Java Reference
In-Depth Information
because with the single-table strategy, there's only a single table, so bidder and seller data
will be stored in the
USERS
table together. To tell the data apart, the
Bidder
class uses
@DiscriminatorValue
to configure JPA to store the value
"B"
in the
USERS
table
discriminator column
USER_TYPE
.
Seller
does the same thing for the value
"S"
. Using
@DiscriminatorValue
is optional, and the default value will be the name
of the class—that is,
Seller
for the
Seller
object.
9.5.2. Joined-tables strategy
In the joined-tables strategy, you use a one-to-one relationship between the domain model
and the tables in the database. In effect, the joined-tables strategy involves creating separate
tables for each entity in the domain model. Take a look at
figure 9.11
to see how the joined-
tables strategy works.
Figure 9.11. Store all user data using a one-to-one mapping from Java objects to tables.
users (
USERNAME
). The
BIDDERS
and
SELLERS
tables are children of
USERS
. You can
see that they're children because the
USER_ID
column in
BIDDERS
and
SELLERS
is a
foreign key that points back to the
USER_ID
column in
USERS
. The
BIDDERS
table holds
only bidder-specific data (
BID_FREQUENCY
), whereas the
SELLERS
table holds seller-
specific data (
CREDIT_WORTH
). These tables have a one-to-one mapping back to the Java
domain model. So the
User
entity maps to the
USERS
table,
Seller
to
SELLERS
, and
