Automatic Primary Key Generation

Chapter 8 Creating J2EE Applications for BEA WebLogic

Automatic Primary Key Generation

WebLogic Server supports an automatic primary key generation feature for container-managed-persistence (CMP). Generated key support is provided in two ways:

Using DBMS primary key generation. This option uses a set of deployment descriptors that are specified at compile time to generate container code which is used in conjunction with a supported database to provide key generation support.

With this option, the container defers all key generation to the underlying database. To enable this feature, you specify the name of the supported DBMS and the generator name, if required by the database. The CMP code handles all of the details of implementing this feature.
Using Bean Provider Designated Named Sequence table. This option uses a user named and created database table which has a schema specified by WebLogic. The container uses this table to generate the keys.

With this option, you name a table that holds the current primary key value. The table consists of a single-row with a single column as defined by the following statement:

CREATE table_name (SEQUENCE int)
INSERT into table_name VALUES (0)

In the weblogic-cmp-rdbms-jar.xml file, set the key_cache_size element to specify how many primary key values a database SELECT and UPDATE will fetch at one time. The default value of key_cache_size is 1. We recommend that you set this element to a value of >1, to minimize database accesses and to improve performance.

At this time, WebLogic Server only provides DBMS primary key generation support for Oracle and Microsoft SQL Server. However, named/sequence tables can be used with other unsupported databases. This feature is intended for use with simple (non-compound) primary keys.

Note: This feature is supported for the CMP 2.0 container only, there is no automatic primary key generation support for CMP 1.1. For 1.1 beans, you must use Bean-Managed-Persistence (BMP.)

Note: The key field must be declared to be of type java.lang.Integer in the abstract `get' and `set' methods of the bean.