Deleting JPA Entity Objects

Existing entity objects can be deleted from the database either explicitly by invoking the removeremove(entity)EntityManager's methodRemove the entity instance.See JavaDoc Reference Page... method or implicitly as a result of a cascade operation.

Explicit Remove

In order to delete an object from the database it has to first be retrieved (no matter which way) and then in an active transaction, it can be deleted using the removeremove(entity)EntityManager's methodRemove the entity instance.See JavaDoc Reference Page... method:

  Employee employee = em.findfind(entityClass, primaryKey)EntityManager's methodFind by primary key.See JavaDoc Reference Page...(Employee.class, 1);

  em.getTransactiongetTransaction()EntityManager's methodReturn the resource-level EntityTransaction object.See JavaDoc Reference Page...().beginbegin()EntityTransaction's methodStart a resource transaction.See JavaDoc Reference Page...();
  em.removeremove(entity)EntityManager's methodRemove the entity instance.See JavaDoc Reference Page...(employee);
  em.getTransactiongetTransaction()EntityManager's methodReturn the resource-level EntityTransaction object.See JavaDoc Reference Page...().commitcommit()EntityTransaction's methodCommit the current resource transaction, writing any 
 unflushed changes to the database.See JavaDoc Reference Page...();

The entity object is physically deleted from the database when the transaction is committed. Embedded objects that are contained in the entity object are also deleted. If the transaction is rolled back and not committed the object is not deleted.

An IllegalArgumentException is thrown by removeremove(entity)EntityManager's methodRemove the entity instance.See JavaDoc Reference Page... if the argument is not an instance of an entity class or if it is a detached entity. A TransactionRequiredExceptionjavax.persistence.TransactionRequiredExceptionJPA exceptionThrown by the persistence provider when a transaction is required but is not active.See JavaDoc Reference Page... is thrown if there is no active transaction when remove is called because operations that modify the database require an active transaction.

Cascading Remove

Marking a reference field with CascadeTypejavax.persistence.CascadeTypeJPA enumDefines the set of cascadable operations that are propagated to the associated entity.See JavaDoc Reference Page....REMOVECascadeType.REMOVEenum constantCascade remove operationSee JavaDoc Reference Page... (or CascadeTypejavax.persistence.CascadeTypeJPA enumDefines the set of cascadable operations that are propagated to the associated entity.See JavaDoc Reference Page....ALLCascadeType.ALLenum constantCascade all operationsSee JavaDoc Reference Page..., which includes REMOVECascadeType.REMOVEenum constantCascade remove operationSee JavaDoc Reference Page...) indicates that removeremove(entity)EntityManager's methodRemove the entity instance.See JavaDoc Reference Page... operations should be cascaded automatically to entity objects that are referenced by that field (multiple entity objects can be referenced by a collection field):

@Entityjavax.persistence.EntityJPA annotationSpecifies that the class is an entity.See JavaDoc Reference Page...
class Employee {
     :
    @OneToOnejavax.persistence.OneToOneJPA annotationDefines a single-valued association to another entity that has
 one-to-one multiplicity.See JavaDoc Reference Page...(cascadeOneToOne.cascadeannotation element(Optional) The operations that must be cascaded to 
 the target of the association.See JavaDoc Reference Page...=CascadeTypejavax.persistence.CascadeTypeJPA enumDefines the set of cascadable operations that are propagated 
 to the associated entity.See JavaDoc Reference Page....REMOVECascadeType.REMOVEenum constantCascade remove operationSee JavaDoc Reference Page...)
    private Address address;
     :
}

In the example above, the Employee entity class contains an address field that references an instance of Address, which is another entity class. Due to the CascadeType.REMOVE setting, when an Employee instance is removed the operation is automatically cascaded to the referenced Address instance, which is then automatically removed as well. Cascading may continue recursively when applicable (e.g. to entity objects that the Address object references, if any).

Orphan Removal

JPA 2 supports an additional and more aggressive remove cascading mode which can be specified using the orphanRemoval element of the @OneToOnejavax.persistence.OneToOneJPA annotationDefines a single-valued association to another entity that has one-to-one multiplicity.See JavaDoc Reference Page... and @OneToManyjavax.persistence.OneToManyJPA annotationDefines a many-valued association with one-to-many multiplicity.See JavaDoc Reference Page... annotations:

@Entityjavax.persistence.EntityJPA annotationSpecifies that the class is an entity.See JavaDoc Reference Page...
class Employee {
     :
    @OneToOnejavax.persistence.OneToOneJPA annotationDefines a single-valued association to another entity that has
 one-to-one multiplicity.See JavaDoc Reference Page...(orphanRemovalOneToOne.orphanRemovalannotation element(Optional) Whether to apply the remove operation to entities that have
 been removed from the relationship and to cascade the remove operation to
 those entities.See JavaDoc Reference Page...=true)
    private Address address;
     :
}

When an Employee entity object is removed the remove operation is cascaded to the referenced Address entity object. In this regard, orphanRemoval=true and cascade=CascadeType.REMOVE are identical, and if orphanRemoval=true is specified, CascadeType.REMOVE is redundant.

The difference between the two settings is in the response to disconnecting a relationship. For example, such as when setting the address field to null or to another Address object.

• If orphanRemoval=true is specified the disconnected Address instance is automatically removed. This is useful for cleaning up dependent objects (e.g. Address) that should not exist without a reference from an owner object (e.g. Employee).
• If only cascade=CascadeType.REMOVE is specified no automatic action is taken since disconnecting a relationship is not a remove operation.

To avoid dangling references as a result of orphan removal this feature should only be enabled for fields that hold private non shared dependent objects.

Orphan removal can also be set for collection and map fields. For example:

@Entityjavax.persistence.EntityJPA annotationSpecifies that the class is an entity.See JavaDoc Reference Page...
class Employee {
     :
    @OneToManyjavax.persistence.OneToManyJPA annotationDefines a many-valued association with one-to-many multiplicity.See JavaDoc Reference Page...(orphanRemovalOneToMany.orphanRemovalannotation element(Optional) Whether to apply the remove operation to entities that have
 been removed from the relationship and to cascade the remove operation to
 those entities.See JavaDoc Reference Page...=true)
    private List<Address> addresses;
     :
}

In this case, removal of an Address object from the collection leads to automatic removal of that object from the database.

DELETE Queries

DELETE queries provide an alternative way for removing entity objects from the database. Deleting objects using a DELETE query may be useful especially when many entity objects have to be deleted in one operation. The DELETE Queries in JPA/JPQL in chapter 4 explains how to use JPA DELETE queries.