Get parent id in bidirectional sleep mapping

Question

I have a spring vacation application with two bidirectional objects (one-to-many, many to one). To overcome the nested problems, @ JsonManagedReference / @ JsonBackReference was used for relations between child and child relations.

It is the following:

@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; } } 

This works great when retrieving the Parent element, then the child set is selected and displayed as a json array.

However, in the child element there is no reference to the parent element due to the use of jsonbackreferance.

I would like to either get the parent attached to the children in the json response, or at least get the parent id when requesting a single child via rest.

All reviews will be sent :)

Answer 1

I had a similar problem and solved it with a specialized serializer / deserializer

This is how I handle it (please adapt it to your own code):

Childseerializer

 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(); } } 

Child

 @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; } } 

Parent

 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; } } 

My testing method:

 @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(); } } 

Final result:

 {"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"}} 

A sad annotation is important, but does not always allow you to get what you need, and therefore you need to do it "on your own"

I hope this can be useful