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
determine which options an implementation supports; it returns a
Strings that contain an option string. Chapter 7 presents an example using
this method. Here we enumerate all the optional features and their
The optional features can be grouped into the following categories:
Transaction-related optional features
Each instance managed in a JDO environment must have a unique identifier. The following options are associated with identity:
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 ...