英文:
Springboot obtaining object from thymeleaf option
问题
以下是翻译的内容：
我正在尝试使用Spring Boot和Thymeleaf创建一个新的Product对象。我将一个包含Category的List<Category>传递给Thymeleaf，并在选项选择框中显示它们，以便在创建对象时进行选择。问题是对象被创建了，但是Category为null，我不确定为什么。
这是我的Product类的实例变量：
@Document(collection = "products")
public class Product {
@Id
private String id;
private String name, description;
private double price;
private Binary image;
private Category category;
private ProductStatus status;
public Product() {
}
}
它有一个Category的实例变量：
@Document(collection = "categories")
public class Category {
@Id
private String id;
private String name, description;
public Category() {
}
}
这是创建Product选项的Thymeleaf代码，其中包含Category：
<form method="post" th:action="@{/products/add}" th:object="${product}" enctype="multipart/form-data">
以及控制器部分：
m.addObject("product", new Product());
<div class="widget-content widget-content-area">
<div class="input-group mb-6">
<div class="input-group-prepend">
<span class="input-group-text">Product Category</span>
</div>
<select th:field="*{category}">
<option th:each="cat : ${categories}"
th:value="${cat}"
th:text="${cat.getName()}">Wireframe</option>
</select>
</div>
</div>
我有一个执行在product/add的POST按钮，这是用于它的REST API端点：
@RequestMapping(value = {"/products/add"}, method = RequestMethod.POST)
public ModelAndView addProduct(ModelAndView m, @Valid Product product, MultipartFile file) throws IOException {
User admin = userRepository.findByEmail(SecurityContextHolder.getContext().getAuthentication().getPrincipal().toString());
System.out.println("cat: " + product.getCategory().getName());
它接受一个@Valid的Product product，在我尝试打印所选的Category名称时，我得到一个NPE。我正在尝试从选项th:value="${cat}"中获取所选的Category，但是它不起作用。
英文:
So I am trying to create a new Product object with Springboot and Thymeleaf. I am passing in a List<Category> of categories into thymeleaf and displaying them in a option selection to be selected when the object is created. The issue is that the object is being created but the category is null and I am not sure why.
This is my products instance variables
public class Product {
@Id
private String id;
private String name, description;
private double price;
private Binary image;
private Category category;
private ProductStatus status;
public Product() {
}
It has a instance variable for Category.
@Document(collection = "categories")
public class Category {
@Id
private String id;
private String name, description;
public Category() {
}
This is the thymeleaf code for the creation of the Product option where category is held.
<form method="post" th:action="@{/products/add}" th:object="${product}" enctype="multipart/form-data">
and the controller
m.addObject("product", new Product());
<div class="input-group mb-6">
<div class="input-group-prepend">
<span class="input-group-text">Product Category</span>
</div>
<select th:field="*{category}">
<option th:each="cat : ${categories}"
th:value="${cat}"
th:text="${cat.getName()}">Wireframe</option>
</select>
</div>
</div>
I have a POST button that executes in the product/add
this is the rest API end point for it
@RequestMapping(value = {"/products/add"}, method = RequestMethod.POST)
public ModelAndView addProduct(ModelAndView m, @Valid Product product, MultipartFile file) throws IOException {
User admin = userRepository.findByEmail(SecurityContextHolder.getContext().getAuthentication().getPrincipal().toString());
System.out.println("cat: " + product.getCategory().getName());
It takes in a @Valid Product product
when I try to print out the category name which i selected I get an NPE.
I am trying to obtain the category selected from the option th:value="${cat}"
but it is not working.
答案1
得分: 1
将th:value="${cat}"更改为th:value="${cat.id}"，在<option>中进行修改。原因是您正在分配th:value="${cat}"中类别对象的引用值，该值将不再存在于内存中。由于Spring将自动将ID转换为相应的对象，我们只需将ID分配给值。category=1将被转换为具有id=1的new Category()。
英文:
Short answer. Change th:value="${cat}" to th:value="${cat.id}" in <option>. The reason is you are assigning the reference value of category object in th:value="${cat}" which will no longer exists in memory. Since spring will automatically convert the id to respective object, we just have to assign id to value. category=1 will be converted to new Category() with id=1
答案2
得分: 0
你需要将对象添加到模型和视图中：
modelAndView.getModelMap().addAttribute("dto", dto);
然后在Thymeleaf的部分中获取它，例如：
<form th:action="@{/url}" th:object="${dto}" th:method="post">
<input type="date" th:field="${dto.date}">
</form>
然后你可以在/url端点接收填充好的对象：
@Valid DtoClass dtoClass
英文:
You need to add the object to the model and view:
modelAndView.getModelMap().addAttribute("dto", dto);
and get it in the thymeleaf side, for example:
<form th:action="@{/url}" th:object="${dto}" th:method="post">
<input type="date" th:field="${dto.date}">
Then you can recieve the filled object in the /url endpoint with:
@Valid DtoClass dtoClass
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论