title: Rails 4 - Custom validation method not being called
body: <p>I have a validation method that should validate whether an user is part of a team. If it is not part of the team it should add an error and thus failing to save the record.</p>
  
  <p>This is the current method that is inside the model:</p>
  
  <pre><code>def assignee_must_be_part_of_team
    unless assignee_id.blank?
      team = Team.find(self.team_id)
      errors.add(:team, 'Equipe não existe') unless team
      user = team.users.find(self.assignee_id)
      errors.add(:assignee_id, 'Responsável não faz parte da equipe') unless user
    end
  end
  </code></pre>
  
  <p>And I am registering it in my model with this:</p>
  
  <pre><code>validate :assignee_must_be_part_of_team, on: :save
  </code></pre>
  
  <p>However, this method is not being even called when I save a new record! I even tried to add some logs to it but nothing happens and the record is being saved anyway.</p>
  
  <p>Am I missing anything here?</p>