问题描述
您好，我对@ModelAttribute批注有疑问.据我了解，我们在方法参数中使用@ModelAttribute从模型中获取数据.但是，很难清楚地了解何时以及如何使用它.(代码示例摘自Spring in Action 5书)为什么在这种情况下，在以下 public String processOrder()方法中的代码中，我们不对 @有效订单
Hello I have question about @ModelAttribute annotation. As i understand, we use @ModelAttribute in method arguments to get data from the model. But it's quite hard to understand clearly when and how its used.(Code samples are from Spring in Action 5 book)Why in this case in the code below in public String processOrder() method we do not use @ModelAttribute annotation on @Valid Order order
@Controller
@RequestMapping("/orders")
@SessionAttributes("order")
public class OrderController {
private OrderRepository orderRepo;
public OrderController(OrderRepository orderRepo) {
this.orderRepo = orderRepo;
}
@GetMapping("/current")
public String orderForm(@AuthenticationPrincipal User user,
@ModelAttribute Order order) {
if (order.getDeliveryName() == null) {
order.setDeliveryName(user.getFullname());
}
//following conditions
return "orderForm";
}
@PostMapping
public String processOrder(@Valid Order order, Errors errors, // <<< Here
SessionStatus sessionStatus,
@AuthenticationPrincipal User user) {
if (errors.hasErrors()) {
return "orderForm";
}
order.setUser(user);
orderRepo.save(order);
sessionStatus.setComplete();
return "redirect:/";
}
}
但在这种情况下，在@Valid Taco taco上使用方法 processDesign()上的DesignTacoController类@ModelAttribute:
but in this case, DesignTacoController class, @ModelAttribute on a method processDesign() is used on @Valid Taco taco:
@Slf4j
@Controller
@RequestMapping("/design")
public class DesignTacoController {
@PostMapping
public String processDesign(@Valid @ModelAttribute("design") Taco design, // <<< Here
Errors errors, Model model) {
if (errors.hasErrors()) {
return "design";
}
// Save the taco design...
// We'll do this in chapter 3
log.info("Processing design: " + design);
return "redirect:/orders/current";
}
然后在下一章中，作者从同一DesignTacoController类的 processDesign()方法中删除@ModelAttribute.
And then in the next chapter author removes @ModelAttribute from processDesign() method from the same DesignTacoController class.
@Controller
@RequestMapping("/design")
@SessionAttributes("order")
@Slf4j
public class DesignTacoController {
@ModelAttribute(name = "order")
public Order order() {
return new Order();
}
@ModelAttribute(name = "design")
public Taco design() {
return new Taco();
}
@PostMapping
public String processDesign(
@Valid Taco taco, Errors errors, // <<< Here
@ModelAttribute Order order) {
log.info(" --- Saving taco");
if (errors.hasErrors()) {
return "design";
}
Taco saved = tacoRepo.save(taco);
order.addDesign(saved);
return "redirect:/orders/current";
}
在此代码段中(来自上面的代码):
And in this code snippet(from the code above):
@PostMapping
public String processDesign(
@Valid Taco taco, Errors errors, // <<< Here
@ModelAttribute Order order) {
....
}
书中的
引用:"Order参数用@ModelAttribute注释，以指示其值应来自模型，并且Spring MVC不应尝试绑定向其请求参数."我不明白作者在这里的意思，因为在所有教程中都说@ModelAttribute用作方法参数时，它将请求参数绑定到它.将表单数据与POJO bean绑定，然后使用来自提交表单的数据填充模型属性.
quote from book: "The Order parameter is annotated with @ModelAttribute to indicate that itsvalue should come from the model and that Spring MVC shouldn’t attempt to bindrequest parameters to it."This I don't understand what author meant here, because in all tutorials it is said that when @ModelAttribute is used as a method arguments,it binds request parameters to it. Binds the form data with a POJO bean, model attribute is populated with data from a form submitted.
推荐答案
我也不清楚.
在这里，我们需要指定模型属性的名称.因为我们认为我们将其命名为"design"而不是"taco".
Here we need specify the name if the model attribute.Because in our view we assume it is named "design" and not "taco".
@PostMapping
public String processDesign(@Valid @ModelAttribute("design") Taco design, Errors errors) {
如果我们将Taco类重命名为Design ...如果模型属性，我们不需要指定名称.它将从类的简单名称推导出来.com.example.Design-> "design"
If we rename the Taco class to Design ...We don't need to specify the name if the model attribute.It will be deduced from the simple name of the class.com.example.Design -> "design"
@PostMapping
public String processDesign(@Valid Design design, Errors errors) {
这篇关于我们何时必须使用@ModelAttribute及其工作方式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！