the current user is an Admin. You’ve already got validation set up, but you just don’t want the option in the list. Here’s what you could do:

module UsersHelper
  def options_for_association_conditions(association, record)
    if association.name == :role
      ['roles.id != ?', Role.find_by_name('admin').id] unless current_user.admin?
    else
      super
    end
  end
end

Remember that, since this method is a view helper, you can access all the associated controller and views associated methods and variables, including the params; given this, you can easily access the record being edited in the @record variable:

class UsersController < ApplicationController
  active_scaffold do |config|
    config.columns[:author].form_ui = :select
    config.columns[:author].update_columns = :book
    config.columns[:book].form_ui = :select
  end
end

module UsersHelper
  def options_for_association_conditions(association, record)
    if association.name == :book
      {'books.author_id' => record.author_id}
    else
      super
    end
  end
end

If you want to use scopes to get the associated records, you must override association_klass_scoped method in your controller’s helper file. This method gets the AssociationReflection object, association class (or selected class for polymorphic associations) and current record. You can invoke super wich return model class or relation, and you can invoke scope methods on it.

class User < ActiveRecord::Base
  scope :with_role, lambda { |role| where(:role => role) }
end

module UsersHelper
  def association_klass_scoped(association, klass, record)
    if association.name == :role
      super.with_role('admin')
    else
      super
    end
  end
end

The method used to display the label can be changed in column’s options, with :label_method key, passing a symbol with the method’s name to use. Options will be sorted by this method too, instead of to_label.

conf.columns[:role].options[:label_method] = :label_with_extra_data

If the column has a SQL sort defined, it will be used to sort the options instead of sorting by the defined label method.

conf.columns[:role].sort_by sql: ['roles.level', 'roles.name']

If sort_by SQL is not defined, the order can be changed overriding the method sorted_association_options_find

module UsersHelper
  def sorted_association_options_find(association, conditions = nil, record = nil)
    if association.name == :role
      super.sort_by { |role| [role.level, role.name] }
    else
      super
    end
  end
end