将对象从th:each循环发送到控制器

Question

我有窗体和相应的控制器，对象列表被传递给它们。

实体类：

    @Entity
    public class Entity1
       @Id
       @Column(name="id")
       @GeneratedValue(strategy = GenerationType.IDENTITY)
       private long id;
    
       @ManyToOne(cascade = CascadeType.PERSIST)
       @JoinColumn(name = "entity2_id")
       private Entity2 entity2Field; 
    
    @Entity
    public class Entity2
    
       @Id
       @Column(name="id")
       @GeneratedValue(strategy = GenerationType.IDENTITY)
       private long id;
    
       @Column(name="name")
       private String name; 

控制器：

    @GetMapping(value="/create")
    puplic String show(Model entity1Model, Model entity2Model){
        
        entity1Model.addAttribute("entity1", new Entity1());
        List<Entity2> list= entity2Repository.findAll();
        entity2Model.addAttribute("entity2list", list);
        return "form"
        }

    @PostMapping(value="/create/new")
    public String save(Entity1 entity1, @RequestParam(name="entity2list) String somevalue{
        Entity2 entity2= entity2Repository.findByName(somevalue);
        entity1.setEntity2Field(entity2)
        entity1Repository.save(entity1)
        return "redirect:/"  
    }

形式：

<form method="post" th:action="@{create/new}">
  <select class="form-control" name="entity2list">
    <option th:each="ent2:${entity2list} 
      th:value="${ent2.name} th:text="${ent2.name}>
  </select>
  <button type="submit"></button>
</form>

我假设表单中的百里叶th:each循环变量不能是th:object=${ent2}(因为如果我这样做，select form返回null)。而th:value="${ent2.name}返回字符串值。所以我不得不将@RequestParam(th:value)发送给“save”方法。但是在这种情况下，我必须对数据库进行额外的请求，以获取Entity2对象并将其设置为Entity1。

我怎样才能以某种方式获得实体对象，比如:

<form method="post" th:action="@{create/new}">
  <select class="form-control">
    <option th:each="ent2:${entity2list} 
      th:object="${ent2} th:text="${ent2.name}>
  </select>
  <button type="submit"></button>
</form>

并将（@ModelAttribute（“ent2”）Entity2 ent2而不是@RequestParam）发送到“save”方法，以避免对数据库的冗余请求？

Answer 1

我已经解决了问题 th：field=“*{entity2Field} 的工作方式类似于 setter https://www.thymeleaf.org/doc/tutorials/3.0/thymeleafspring.html#creating-a-form

<form method="post" th:action="@{create/new}" th:object="${entity1}">
      <select class="form-control" th:field="*{entity2Field}>
        <option th:each="ent2:${entity2list} 
          th:value="${ent2} th:text="${ent2.name}></option>
      </select>
      <button type="submit"></button>
</form>