title: Rails 4.2.0- Validates Association Counts for has_many Relationship
body: <p>I search high and low and can't seem to come to find a proper solution for this simple problem.</p>
  
  <p>Essentially, I would like to validates the amount of association between two models. </p>
  
  <p>I read somewhere, and tried using something like,
  <code>validates :attachments, inclusion: { in: 20}</code>
  and failed. </p>
  
  <p>Out of frustration, I removed the code, and don't have anything to show for right now. But I'll add it back when I came across the same problem again.</p>
  
  <p>Thank you for lending your helping hand! = )</p>