Java Data Objects (JDO)

Modeling using JDO

Gopalan Suresh Raj

Persistence management is delegated to JDO. The user never needs to implement the actual persistence infrastructure if he chooses to go with a JDO solution. Therefore, the user is free to design his domain object model without unduly constraining his design and be assured that the persistence mechanism is automatically implemented for him.

JDO does not affect the visibility modifiers of the user's domain classes, or mandate the presence of accessor and mutator methods.

JDO does not affect the way in which persistence-capable domain classes manipulate application exceptions.

The application of default persistence modifiers by JDO enhancers allows JDO persistence descriptors to be relatively straightforward documents.

In general it is classes in the domain object model that need to be made persistence-capable. Application, GUI and other infrastructure classes are generally not persistence-capable.

Each persistence manager has at most one active transaction associated with it. The same Transaction instance can be used to begin and commit successive transactions for the life of the persistence manager.

Instances of persistence-capable classes instantiated directly with the new operator are Transient.

When making Transient objects Persistent, it is more common to employ “Persistence by Reachability” than to explicitly invoke makePersistent().

Detachment from the object graph and Deletion from the data store are two separate concepts in JDO.

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