使用 JPA Hibernate 自动保存子对象

in your setChilds, you might want to try looping thru the list and doing something like

child.parent = this;

you also should set up the cascade on the parent to the appropriate values.

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);

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

Here are the ways to assign parent object in child object of Bi-directional relations ?

Suppose you have a relation say One-To-Many,then for each parent object,a set of child object exists. In bi-directional relations,each child object will have reference to its parent.

eg : Each Department will have list of Employees and each Employee is part of some department.This is called Bi directional relations.

To achieve this, one way is to assign parent in child object while persisting parent object

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


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


session.save(parent);

Other way is, you can do using hibernate Intercepter,this way helps you not to write above code for all models.

Hibernate interceptor provide apis to do your own work before perform any DB operation.Likewise onSave of object, we can assign parent object in child objects using reflection.

public class CustomEntityInterceptor extends EmptyInterceptor {


@Override
public boolean onSave(
final Object entity, final Serializable id, final Object[] state, final String[] propertyNames,
final Type[] types) {
if (types != null) {
for (int i = 0; i < types.length; i++) {
if (types[i].isCollectionType()) {
String propertyName = propertyNames[i];
propertyName = propertyName.substring(0, 1).toUpperCase() + propertyName.substring(1);
try {
Method method = entity.getClass().getMethod("get" + propertyName);
List<Object> objectList = (List<Object>) method.invoke(entity);


if (objectList != null) {
for (Object object : objectList) {
String entityName = entity.getClass().getSimpleName();
Method eachMethod = object.getClass().getMethod("set" + entityName, entity.getClass());
eachMethod.invoke(object, entity);
}
}


} catch (NoSuchMethodException | InvocationTargetException | IllegalAccessException e) {
throw new RuntimeException(e);
}
}
}
}
return true;
}


}

And you can register Intercepter to configuration as

new Configuration().setInterceptor( new CustomEntityInterceptor() );

Use org.hibernate.annotations for doing Cascade , if the hibernate and JPA are used together , its somehow complaining on saving the child objects.

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();


}

In short set cascade type to all , will do a job; For an example in your model. Add Code like this . @OneToMany(mappedBy = "receipt", cascade=CascadeType.ALL) private List saleSet;

If you do not have bidirectional relationship and want to only save/update the the single column in the child table, then you can create JPA repository with child Entity and call save/saveAll or update method.

Note: if you come across FK violations then it means your postman request having primary and foreign key ids is not matching with generated ids in child table , check the ids in your request and child table which your are going to update(they should match/if they don't means you get FK violations) whatever ids generated while saving the parent and child in before transactions, those ids should match in your second call when you try to update the single column in your child table.

Parent:

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


@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private UUID customerId ;
     

@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name ="child_columnName", referencedColumnName=
"parent_columnName")
List<Accounts> accountList;
}

Child :

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


@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private UUID accountid;
         

        

}

In JPA @*To* relationships both parent and child entities must be cross assigned before (parent) saving.