Primary Key Generation Using Oracle's Sequence
Oracle provides the 'sequence' utility to automatically generate unique primary keys. To use this utility to auto-generate primary keys for a CMP entity bean, you must create a sequence table and use the ejbgen:automatic-key-generation tag to point to this table.
Learn how to define an auto increment primary key in PostgreSQL. Get instructions on learning how to use the serial data type nd how to use a custom sequence.
In your Oracle database, you must create a sequence table that will create the primary keys, like is shown in the following example:
This creates a sequences of primary key, starting with 1, followed by 2, 3, and so forth. The sequence table in the example uses the default increment 1, but you can change this by specifying the increment keyword, such as increment by 3. When you do the latter, you must specify the exact same value in the cache-size attribute of the ejbgen:automatic-key-generation tag:
If you have specified automatic table creation in the CMP bean's project settings, the sequence table will be created automatically when the entity bean is deployed. For more information, see @ejbgen:jar-settings Annotation. For more information on the definition of a CMP entity bean, see below.
Primary Key Generation Using SQL Server's IDENTITY
In SQL Server (2000) you can use the 'IDENTITY' keyword to indicate that a primary-key needs to be auto-generated. The following example shows a common scenario where the first primary key value is 1, and the increment is 1:
In the CMP entity bean definition you need to specify SQLServer(2000) as the type of automatic key generator you are using. You can also provide a cache size:
If you have specified automatic table creation in the CMP bean's project settings, the sequence table will be created automatically when the entity bean is deployed. For more information, see @ejbgen:jar-settings Annotation. For more information on the definition of a CMP entity bean, see below.
Note. The SQLServer2000 option is the same as SQLServer, except that SQLServer uses @@IDENTITY column to get the generated key value and SQLServer2000 uses the SCOPE_IDENTITY() function instead.
Primary Key Generation Using a Named Sequence Table
A named sequence table is similar to the Oracle sequence functionality in that a dedicated table is used to generate primary keys. However, the named sequence table approach is vendor-neutral. To auto-generate primary keys this way, create a named sequence table using the two SQL statements shown in the example:
In the CMP entity bean definition you need to specify the named sequence table as the type of automatic key generator you are using. You can also provide a cache size:
If you have specified automatic table creation in the CMP bean's project settings, the sequence table will be created automatically when the entity bean is deployed. For more information, see @ejbgen:jar-settings Annotation. For more information on the definition of a CMP entity bean, see the next section.
Note. When you specify a cache-size for a named sequence table, a series of unique values are reserved for entity bean creation. When a new cache is necessary, a second series of unique values is reserved, under the assumption that the first series of unique values was entirely used. This guarantees that primary key values are always unique, although it leaves open the possibility that primary key values are not necessarily sequential. For instance, when the first series of values is 10...20, the second series of values is 21-30, even if not all values in the first series were actually used to create entity beans.
Defining the CMP Entity Bean
When defining a CMP entity bean that uses one of the primary key generators, you point to the name of the primary key generator table to obtain primary keys, using the ejbgen:automatic-key-generation tag. Also, you must define a primary key field of type Integer or Long, to set and get the auto-generated primary key. However, the ejbCreate method does not take a primary key value as an argument. Instead the EJB container adds the correct primary key to the entity bean record.
The following example shows what the entity bean might look like. Notice that the bean uses the named sequence option describe above, and that ejbCreate method does not take a primary key: Related Topics
Primary Key Generation Using Oracle's Sequence
Oracle provides the
sequence
utility to automatically generate unique primary keys. To use this utility to auto-generate primary keys for a CMP entity bean, you must create a sequence table and use the @AutomaticKeyGeneration annotation to point to this table.In your Oracle database, you must create a sequence table that will create the primary keys, as shown in the following example:
This creates a sequences of primary key values, starting with 1, followed by 2, 3, and so forth. The sequence table in the example uses the default increment 1, but you can change this by specifying the increment keyword, such as increment by 3. When you do the latter, you must specify the exact same value in the cacheSize attribute of the @AutomaticKeyGeneration annotation:
If you have specified automatic table creation in the CMP bean's project settings, the sequence table will be created automatically when the entity bean is deployed. For more information, see @JarSettings Annotation. For more information on the definition of a CMP entity bean, see below.
Auto Increment Primary Key Oracle 11g
Primary Key Generation Using SQL Server's IDENTITY
In SQL Server you can use the
IDENTITY
keyword to indicate that a primary-key needs to be auto-generated. The following example shows a common scenario where the first primary key value is 1, and the increment is 1:In the CMP entity bean definition you need to specify SQLServer(2000) as the type of automatic key generator you are using. You can also provide a cache size:
If you have specified automatic table creation in the CMP bean's project settings, the sequence table will be created automatically when the entity bean is deployed. For more information, see @JarSettings Annotation. For more information on the definition of a CMP entity bean, see below.
Primary Key Generation Using a Named Sequence Table
A named sequence table is similar to the Oracle sequence functionality in that a dedicated table is used to generate primary keys. However, the named sequence table approach is vendor-neutral. To auto-generate primary keys this way, create a named sequence table using the two SQL statements shown in the example:
In the CMP entity bean definition you need to specify the named sequence table as the type of automatic key generator you are using. You can also provide a cache size:
If you have specified automatic table creation in the CMP bean's project settings, the sequence table will be created automatically when the entity bean is deployed. For more information, see @JarSettings Annotation. For more information on the definition of a CMP entity bean, see the next section.
Note. When you specify a cacheSize value for a named sequence table, a series of unique values are reserved for entity bean creation. When a new cache is necessary, a second series of unique values is reserved, under the assumption that the first series of unique values was entirely used. This guarantees that primary key values are always unique, although it leaves open the possibility that primary key values are not necessarily sequential. For instance, when the first series of values is 10...20, the second series of values is 21-30, even if not all values in the first series were actually used to create entity beans.
Defining the CMP Entity Bean
When defining a CMP entity bean that uses one of the primary key generators, you use the the @AutomaticKeyGeneration annotation to point to the name of the primary key generator table to obtain primary keys. Also, you must define a primary key field of type Integer or Long to set and get the auto-generated primary key. However, the ejbCreate method does not take a primary key value as an argument. Instead the EJB container adds the correct primary key to the entity bean record.
Oracle Drop Primary Key
The following example shows what the entity bean might look like. Notice that the bean uses the named sequence option described above, and that ejbCreate method does not take a primary key:Auto Generate Primary Key Oracle Chart
Related Topics