task.rb

def self.unanswered_with_max(user, task)
    joins("LEFT OUTER JOIN answers a ON a.input_id=inputs.id \
    AND a.user_id=#{user.id}")
    .joins('LEFT OUTER JOIN input_allocations ON input_allocations.input_id='\
    'inputs.id AND input_allocations.expires_at>\'' + Time.now.to_s + '\'')
    .where('a.id IS NULL')
    .where(task_id: task.id)
    .group('inputs.id,input_allocations.input_id')
    .having('COUNT(input_allocations.input_id)+answers_count<?',
    task.max_answers)
  end