Save child objects automatically using JPA Hibernate

I believe you need to set the cascade option in your mapping via xml/annotation. Refer to Hibernate reference example here.

In case you are using annotation, you need to do something like this,

@OneToMany(cascade = CascadeType.PERSIST) // Other options are CascadeType.ALL, CascadeType.UPDATE etc..

I tried the above but I'm getting a database error complaining that the foreign key field in the Child table can not be NULL. Is there a way to tell JPA to automatically set this foreign key into the Child object so it can automatically save children objects?

Well, there are two things here.

First, you need to cascade the save operation (but my understanding is that you are doing this or you wouldn't get a FK constraint violation during inserts in the "child" table)

Second, you probably have a bidirectional association and I think that you're not setting "both sides of the link" correctly. You are supposed to do something like this:

Parent parent = new Parent();
...
Child c1 = new Child();
...
c1.setParent(parent);

List<Child> children = new ArrayList<Child>();
children.add(c1);
parent.setChildren(children);

session.save(parent);

A common pattern is to use link management methods:

@Entity
public class Parent {
    @Id private Long id;

    @OneToMany(mappedBy="parent")
    private List<Child> children = new ArrayList<Child>();

    ...

    protected void setChildren(List<Child> children) {
        this.children = children;
    }

    public void addToChildren(Child child) {
        child.setParent(this);
        this.children.add(child);
    }
}

And the code becomes:

Parent parent = new Parent();
...
Child c1 = new Child();
...

parent.addToChildren(c1);

session.save(parent);

References

• Hibernate Core Reference Guide
  • 1.2.6. Working bi-directional links

Following program describe how bidirectional relation work in hibernate.

When parent will save its list of child object will be auto save.

On Parent side:

    @Entity
    @Table(name="clients")
    public class Clients implements Serializable  {

         @Id
         @GeneratedValue(strategy = GenerationType.IDENTITY)     
         @OneToMany(mappedBy="clients", cascade=CascadeType.ALL)
          List<SmsNumbers> smsNumbers;
    }

And put the following annotation on the child side:

  @Entity
  @Table(name="smsnumbers")
  public class SmsNumbers implements Serializable {

     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     int id;
     String number;
     String status;
     Date reg_date;
     @ManyToOne
     @JoinColumn(name = "client_id")
     private Clients clients;

    // and getter setter.

 }

Main class:

 public static void main(String arr[])
 {
    Session session = HibernateUtil.openSession();
      //getting transaction object from session object
    session.beginTransaction();

    Clients cl=new Clients("Murali", "1010101010");
    SmsNumbers sms1=new SmsNumbers("99999", "Active", cl);
    SmsNumbers sms2=new SmsNumbers("88888", "InActive", cl);
    SmsNumbers sms3=new SmsNumbers("77777", "Active", cl);
    List<SmsNumbers> lstSmsNumbers=new ArrayList<SmsNumbers>();
    lstSmsNumbers.add(sms1);
    lstSmsNumbers.add(sms2);
    lstSmsNumbers.add(sms3);
    cl.setSmsNumbers(lstSmsNumbers);
    session.saveOrUpdate(cl);
    session.getTransaction().commit(); 
    session.close();    

 }