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JPA Entity Fields

Fields of persistable user defined classes (entity classes, embeddable classes and mapped ... and inverse fields) can be used in both entity classes and embeddable classes. However, the last two groups (primary key and version fields) can only be used in entity classes. Primary key fields

Retrieving JPA Entity Objects

of the database. The persistence context serves as a cache of retrieved entity objects. If a requested entity object is not found in the persistence context a new object is constructed and filled with data that is retrieved from the database (or from the L2 cache - if enabled). The new entity object

Working with JPA Entity Objects

Entity objects are in-memory instances of entity classes (persistable user defined classes ... requires using entity objects for many operations, including storing, retrieving, updating and deleting database objects. Entity Object Life Cycle The life cycle of entity objects consists of four states

Storing JPA Entity Objects

New entity objects can be stored in the database either explicitly by invoking the persist method ... an instance of the Employee entity class in the database: Employee employee = new Employee("Samuel ... and changes its state to Managed. The new entity object is stored in the database when the transaction

Detached Entity Objects

Detached entity objects are objects in a special state in which they are not managed by any EntityManager but still represent objects in the database. Compared to managed entity objects, detached ... that have been loaded before detachment should be used. Changes to detached entity objects are not stored in

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 newly instantiated entity object. The scope of the persistence context

Defining a JPA Entity Class

To be able to store Point objects in the database using JPA we need to define an entity class. A JPA entity class is a POJO (Plain Old Java Object) class, i.e. an ordinary Java class that is marked ... to serializable classes, which are marked as having the ability to be serialized. The Point Entity

Deleting JPA Entity Objects

Existing entity objects can be deleted from the database either explicitly by invoking the remove ... (); The entity object is physically deleted from the database when the transaction is committed. Embedded objects that are contained in the entity object are also deleted. If the transaction is rolled

Updating JPA Entity Objects

Modifying existing entity objects that are stored in the database is based on transparent ... Once an entity object is retrieved from the database (no matter which way) it can simply be modified in memory ... (); The entity object is physically updated in the database when the transaction is committed

Entity Management Settings

The <entities> configuration element specifies front end settings that are relevant on the client side and in embedded mode. The default configuration file contains the following <entities> element: <entities> <enhancement agent="true" reflection="warning" /> <cache ref="weak" level2="0mb

Getting Started

ObjectDB is very easy to use. Follow the Getting Started Tutorial and the Quick Tour manual chapter and in minutes you may be able to write and run first Java programs against ObjectDB.

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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