@RequestMapping(value = "/purchase/{id}", produces = "text/html")
  public String purchase(@PathVariable("id") Integer id, Model uiModel) {
    uiModel.asMap().clear();

    uiModel.addAttribute("proposal", Proposal.findProposal(id));
    uiModel.addAttribute("proposal_id", id);

    uiModel.addAttribute("purchaseRequest", new PurchaseRequest());
    return "user/purchaserequest/purchase";
  }