The orphanRemoval property allows you to easily manage OneToMany and OneToOne relationships. If a relationship has orphanRemoval set to true, then whenever a child is removed from the parent entity it will also be deleted from the database.

But when used in combination with Play’s POJO binding, it can cause some unexpected errors. Consider the following example:

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@Entity
public class Parent extends Model {
  @OneToMany(cascade=CascadeType.ALL, orphanRemoval=true)
  List<Child> childs;
}

And our Controller:

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public ParentController extends Controller {
  public static void update(Parent parent) {
    parent.merge();
    parent.save();
    render(parent);
  }
}

This will throw the following exception: PersistenceException occured : org.hibernate.HibernateException: A collection with cascade="all-delete-orphan" was no longer referenced by the owning entity instance: models.Parent.childs

The problem

To make the orphanRemoval work Hibernate has to keep track of the Collection that is referencing the childs. When update() is called, the childs List is assigned a new instance, this is what causes the PersistenceException.

The solution

We can easily solve this by providing a setter for childs which will prevent it from being assigned a new instance. Here is the fixed Parent model:

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@Entity
public class Parent extends Model {
  @OneToMany(cascade=CascadeType.ALL, orphanRemoval=true)
  List<Child> childs;

  public void setChilds(List<Child> newChilds) {
    this.childs.clear();
    if (newChilds != null) {
      this.childs.addAll(newChilds);
    }
  }
}