Cascade Operations and Relationships (The Java EE 6 Tutorial)

The Java EE 6 Tutorial

Cascade Operations and Relationships

Entities that use relationships often have dependencies on the existence of the other entity in the relationship. For example, a line item is part of an order; if the order is deleted, the line item also should be deleted. This is called a cascade delete relationship.

The javax.persistence.CascadeType enumerated type defines the cascade operations that are applied in the cascade element of the relationship annotations. Table 20–1 lists the cascade operations for entities.

Table 20–1 Cascade Operations for Entities


Cascade Operation	Description
`ALL`	All cascade operations will be applied to the parent entity’s related entity. `All` is equivalent to specifying `cascade={DETACH, MERGE, PERSIST, REFRESH, REMOVE}`
`DETACH`	If the parent entity is detached from the persistence context, the related entity will also be detached.
`MERGE`	If the parent entity is merged into the persistence context, the related entity will also be merged.
`PERSIST`	If the parent entity is persisted into the persistence context, the related entity will also be persisted.
`REFRESH`	If the parent entity is refreshed in the current persistence context, the related entity will also be refreshed.
`REMOVE`	If the parent entity is removed from the current persistence context, the related entity will also be removed.

Cascade delete relationships are specified using the cascade=REMOVE element specification for @OneToOne and @OneToMany relationships. For example:

@OneToMany(cascade=REMOVE, mappedBy="customer")
public Set<Order> getOrders() { return orders; }