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() );
