实体管理器批量更新给出 org.hibernate.PersistentObjectException: detached entity传递给持久化

Question

I tried to follow this article because with batch updates I get unnecessary selects using merge:

for(int i = 0; i< elements.size(); i++){
    Query q = em.createQuery("select p from Parent p join fetch p.child c where p.id=:id", Parent.class);
    //parameter of :id from elements
    Parent p = q.getSingleResult();
    p.setName("aname"); //for simplicity just the name member
    myList.add(p);
}

utx = com.arjuna.ats.jta.UserTransaction.userTransaction();
utx.begin();
em.joinTransaction();

for(int i = 0; i< myList.size(); i++){
    if (i > 0 && i % Common.BATCH_SIZE == 0) { //BATCH_SIZE=50
        em.flush();
        em.clear();
    }
    Parent myObject = myList.get(i);
    em.merge(myObject);
}
utx.commit();

This is my Entity definition:

@Entity
@Table(name = "myparenttable", schema = "myschema", catalog = "mydb")
@JsonIgnoreProperties(ignoreUnknown = true)
public class Parent implements Serializable {
    private Integer id_parent;
    private String name;

    @JsonManagedReference
    @JsonInclude(JsonInclude.Include.NON_NULL)
    @JsonProperty(access = JsonProperty.Access.WRITE_ONLY)
    private List<Child> children;
    
    //getters and setters

    @JsonInclude(JsonInclude.Include.NON_NULL)
    @OneToMany(mappedBy = "parent", targetEntity = Child.class, fetch = FetchType.LAZY,cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    public Set<Child> getChildren() {
        return this.children;
    }

    public void setChildren(Set<Child> children) {
        this.children = children;
    }
    
    
}

@Entity
@Table(name = "mychildtable", schema = "myschema", catalog = "mydb")
public class Child implements Serializable {
    private Integer id_child;
    private String description;
   

    @JsonBackReference
    private Parent parent;
    
    //getters and setters
    
}

Following the mentioned article, I changed my code like this:

utx = com.arjuna.ats.jta.UserTransaction.userTransaction();
utx.begin();
em.joinTransaction();

Session session = em.unwrap( Session.class );
for(int i = 0; i< myList.size(); i++){
    if (i > 0 && i % Common.BATCH_SIZE == 0) { //BATCH_SIZE=50
        em.flush(); 
        em.clear();
    }
    Parent myObject = elements.get(i);
    session.update(myObject);
}
utx.commit();

When the list is less than BATCH_SIZE (<50) the edits are made correctly, however, then the flush and clear statements are necessary, I get this error:

detached entity passed to persist: Child

I also tried:

session.flush();
session.clear();

With the exact same error. Is there something I'm missing?

Answer 1

Have you checked if the list contains duplicate objects? If one batch would try to update an object with the same identifier twice, you could run into this issue.