Java Reference
In-Depth Information
Bidirectional one-to-one
In unidirectional relationships, navigating the domain model can be done only one way. In
but you can't go the other way—you can't reach the
User
object through
BillingInfo
.
In bidirectional relationships, JPA puts domain model references together to enable you to
go both ways. Bidirectional one-to-one relationships are implemented using
@OneToOne
annotations pointing to each other on both sides of the relationship. Let's see how this
works in the next listing by updating the code from
listing 9.17
.
Listing 9.18. Bidirectional one-to-one relationship
In this listing, the
User
class has a relationship to the
BillingInfo
class through the
billingInfo
property . This is no different than the unidirectional one-to-one rela-
tionship of
listing 9.17
. But in this example the relationship is bidirectional because the
BillingInfo
class also has a reference to the
User
class through the
user
property
. The
@OneToOne
annotation on the
user
property uses
mappedBy
and
optional
.
The
mappedBy="billingInfo"
configuration tells JPA that the “owning” side of the
relationship is the
User
class's
billingInfo
property. The
optional= "false"
configuration tells JPA that
BillingInfo
can't exist without a
User
. This is interesting
because the
@OneToOne
annotation in
User
doesn't have this configuration. This means
