Jakarta Persistence (JPA) Annotation Type

jakarta.persistence.OneToMany

Implemented Interfaces:
Annotation
Target:
Method, Field
Specifies a many-valued association with one-to-many multiplicity.

If the collection is defined using generics to specify the element type, the associated target entity type need not be specified; otherwise the target entity class must be specified. If the relationship is bidirectional, the mappedBy element must be used to specify the relationship field or property of the entity that is the owner of the relationship.

A OneToMany association usually maps a foreign key column or columns in the table of the associated entity. This mapping may be specified using the JoinColumn annotation. Alternatively, a unidirectional OneToMany association is sometimes mapped to a join table using the JoinTable annotation.

The OneToMany annotation may be used within an embeddable class contained within an entity class to specify a relationship to a collection of entities. If the relationship is bidirectional, the mappedBy element must be used to specify the relationship field or property of the entity that is the owner of the relationship.

When the collection is a Map<K,V>, the cascade element and the orphanRemoval element apply to the map value.

Example 1: One-to-Many association using generics 

 // In Customer class:

 @OneToMany(cascade = ALL, mappedBy = "customer")
 public Set getOrders() { return orders; }

 // In Order class:

 @ManyToOne
 @JoinColumn(name = "CUST_ID", nullable = false)
 public Customer getCustomer() { return customer; }

Example 2: One-to-Many association without using generics 

 // In Customer class:

 @OneToMany(targetEntity = com.acme.Order.class, cascade = ALL,
            mappedBy = "customer")
 public Set getOrders() { return orders; }

 // In Order class:

 @ManyToOne
 @JoinColumn(name = "CUST_ID", nullable = false)
 public Customer getCustomer() { return customer; }

Example 3: Unidirectional One-to-Many association using a foreign key mapping 

 // In Customer class:

 @OneToMany(orphanRemoval = true)
 @JoinColumn(name = "CUST_ID") // join column is in table for Order
 public Set getOrders() { return orders; }
Since:
Jakarta Persistence (JPA) 1.0

Annotation Elements

Class<?> targetEntity
(Optional) The entity class that is the target of the association.
Optional only if the collection property is defined using Java generics. Must be specified otherwise.

Defaults to the parameterized type of the collection when defined using generics.

Default:
void/class
Since:
Jakarta Persistence (JPA) 1.0
CascadeType[] cascade
(Optional) The operations that must be cascaded to the target of the association.

Defaults to no operations being cascaded.

When the target collection is a Map<K,V>, the cascade element applies to the map value.

Default:
{}
Since:
Jakarta Persistence (JPA) 1.0
FetchType fetch
(Optional) Whether the association should be lazily loaded or must be eagerly fetched.
The EAGER strategy is a requirement on the persistence provider runtime that the associated entities must be eagerly fetched. The LAZY strategy is a hint to the persistence provider runtime.
Default:
FetchType.LAZY
Since:
Jakarta Persistence (JPA) 1.0
String mappedBy
The field that owns the relationship.
Required unless the relationship is unidirectional.
Default:
""
Since:
Jakarta Persistence (JPA) 1.0
boolean orphanRemoval
(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.
Default:
false
Since:
Jakarta Persistence (JPA) 2.0

Additional JDK methods inherited from java.lang.annotation.Annotation

annotationType(), equals(Object), hashCode(), toString()