Java Reference
In-Depth Information
Sequence
The sequence strategy uses a database sequence to get auto-incrementing unique numbers.
This strategy is most popular with Oracle because Oracle doesn't have the identity column
type discussed in the previous section. To configure JPA to use a database sequence as the
primary-key generator, first create the sequence. The following SQL shows how to create
a sequence in Oracle:
CREATE SEQUENCE USER_SEQUENCE START WITH 1 INCREMENT BY 10;
Next, use
@SequenceGenerator
to configure a connection to the sequence; then con-
figure
@GeneratedValue
to use this sequence generator. The following listing shows
what the
User
object would look like using the sequence strategy.
Listing 9.13. Sequence strategy
In this listing there's first a
@SequenceGenerator
with
name
set to
USER_SEQUENCE _GENERATOR
. This is the internal JPA name for this sequence,
and other JPA annotations will use this name when referring to the sequence. The
se-
quenceName
attribute is set to the actual name of the sequence in the database, which
in this case is
USER_SEQUENCE
. For the
@GeneratedValue
annotation, the
strategy
is set to
Generation_Type.SEQUENCE
and the
generator
is set to
the internal JPA name of the sequence
.
A @SequenceGenerator
is sharable across the entire persistence unit. This means
a
@SequenceGenerator
doesn't need to be defined in the class it's used. Any
