How to make a relationship between ticket and current_user.

At first , you should write belongs_to :user in ticket model.
And use merge! method to make a relationship between ticket and current_user in create action of tickets_controller.

  def create
    @ticket = @project.tickets.build(params[:ticket].merge!(:user => current_user))
    if @ticket.save
      flash[:notice] = "Ticket has been created."
      redirect_to [@project,@ticket]
    else
      flash[:alert] = "Ticket has not been created."
      render :action => "new"
    end
  end