JavaSpringMVC/JSTL/JPA集成：使用SpringMVC更新现有子元素并向父实体添加新的子元素

Question

我是SpringMVC和JPA的新手。我正在用这些框架做一个学生项目。在这个项目中，我想实现一个JSP来更新现有的子元素，并向父实体添加新的子元素。 我的解决方案奏效了。但我认为应该有一种更优雅或“标准”的方式来做到这一点。以下是我的代码：

JPA实体

@Entity
public class Parent {
    @Id
    @GeneratedValue
    private Integer id;
    private String name;
    @OneToMany(mappedBy = "parent", fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true)
    private Set<Child> children = new HashSet<Child>();
    // constructors, getters and setters
}

@Entity
public class Child{
    @Id
    @GeneratedValue
    private Integer id;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "parentId")
    private Parent parent;

    private String name;
    // constructor getter and setter
}

命令名类

public class CommandName {
    private Parent parent;
    private List<Child> existingChildren = new ArrayList<Child>();
    private List<Child> newChildren = new ArrayList<Child>();

    private static final int MAX_NUM_NEW_CHILDREN = 3;

    public CommandName(Parent parent) {
          this.parent = parent;
          this.existingChildren.addAll(parent.getChildren());
          for (int i = 0; i < MAX_NUM_NEW_CHILDREN; ++i) {
                newChildren.add(new Child());
          }
    } 
    // getters and setters
}

控制器类

@Controller
public class MyController {
    @Autowired
    private ParentRepository parentRepository;

    @RequestMapping(value = "/editParent/{parentID}", method = RequestMethod.GET)
    public String editParent(ModelMap model, @PathVariable("parentID") Integer parentID) {
        CommandName cn = new CommandName(parentRepository.findOne(parentID));
        model.addAttribute("cn", cn);
        return "edit";
    }

    @RequestMapping(value = "/saveParent", method = RequestMethod.POST)
    public String saveParent(CommandName cn, BindingResult bindingResult) {
        Parent parent = cn.Parent();
        List existChildren = cn.getExistingChildren();
        for (Child c : existChildren) {
            c.setParent(parent);
        }
        List newChildren = cn.getNewChildren();
        for (Child c: newChildren) {
            c.setParent(parent);
        }
        parent.getChildren().addAll(existChildren);
        parent.getChildren().addAll(newChildren);
        parentRepository.save(parent);
        return "redirect:/view";
    }
}

编辑中的表单。jsp

<f:form role="form" action="/saveParent" commandName="cn">

<f:hidden path="parent.id"/>
<f:label path="parent.name">Parent Name</f:label>

<f:input type="text" path="parent.name"/>

<label>Children</label>
<c:forEach items="${cn.existingChildren}" var="child" varStatus="status">
    <f:hidden path="child.id"/>
    <f:input type="text" path="existingChildren[${status.index}].name"/>
</c:forEach>

<c:forEach items="${cn.newChildren}" var="child" varStatus="status">
    <f:input type="text" path="newChildren[${status.index}].name"/>
</c:forEach>

<button type="submit">Submit</button>
</f:form>

这些代码集起作用了：父级和现有子级被更新。新的孩子们被创造出来了。但是在saveParent（）方法中，我必须执行以下操作来重新链接所有内容。有没有更好的方法（更好的commandName类，更好的jsp表单？）非常感谢

List existChildren = cn.getExistingChildren();
for (Child c : existChildren) {
    c.setParent(parent);
}

Answer 1

正如在你的问题中，你没有更新的父母，也没有必要去嘲笑现有的孩子。。只添加新的孩子。。所以 将/saveParent帖子更改为：

@RequestMapping(value = "/saveParent", method = RequestMethod.POST)
    public String saveParent(CommandName cn, BindingResult bindingResult) {
        Parent parent = cn.Parent();
        List existChildren = cn.getExistingChildren();
        for (Child c : existChildren) {
            c.setParent(parent);
        }
        List newChildren = cn.getNewChildren();
        for (Child c: newChildren) {
            c.setParent(parent);
        }
        parent.getChildren().addAll(existChildren);
        parent.getChildren().addAll(newChildren);
        parentRepository.save(parent);
        return "redirect:/view";
    }

致：

@RequestMapping(value = "/saveParent", method = RequestMethod.POST)
    public String saveParent(CommandName cn, BindingResult bindingResult) {
        Parent parent = cn.getParent();
        if(parent.getId()!=null)//if parent id is not null, then retrieve the parent from database. and update it.
            parent = parentRepository.findOne(cn.getParent().getId());
        for(Child c : cn.getNewChildren()){
            c.setParent(parent);
            parent.getChildren().add(c);
        }
        parentRepository.save(parent);
        return "redirect:/view";
    }