gistfile1.rb

class Project < ActiveRecord::Base
  belongs_to :collection
  has_many :items

  attr_accessible :name, :description, :links
  attr_accessor :image

  serialize :links

  validates :name, uniqueness: { scope: :collection_id }, length: {minimum: 1, maximum: 20}, allow_blank: false
  validates :description, length: {minimum: 5, maximum: 200}, allow_blank: true

  def set_image
    self.image = self.items.first.image
  end
end

gistfile2.txt

[57] pry(main)> a.set_image
NoMethodError: undefined method `set_image' for #<Project:0x00000008272510>
from /home/jayml/.rvm/gems/ruby-2.0.0-p0/gems/activemodel-3.2.13/lib/active_model/attribute_methods.rb:407:in `method_missing'

[59] pry(main)> Project.set_image
NoMethodError: undefined method `set_image' for #<Class:0x0000000853acc0>
from /home/jayml/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/dynamic_matchers.rb:55:in `method_missing'