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CRUD Database Operations with JPA

Given an EntityManager, em, that represents a JPA connection to the object database, we can use it to store, retrieve, update and delete database objects. Storing New Entity Objects The following code fragment stores 1,000 Point objects in the database: em.getTransaction().begin(); for (int i

Locking in JPA

in ObjectDB (and in JPA) is always at the database object level, i.e. each database object is locked separately. Optimistic locking is applied on transaction commit. Any database object ... is being performed on an old version of a database object, for which another update has already been committed

JPA Primary Key

Every entity object that is stored in the database has a primary key. Once assigned, the primary key cannot be modified. It represents the entity object as long as it exists in the database. As an object database, ObjectDB supports implicit object IDs, so an explicitly defined primary key is not

FROM clause (JPQL / Criteria API)

The FROM clause declares query identification variables that represent iteration over objects in ... a program, since both are used for iteration over objects. Range Variables Range variables are query identification variables that iterate over all the database objects of a specific entity class

GROUP BY and HAVING clauses

properties of generated groups instead of individual objects and fields. The position of a GROUP BY ... clause. When a GROUP BY clause exists in a JPQL query, database objects (or tuples of database objects ... over all the Country objects in the database. The GROUP BY clause groups these Country objects by

Shared (L2) Entity Cache

Every EntityManager owns a persistence context, which is a collection of all the entity objects ... an entity object that is already managed by the EntityManager returns the existing instance from the persistence context, rather than a new instantiated entity object. The scope of the persistence context

Running JPA Queries

when exactly one result object is expected. Query.getResultList - for general use in any other case ... - for use when exactly one result object is expected. TypedQuery.getResultList - for general use in any ... (with getResultList) The following query retrieves all the Country objects in the database. Because multiple

Embedded Object inside another embedded object - is that possible?

I have an entity with an embedded object - it works fine. Now I am trying to add an embedded object inside the first level embedded object - but it does not seem to store it and does not throw either... I was wondering if it was a limitation or not? has anyone tried this before? Thanks


. This exception contains a nested JDOOptimisticVerificationException for each object that failed ... 1.0 void deletePersistent(Object pc) Delete the persistent instance from the data store. Delete ... . The data store object will be removed at commit. Unlike makePersistent, which makes the closure


As explained in chapter 2, entity objects can be deleted from the database by: Retrieving the entity objects into an EntityManager. Removing these objects from the EntityManager within an active ... an alternative way for deleting entity objects. Unlike SELECT queries, which are used to retrieve data from