Hibernate Cascading problems with OneToMany

Question

I'm trying to understand how to properly annotate classes to get cascading to work.

Here is a simple parent/children scenario.

Child:

@Entity
@Table(name = "testChild")
public class testChild implements Serializable {
    @Id
    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "uuid2")
    @Column(name = "uuid", unique = true, nullable = false)
    @JsonProperty
    private String uuid;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name="parent_uuid", nullable=false)
    @Cascade(value={CascadeType.ALL})
    @JsonIgnore
    private testParent parent;

    @Column(name = "name")
    @JsonProperty
    private String name;    

    public testChild (testParent parent, String name) {
        this.uuid = UUID.randomUUID().toString();
        this.name = name;
        this.parent = parent;
    }

    public String getUuid() {
        return this.uuid;
    }

    public void setUuid(String uuid) {
        this.uuid = uuid;
    }

    public String getName() {
        return this.name;
    }

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

    public testParent getParent () {
        return this.parent;
    }

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

Parent:

    @Entity
@Table(name = "testParent")
public class testParent implements Serializable {
    @Id
    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "uuid2")
    @Column(name = "uuid", unique = true, nullable = false)
    @JsonProperty
    private String uuid;        // This is the figure uuid:<number> 

    @Column(name = "name")
    @JsonProperty
    private String name;    

    @Column(name = "children")
    @OneToMany(fetch = FetchType.EAGER, mappedBy = "parent", orphanRemoval=true, cascade = javax.persistence.CascadeType.ALL)
    @Cascade({CascadeType.SAVE_UPDATE, CascadeType.DELETE})
    @JsonProperty
    private List <testChild> children;    

    public testParent (String name) {
        this.uuid = UUID.randomUUID().toString();
        this.name = name;
        this.children = new ArrayList<>();
    }

    public String getUuid() {
        return this.uuid;
    }

    public void setUuid(String uuid) {
        this.uuid = uuid;
    }

    public String getName() {
        return this.name;
    }

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

    public List <testChild> getChildren () {
        return this.children;
    }

    public void setChildren (List <testChild> children) {
        this.children = children;
    }

    public testChild addChild(String childname) {
        testChild c = new testChild(this, childname);
        this.children.add(c);
        return c;
    }
}

And the test code:

testParent p = new testParent("Dan");
sid = p.getUuid();

testChild c1 = p.addChild("Dan jr.");
testChild c2 = p.addChild("Dannielle");
session.save(p);

My problem is that it's resulting in an update to the (first) child instead of an insert:

DEBUG org.hibernate.SQL - insert into testParent (name, uuid) values (?, ?)
DEBUG org.hibernate.SQL - update testChild set name=?, parent_uuid=? where uuid=?

Of course this throws an error. I have tried quite a few combinations for Cascade in both the parent and child classes.

The only thing that does work is if I explicitly "session.save(object)" all the time. ie Create the parent - save, create child1 - save, create child2 - save, finally save the parent again.

I'd really like to know how to tell Hibernate to simply save everything from the top down.

Tried a lot of different suggestions from this site and others, but nothing seems to be working.

Answer 1

You have to explicitly use the setter for parent and child.

Here is what you have to do:

 testParent p = new testParent("Dan");

 testChild c1 = new testChild("Dan");
 testChild c2 = new testChild("Dannielle");

 c1.setParent(p);
 c2.setParent(p);

 p.getChildren().add(c1);
 p.getChildren().add(c2);
 session.save(p);

You've also probably mixed up the entity cascades. On your OneToMany side, ie testParent , you need to have CascadeType.ALL or include CascadeType.PERSIST. You want to say that whenever you want to 'insert' or 'update' or 'delete' a parent, please also do the same action on the children.

The save of the parent should cascade the save to its referenced children as well.

Answer 2

I have a partial answer. It fixes the problem, but I'm still a little confused. The problem has to do with using the generated ID's. I was also trying to set them manually and that I think was breaking the mappings between parent and child.

Here is some working code:

    try {
        testParent p = new testParent("Dan");
        sid = p.getUuid();

        testChild c1 = new testChild("Dan Jr.");
        testChild c2 = new testChild("Danielle");

        c1.setParent(p);
        c2.setParent(p);
        p.getChildren().add(c1);
        p.getChildren().add(c2);

        session.save(p);            
        tx.commit();

    } catch(Exception e) {
        tx.rollback();
        log.error("Exception occured. "+e.getMessage());
        assertTrue(false);
    }

But it only works when I do two things:

1. Remove the @GeneratedValue and @GenericGenerator annotations from the class definitions.
2. Make sure that my constructors manually create these id fields.

If I don't do that, then it seems that setUuid does not update the uuid field when persisted to the DB. The object gets the new id, but only the original generated ID is saved.

I wonder if this is the best way to do this.