PersistenceManager

PersistenceManager is a software component that mediates between an application and a persistent data store, coordinating the lifecycle of in-memory objects and their durable representations. It provides the core APIs for creating, reading, updating, and deleting persistent objects, as well as for issuing queries, managing identities, and handling transactional boundaries. The goal is to abstract the details of the underlying datastore and to present a uniform interface for persistence operations.

In the Java Data Objects (JDO) standard, PersistenceManager is an interface that defines the primary persistence operations. Common methods include making objects persistent (makePersistent, makePersistentAll), deleting objects (deletePersistent, deletePersistentAll), retrieving objects by identity (getObjectById), and creating queries (newQuery) or obtaining roots of all instances of a class (getExtent). Transactions are controlled through the currentTransaction API, and a PersistenceManager is typically obtained from a PersistenceManagerFactory, with proper closure after use.

Applications often configure a PersistenceManagerFactory to connect to a specific datastore, such as Google App Engine’s Datastore, and then obtain a PersistenceManager instance for a scope like a request. This manager handles persistence contexts, caching behavior, and the translation between objects and their stored representations, simplifying data access patterns.

See also: Java Data Objects, EntityManager, Datastore, Transactions. A PersistenceManager shares a similar role with the JPA EntityManager but belongs to the JDO ecosystem; both provide a persistence context and query capabilities, though they are part of different persistence specifications.