Creating nested entities in spring from request json

Question

I send a request to my endpoint with a nested entity. But getChild always returns null when I parse the requestbody with Parent.

My Entities:

@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;
    }

}

I make a POST request to /parents to create the parent but I have a child which is not created yet but I want to create them together and link them.

The request I send:

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

What I would expect:

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

But what I get is:

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

My Controller:

@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);
    }

@Steve Updated it there. Sorry made typo when making the example more generic. — PLZhalp, Mar 12 '18 at 22:13

score 0 · Accepted Answer · answered Mar 12 '18 at 22:20

Check out this post here: JsonManagedReference vs JsonBackReference

JsonBackReference prevents the item from being serialized, this is to avoid infinite recursion while serializing.

Parent1 -> child -> Child1 -> parents -> Parent1 -> child -> Child1

You can reverse the JsonManagedReference, JsonBackReference relationship but then the parents field will be ignored when you serialize Parent.

I find that DTOs work well, they decouple your transport format and database format which can be very useful.

Reversing the relationship was exactly what was needed. Thank you. One thing I had to remove `JsonManagedReference` entirely to get it to work but the idea was correct. Marking as the answer. — PLZhalp, Mar 12 '18 at 22:51

Creating nested entities in spring from request json

1 Answers1