post 'add' => :task_create
post 'add/:project_id' => :task_create, as 'create_project_task'
form_tag create_project_task(project_id: project.id), method: :post do ...
end
def single_reservation_for_period
if Reservation.where("start BETWEEN #{start} AND #{finish} OR finish BETWEEN #{start} AND #{finish}").present?
errors.add(:reserved, 'Invalid period of time. Already reserved')
end
end