Prior knowledge or experience in database programming (SQL, JDBC, ORM, JPA, etc.) is not required, but some background in using the Java language is essential.
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The Java Persistence API (JPA) provides various ways to retrieve objects from the database. The retrieval of objects does not require an active transaction because it does not change the content of the database. The persistence context serves as a cache of retrieved entity objects. If a requested
Method javax.jdo.PersistenceManager void retrieve( Object pc, boolean useFetchPlan ) Retrieve field ... intends to use the instance, and its field values must be retrieved. If the useFetchPlan parameter ... the current fetch plan to determine which fields to load and which instances to retrieve. Since: JDO 2.0
Method javax.jdo.PersistenceManager void retrieve( Object pc ) Retrieve field values of an instance ... , and its field values must be retrieved. The PersistenceManager might use policy information about the class to retrieve associated instances. Parameters: pc - the instance Since: JDO 1.0
or queried directly (an embedded object can only be retrieved using a reference from its containing ... in object retrieval, as shown in the next section (section 6.3). ObjectDB supports two identifying ... can easily start from them, as explained in the next section. 6.3 Retrieving Persistent Objects
There are various ways to retrieve objects from an ObjectDB database, as shown in section 6.3. An Extent, for instance, can be used to retrieve all the instances of a specified persistent class. When a more selective retrieval is needed, JDOQL (JDO Query Language) is used. JDOQL for JDO is like SQL
Explains how to use JPA for CRUD database operations (persist, retrieve, update, remove).
Explains how to store, retrieve, update and delete entity objects using JPA.
it to store, retrieve, update and delete database objects. Storing New Entity Objects The following ... a Double object reflecting the average x value of all the Point objects in the database. Retrieving Existing Entities The Retrieving Entities section in chapter 3 describes several methods for retrieving
that it manages. The persistence context serves as a first level cache. An attempt to retrieve ... automatically: On retrieval - shared cache is used for entity objects that are not in the persistence context. If an entity object is not available also in the shared cache - it is retrieved from
(); em.clear(); em.close(); // Try to retrieve parent and children using ... is now closed, let's check if children are retrieved em.close(); emf.close ... (); em.close(); // Try to retrieve parent and children using left join fetch em = emf