Module jakarta.persistence

Package jakarta.persistence

Annotation Interface OneToMany

@Target({METHOD,FIELD})
@Retention(RUNTIME)
public @interface OneToMany

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, 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<Order> 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<Order> getOrders() { return orders; }

Since:

1.0

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element	Description
CascadeType[]	cascade	(Optional) The operations that must be cascaded to the target of the association.
FetchType	fetch	(Optional) Whether the association should be lazily loaded or must be eagerly fetched.
String	mappedBy	The field that owns the relationship.
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.
Class<?>	targetEntity	(Optional) The entity class that is the target of the association.

Element Details

targetEntity

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

cascade

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, the cascade element applies to the map value.

Default:

{}

fetch

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:

LAZY

mappedBy

String mappedBy

The field that owns the relationship. Required unless the relationship is unidirectional.

Default:

""

orphanRemoval

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.

Since:

2.0

Default:

false