class Job < ActiveRecord::Base
  validates :title, presence: true
  validates :company, presence: true
  validates :url, presence: true

  has_many :position_type_joins
  has_many :position_types, through: :position_type_joins

  accepts_nested_attributes_for :position_types, :allow_destroy => true

end

class PositionType < ApplicationRecord

  has_many :position_type_joins
  has_many :jobs, through: :position_type_joins

end

class PositionTypeJoin < ApplicationRecord
  belongs_to :job
  belongs_to :position_type
end

+-------------------+----------------------+
|     Job title     |    Position Type     |
+-------------------+----------------------+
| Painter           | Contract, Part time  |
| Library Assistant | Part time, Volunteer |
+-------------------+----------------------+

index do
  column :code
  column 'Sales Agent' do |client|
    client.sales_agent.agent_name if !client.sales_agent.nil?
  end
end

index do
    column 'Position type' do |job|
    job.position_type.name if !job.position_type.name?
  end
end

undefined method `position_type'