1class Project < ActiveRecord::Base
  
2  has_and_belongs_to_many :users
  
3
  
4  validate :require_at_least_on_user,on: :update #
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5
  
6  validates :name, presence: true, length: { minimum: 1, maximum: 50 }, uniqueness: true
  
7
  
8  private
  
 9
  
10    def  require_at_least_on_user
  
11      if !users || users.size == 0  # size
  
12        errors[:users] = 'at least one user in the project'
  
13      end
  
14    end
  
15end