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Java EE 7 Essentials by Arun Gupta

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Chapter 13. Java Persistence

The Java Persistence API (JPA) is defined as JSR 338, and the complete specification can be downloaded.

JPA defines an API for the management of persistence and object/relational mapping using a Java domain model.

A database table, typically with multiple columns, stores the persistent state of an application. Multiple rows are stored in the database table to capture different states. A single column or combination of columns may define the uniqueness of each row using primary key constraint. Typically, an application accesses and stores data to multiple tables. These tables generally have relationships defined among them using foreign key constraint.

JPA defines a standard mapping between a database table and a POJO. It defines syntax to capture primary and foreign key constraints and how these rows can be created, read, updated, and deleted using these POJOs. Transactions, caching, validation, and other similar capabilities required by an application accessing a database are also defined by JPA.

This chapter will discuss the key concepts of JPA.

Entities

A POJO with a no-arg public constructor is used to define the mapping with one or more relational database tables. Each such class is annotated with @Entity, and the instance variables that follow JavaBeans-style properties represent the persistent state of the entity. The mapping between the table column and the field name is derived following reasonable defaults and can be overridden by annotations. For ...

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