Question

我有一个弹簧休息应用程序，它有两个带有双向关系的实体（一对多，多对一）。为了克服嵌套的提取问题，@ JsonManagedReference / @ JsonBackReference已用于实体之间的perent / child关系。

这些人看起来像这样：

@Entity
@Table(name = "Parent")
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Parent implements java.io.Serializable {

    private Integer id;
    private List<Child> childList;

    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "ID", unique = true, nullable = false)
    public Integer getId() {
        return this.id;
    }
    public void setId(Integer id) {
        this.id = id;
    }

    @OneToMany(mappedBy = "parent", fetch = FetchType.LAZY)
    @JsonManagedReference
    public List<Child> getChildList() {
        return childList;
    }

    public void setChildListe(List<Child> childListe) {
            this.childList = childList;
        }

    }


@Entity
@Table(name = "Child")
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Child implements java.io.Serializable {


    private Integer id;
    private Parent parent;

    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "ID", unique = true, nullable = false)
    public Integer getId() {
        return this.id;
    }

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

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ParentID")
    @JsonBackReference
    public Parent getParent() {
        return parent;
    }

    public void setParent(Parent parent) {
        this.parent = parent;
    }


}

这在获取Parent元素时工作正常，然后将childset同时提取并显示为json数组。

但是，由于使用了jsonbackreferance，子元素中没有父元素的引用。

我希望在json响应中获取附加到child-elemens的父对象，或者在通过休息请求单个子元素时至少获取父ID。

所有反馈都将受到关注：）

Answer 1

我有一个类似的问题，我通过使用自定义序列化器/反序列化器解决了它

这就是我的处理方式（请根据您自己的代码进行调整）：

<强> ChildSerializer

public class ChildSerializer extends StdSerializer<Child> {

    private static final long serialVersionUID = -265706839304575646L;
    public ChildSerializer(Class<Child> t) {
        super(t);
    }
    public ChildSerializer() {
        this(null);
    }
    @Override
    public void serialize(Child child, JsonGenerator jg, SerializerProvider sp)
            throws IOException, JsonGenerationException {

        jg.writeStartObject();
        jg.writeStringField("name", child.getName());
        jg.writeStringField("surname", child.getSurname());
        Parent parent = child.getParent();
        jg.writeObjectFieldStart("parent");
        jg.writeStringField("name", parent.getName());
        jg.writeStringField("surname", parent.getSurname());
        jg.writeEndObject();
    }
}

儿童

@JsonSerialize(using = ChildSerializer.class) public class Child implements Serializable { private static final long serialVersionUID = 7902561110976676934L; private String name; private String surname; private Parent parent; public Child(String name, String surname, Parent parent) { this(name, surname); this.parent = parent; } public Child(String name, String surname) { this(); this.name = name; this.surname = surname; } public Child() { super(); } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSurname() { return surname; } public void setSurname(String surname) { this.surname = surname; } public Parent getParent() { return parent; } public void setParent(Parent parent) { this.parent = parent; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((name == null) ? 0 : name.hashCode()); result = prime * result + ((parent == null) ? 0 : parent.hashCode()); result = prime * result + ((surname == null) ? 0 : surname.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Child other = (Child) obj; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; if (parent == null) { if (other.parent != null) return false; } else if (!parent.equals(other.parent)) return false; if (surname == null) { if (other.surname != null) return false; } else if (!surname.equals(other.surname)) return false; return true; } }

<强>父

public class Parent implements Serializable { private static final long serialVersionUID = -5604725691780073247L; private String name; private String surname; private List<Child> childs; public Parent(String name, String surname) { this(); this.name = name; this.surname = surname; } public Parent(String name, String surname, List<Child> childs) { this(name, surname); this.childs = childs; } public Parent() { super(); childs = new ArrayList<Child>(); } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSurname() { return surname; } public void setSurname(String surname) { this.surname = surname; } public void addChild( Child child ) { if( !childs.contains(child) ) { child.setParent(this); childs.add(child); } } public List<Child> getChilds() { return childs; } public void setChilds(List<Child> childs) { this.childs = childs; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((childs == null) ? 0 : childs.hashCode()); result = prime * result + ((name == null) ? 0 : name.hashCode()); result = prime * result + ((surname == null) ? 0 : surname.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Parent other = (Parent) obj; if (childs == null) { if (other.childs != null) return false; } else if (!childs.equals(other.childs)) return false; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; if (surname == null) { if (other.surname != null) return false; } else if (!surname.equals(other.surname)) return false; return true; } }

我的测试方法：

@Test public void testJson() { try { Parent p = new Parent(UUID.randomUUID().toString(), UUID.randomUUID().toString()); for (int i = 0; i < 10; i++) { p.addChild(new Child(UUID.randomUUID().toString(), UUID.randomUUID().toString())); } ObjectMapper om = new ObjectMapper(); String childJson = om.writeValueAsString(p.getChilds().get(0)); System.out.println(childJson); } catch (Exception e) { e.printStackTrace(); } }

最终输出是：

{"name":"b86eab86-9858-4536-9c5c-d44d22810fc1","surname":"9a6249f0-58df-44e5-a1b9-31fbad6e9f49","parent":{"name":"74b0cd97-64a1-4547-ab22-4e4eedd0759b","surname":"a33c79f3-6f26-478b-9e24-7df96b3b1f68"}}

可悲的是，注释是强大的，但并不总是它们允许你获得你需要的东西，所以你必须自己做＃34;

我希望这可以是有用的

在双向hibernate映射中获取parent-id

1 个答案: