Module jakarta.persistence

Package jakarta.persistence

Annotation Interface ManyToOne

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

Specifies a single-valued association to another entity class that has many-to-one multiplicity. It is not usually necessary to specify the target entity explicitly since it can usually be inferred from the type of the object being referenced.

If the relationship is bidirectional, the non-owning OneToMany entity side must use the mappedBy element to specify the relationship field or property of the entity that is the owner of the relationship.

A ManyToOne association usually maps a foreign key column or columns. This mapping may be specified using the JoinColumn annotation. Alternatively, an optional OneToOne association is sometimes mapped to a join table using the JoinTable annotation.

The ManyToOne annotation may be used within an embeddable class to specify a relationship from the embeddable class to an entity class. If the relationship is bidirectional, the non-owning OneToMany entity side must use the mappedBy element of the OneToMany annotation to specify the relationship field or property of the embeddable field or property on the owning side of the relationship. The dot (.) notation syntax must be used in the mappedBy element to indicate the relationship attribute within the embedded attribute. The value of each identifier used with the dot notation is the name of the respective embedded field or property.

Example 1:

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

Example 2:

@Entity
public class Employee {
    @Id
    int id;
    @Embedded
    JobInfo jobInfo;
    ...
}

@Embeddable
public class JobInfo {
    String jobDescription;
    @ManyToOne
    ProgramManager pm; // Bidirectional
}

@Entity
public class ProgramManager {
    @Id
    int id;
    @OneToMany(mappedBy = "jobInfo.pm")
    Collection<Employee> manages;
}

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.
boolean	optional	(Optional) Whether the association is optional.
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.

Defaults to the type of the field or property that stores the association.

Default:

void.class

cascade

CascadeType[] cascade

(Optional) The operations that must be cascaded to the target of the association.

By default no operations are cascaded.

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 entity must be eagerly fetched.
• The LAZY strategy is a hint to the persistence provider runtime.

If not specified, defaults to EAGER.

Default:

EAGER

optional

boolean optional

(Optional) Whether the association is optional. If set to false then a non-null relationship must always exist.

May be used in schema generation to infer that the mapped foreign key column is not null.

Default:

true