Java Data Objects

Reading Outside a Transaction

NontransactionalRead allows your application to access the datastore without ever beginning a transaction; it also allows you to access the datastore and read cached instances and fields between completing one transaction and beginning the next. This allows read-only applications nearly full access to the features of JDO, without the overhead of beginning and completing transactions. Access in the NontransactionalRead case includes iterating extents, querying the datastore, accessing persistent field values, and navigating among instances using persistent relationships.

Note that you must always have an active transaction in order to insert new persistent instances, delete existing instances, or change existing data in the datastore.

One use for the NontransactionalRead mode of operation is to access slowly changing information. For example, access to the MediaContent instances can be nontransactional, because in most cases the information is static. At times, the datastore might be updated with new MediaContent instances, but for the most part, the information does not change.

When executing your application outside a transaction, the cache contains persistent instances whose field values came from the datastore, but there is no guarantee that the field values are consistent with the current datastore contents, or are even consistent with other field values from the same persistent instance. This is because field values are retrieved from the datastore ...