Java Data Objects

Optional Features

JDO defines some features that are optional; JDO-compliant implementations are not required to implement them. Each optional feature is identified by a unique name, which includes a javax.jdo.option prefix. You can call the supportedOptions( ) method, defined in PersistenceManagerFactory, to determine which options an implementation supports; it returns a Collection of Strings that contain an option string. Chapter 7 presents an example using this method. Here we enumerate all the optional features and their names.

The optional features can be grouped into the following categories:

• Identity options

• Optional collections

• Transaction-related optional features

Identity Options

Each instance managed in a JDO environment must have a unique identifier. The following options are associated with identity:

• javax.jdo.option.ApplicationIdentity

• javax.jdo.option.DatastoreIdentity

• javax.jdo.option.NonDurableIdentity

• javax.jdo.option.ChangeApplicationIdentity

The first three options represent different kinds of identity. The fourth option indicates whether you can change the value of the fields that represent the application identity of an instance.

Support for each form of identity is optional. However, an implementation must support either datastore or application identity, and may support both. In Chapter 1 we used datastore identity, which is supported by all of the current JDO implementations. Until we cover identity in depth in Chapter 10, all of our examples will use datastore ...