Question

我使用嵌套实体向我的端点发送请求。但是当我用Parent解析请求体时，getChild总是返回null。

我的实体：

@Entity
public class Parent {

    @Id
    @GenericGenerator(name = "uuid-gen", strategy = "uuid2")
    @GeneratedValue(generator = "uuid-gen")
    @Type(type = "pg-uuid")
    private UUID id;

    @Column(nullable = false)
    private String name;

    @JsonBackReference(value="child")
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(foreignKey = @ForeignKey(name = "child_id"))
    private Child child;

    public Parent() {
    }

    public Card(UUID id, String name, Child child) {
        this.id = id;
        this.name = name;
        this.child = child;
    }

    public UUID getId() {
        return id;
    }

    public void setId(UUID id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setChild(Child child) {
        this.child = child;
    }

    public Child getChild() {
        return child;
    }

}

@Entity
public class Child {

    @Id
    @GenericGenerator(name = "uuid-gen", strategy = "uuid2")
    @GeneratedValue(generator = "uuid-gen")
    @Type(type = "pg-uuid")
    private UUID id;

    @Column(nullable = false)
    private String name;

    @JsonManagedReference(value="child")
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "parent", cascade = CascadeType.ALL)
    private List<Parent> parents;

    public Child() {
    }

    public Child(UUID id, String name, List<Parent> parents) {
        this.id = id;
        this.name = name;
        this.parents = parents;
    }

    public UUID getId() {
        return id;
    }

    public void setId(UUID id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Parent> getParents() {
        return parents;
    }

    public void setParents(List<Parent> parents) {
        this.parents = parents;
    }

}

我向/parents发出POST请求以创建父级，但我有一个尚未创建的子级，但我想一起创建它们并链接它们。

我发送的请求：

{
    "name": "Your name",
    "child" : {
         "name": "Child name"
    }
}

我期待的是什么：

{
    "id": "uuid",
    "name": "Your name",
    "child" : {
         "id": "childuuid"
         "name": "Child name"
    }
}

但我得到的是：

{
    "id": "uuid",
    "name": "Your name"
}

我的控制器：

@RequestMapping(value = "/parents", method = RequestMethod.POST)
    public Card createParent(
            @RequestBody Parent parent
    ) {
        Child child = parent.getChild(); // always null :(
        ....do something to create both child and parent 

        return parentService.create(parent);
    }

Answer 1

点击此帖：JsonManagedReference vs JsonBackReference

JsonBackReference阻止项被序列化，这是为了避免在序列化时无限递归。

Parent1 - ＆gt;孩子 - ＆gt; Child1 - ＆gt;父母 - ＆gt; Parent1 - ＆gt;孩子 - ＆gt; Child1

您可以反转JsonManagedReference，JsonBackReference关系，但在序列化Parent时将忽略parents字段。

我发现DTO运行良好，它们将您的传输格式和数据库格式分离，这非常有用。

在spring中从请求json创建嵌套实体

1 个答案: