JPA入门教程：Java ORM标准化利器

需积分: 16 123 浏览量更新于2024-07-19 收藏 3.16MB PDF 举报

本篇教程是关于Java Persistence API (JPA)的简单介绍，它是Java EE 5.0平台的一项重要标准，旨在解决ORM（对象关系映射）领域的问题，吸取了EJB规范的经验教训，提供了易于使用且具有强大扩展性的持久化解决方案。JPA的目标是成为ORM领域的整合者，凭借其设计，已经赢得了开发社区的广泛关注和好评。该教程主要面向那些从事Java编程并需要与数据库交互的开发者，特别是那些对JDBC有一定理解的程序员。通过学习，读者将能够掌握如何利用JPA将数据库对象存储到内存中的基本操作。教程的前提是读者需具备Java 1.6或更高版本的基本编程知识，以及对JDBC概念的理解。值得注意的是，本教程由TutorialsPoint (I) Pvt. Ltd.发布，版权属于该公司，未经书面许可，禁止以任何形式复制、分发或再版本教程的任何内容。虽然TutorialsPoint努力保持网站和教程内容的及时性和准确性，但可能仍存在信息不准确或错误的情况。用户在参考时应自行核实，并理解使用本教程可能存在一定的风险。本JPA教程是一个实用的入门指南，不仅涵盖了JPA的核心概念，还帮助开发者建立起使用JPA进行数据持久化的坚实基础，对于提高Java开发人员的数据库操作效率和质量具有重要意义。随着JPA在现代企业应用中的广泛应用，学习和掌握这一技术将成为开发者必备的技能之一。

JAVA PERSISTENCE API (JPA)

{

return deg;

}

public void setDeg(String deg)

{

this.deg = deg;

}

The above code is the Employee entity POJO class. It contain four attributes eid,

ename, salary, and deg. Consider these attributes as the table fields in a table and eid

as the primary key of this table. Now we have to design the hibernate mapping file for it.

The mapping file named mapping.xml is as follows:

<? xml version="1.0" encoding="UTF-8" ?>

<entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm

http://java.sun.com/xml/ns/persistence/orm_1_0.xsd"

version="1.0">

<description> XML Mapping file</description>

<generated-value strategy="TABLE"/>

</id>

</basic>

</basic>

</basic>

</attributes>

</entity>

</entity-mappings>

JAVA PERSISTENCE API (JPA)

The above script is used for mapping the entity class with the database table. In this file,

 <entity-mappings> tag defines the schema definition to allow entity tags into the

xml file.

 <description> tag provides a description of the application.

 <entity> tag defines the entity class which you want to convert into a table in a

database. Attribute class defines the POJO entity class name.

 <table> tag defines the table name. If you want to have identical names for both

the class as well as the table, then this tag is not necessary.

 <attributes> tag defines the attributes (fields in a table).

 <id> tag defines the primary key of the table. The <generated-value> tag

defines how to assign the primary key value such as Automatic, Manual, or Taken

from Sequence.

 <basic> tag is used for defining the remaining attributes of the table.

 <column-name> tag is used to set user-defined field names in the table.

Annotations

Generally xml files are used to configure specific components, or mapping two different

specifications of components. In our case, we have to maintain xml files separately in a

framework. That means while writing a mapping xml file, we need to compare the POJO

class attributes with entity tags in the mapping.xml file.

Here is the solution. In the class definition, we can write the configuration part using

annotations. Annotations are used for classes, properties, and methods. Annotations

start with ‘@’ symbol. Annotations are declared prior to a class, property, or method. All

annotations of JPA are defined in the javax.persistence package.

The list of annotations used in our examples are given below.

Annotation

Description

@Entity

Declares the class as an entity or a table.

@Table

Declares table name.

@Basic

Specifies non-constraint fields explicitly.

@Embedded

Specifies the properties of class or an entity whose

value is an instance of an embeddable class.

剩余112页未读，继续阅读

m0_37710887

粉丝: 0
资源: 1

JPA入门教程：Java ORM标准化利器

spring data jpa视频教程

JPA使用教程

jpa的工程

springdatajpa使用教程

jparepository使用教程

给我一个简单的springboot+jpa+mysql8.0的表单增删改查的教程

springboot jpa 多对多 增删改

Springboot教程

javaee实用教程第三版郑阿奇源代码

springboot项目教程

最新资源

springboot jpa 多对多增删改