Annotation Elements

CascadeType[] cascade

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

By default no operations are cascaded.

Default value: {}

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.

Default value: javax.persistence.FetchType.EAGER

String mappedBy

Optional) The field that owns the relationship. This element is only specified on the inverse (non-owning) side of the association.

Default value: ""

boolean optional

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

Default value:  true

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 value:  false

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 value:  void.class

@OneToOne

Defines a single-valued association to another entity that has one-to-one multiplicity.

• cascade
• fetch
• mappedBy
• optional
• orphanRemoval
• targetEntity

One-to-one association that maps a foreign key column

Customer

ID

...

CUSTREC_ID

CustomerRecord

ID

...

One-to-one association that maps a foreign key column

// On Customer class:
 
    @OneToOne(optional=false)
    @JoinColumn(
      name="CUSTREC_ID", unique=true, nullable=false, updatable=false)
    public CustomerRecord getCustomerRecord() { return customerRecord; }
 
    // On CustomerRecord class:
 
    @OneToOne(optional=false, mappedBy="customerRecord")
    public Customer getCustomer() { return customer; }

One-to-one association that assumes both the source and target share the same primary key values.

Employee

ID

...

EmployeeInfo

ID

...

One-to-one association that assumes both the source and target share the same primary key values.

// On Employee class:
 
@Entity
public class Employee {
  @Id Integer id;
 
  @OneToOne @MapsId
  EmployeeInfo info;
  ...
}
 
// On EmployeeInfo class:
 
@Entity
public class EmployeeInfo {
  @Id Integer id;
  ...
}

Embeddable Classes in Entities ?

Address

id

street1

city

province

zip

plusFour

country

...

Embeddable Classes in Entities ?

@Embeddable
public class ZipCode {
  String zip;
  String plusFour;
...
}
This embeddable class is used by the Address entity:

@Entity
public class Address {
  @Id
  protected long id
  String street1;
  String street2;
  String city;
  String province;
  @Embedded
  ZipCode zipCode;
  String country;
...
}

One-to-one association from an embeddable class to another entity.

Employee

id

officeNumber

parkingSpotId

...

ParkingSpot

id

garage

...

One-to-one association from an embeddable class to another entity.

@Entity
public class Employee {
   @Id int id;
   @Embedded LocationDetails location;
   ...
}
 
@Embeddable
public class LocationDetails {
   int officeNumber;
   @OneToOne ParkingSpot parkingSpot;
   ...
}
 
@Entity
public class ParkingSpot {
   @Id int id;
   String garage;
   @OneToOne(mappedBy="location.parkingSpot") Employee assignedTo;
    ... 
}

@OneToMany

Defines a many-valued association with one-to-many multiplicity.

• cascade
• fetch
• mappedBy
• orphanRemoval
• targetEntity

One-to-Many association using generics

Customer

id

...

Order

id

CUST_ID

...

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; }

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; }

@ManyToOne

Defines a single-valued association to another entity class that has many-to-one multiplicity.

• cascade
• fetch
• optional
• targetEntity

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

Employee

id

jobDescription

pmId

...

ProgramManger

id

...

 @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;
 }

@ManyToMany

Defines a many-valued association with many-to-many multiplicity.

• cascade
• fetch
• mappedBy
• targetEntity

Customer

id

...

Phone

id

...

CUST_PHONES

cid

pid

// In Customer class:
 
@ManyToMany
@JoinTable(name="CUST_PHONES")
public Set<PhoneNumber> getPhones() { return phones; }
 
// In PhoneNumber class:
 
@ManyToMany(mappedBy="phones")
public Set<Customer> getCustomers() { return customers; }

 // In Customer class:
 
@ManyToMany(targetEntity=com.acme.PhoneNumber.class)
public Set getPhones() { return phones; }
 
// In PhoneNumber class:
 
@ManyToMany(targetEntity=com.acme.Customer.class, mappedBy="phones")
public Set getCustomers() { return customers; }

// In Customer class:
 
@ManyToMany
@JoinTable(name="CUST_PHONE",
    joinColumns=
        @JoinColumn(name="CUST_ID", referencedColumnName="ID"),
    inverseJoinColumns=
        @JoinColumn(name="PHONE_ID", referencedColumnName="ID")
    )
public Set<PhoneNumber> getPhones() { return phones; }
 
// In PhoneNumberClass:
 
@ManyToMany(mappedBy="phones")
public Set<Customer> getCustomers() { return customers; }