To generate unique datastore identity primary key values, Kodo JDO typically uses a kodo.jdbc.schema.SequenceFactory internally. The default sequence factory implementation in use is controlled by the kodo.jdbc.SequenceFactory configuration property. You can also declare that a given class uses a specific sequence factory through the jdbc-sequence-factory metadata extension.

Using a sequence factory allows coarse-grained control over primary key values while maintaining the simplicity of using datastore identity. Furthermore, it is possible to use the sequence factory yourself to make default assignments to the fields of application identity instances. This gives you the fine-grained control of application identity, without the burden of coming up with your own system to generate unique primary key values. Kodo can also automatically assign values from this sequence factory. See Section 5.2.4.3, “Sequence-Assigned”.

Kodo JDO ships with four available sequence factories, and you are free to substitute your own as well.

kodo.jdbc.SequenceFactory: native(TableName=SEQTABLE, \
    Format="SELECT {0}.NEXT FROM {1}")

The assigned sequence factory for the class/configuration can be used to assign field values on flush. This is especially useful for generating primary key values in application identity classes. See Section 5.2.4.3, “Sequence-Assigned”.

As mentioned above, you may want to use the sequence factory in your application. The example below demonstrates how to do so.

import kodo.runtime.*;

...

SequenceGenerator gen = KodoHelper.getSequenceGenerator (pm, MyPCClass.class);
pm.currentTransaction ().begin ();

MyPCClass pc1 = new MyPCClass ();
pc1.setPrimaryKey (gen.getNext ().longValue ());
pm.makePersistent (pc1);

MyPCClass pc2 = new MyPCClass ();
pc2.setPrimaryKey (gen.getNext ().longValue ());
pm.makePersistent (pc2);

pm.currentTransaction ().commit ();

Some databases allow you to define columns that are automatically assigned a unique numeric value when a record is inserted. In many databases, this value is monotonically increasing. Thus, Kodo JDO refers to these columns as auto-increment columns.

Any field can use an auto-increment column in Kodo, but they are most often used for primary key fields under application identity, or for the primary key column under datastore identity. Before you decide to use auto-increment columns, you should be aware of the following restrictions:

The jdbc-auto-increment metadata extension controls Kodo's use of auto-increment columns. Placing this extension beneath the <class> element indicates that the datastore identity primary key column of the class will auto-increment. Placing it on a <field> element means that the field's column will auto-increment. You must specify these extensions even if you do not use Kodo to create your schema, because Kodo cannot reliably determine which columns are auto-incrementing through the JDBC driver alone.

<jdo>
  <package name="com.xyz">
    <class name="Person">
      <extension vendor-name="kodo" key="jdbc-auto-increment" value="true"/>
    </class>
    <class name="Form" objectid-class="FormId">
      <field name="id" primary-key="true">
        <extension vendor-name="kodo" key="jdbc-auto-increment" value="true"/>
      </field>
    </class>
  </package>
</jdo>

Sequence factories can be applied to classes using application identity as well. This is useful for generating unique primary key values automatically. These values will be generated when the owning instance is made persistent. Combined with single field identity, this feature simplifies the use of application identity. This field level extension can be used for any long compatible field (i.e. long, short, integer or their wrapper types).

Kodo will use the same sequence factory assigned to the class to generate the next value. If multiple fields are marked as sequence assigned, Kodo will assign unique values for each field. If a non-default value was already assigned when PersistenceManager.makePersistent () (or implied during persistence by reachability), the field will not be assigned a value.

<jdo>
  <package name="com.xyz">
    <class name="Company" objectid-class="CompanyId">
      <field name="id" primary-key="true">
        <extension vendor-name="kodo" key="sequence-assigned" value="true"?>
      </field>
    </class>
  </package>
</jdo>