JPA(一)：十分钟入门JPA

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一.JPA的概念

为了节省时间，更加具体的解释我们就略过吧。

二.在IDEA中使用JPA

2.1.添加JAP依赖

添加相关的maven依赖

<properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.7</maven.compiler.source>
        <maven.compiler.target>1.7</maven.compiler.target>
        <hibernate.version>5.2.17.Final</hibernate.version>
        <goda.time.version>2.9.9</goda.time.version>
    </properties>
    <dependencies>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>

        <!-- jdbc驱动包  -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.37</version>
        </dependency>

        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>4.3.10.Final</version>
        </dependency>

        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>4.3.10.Final</version>
        </dependency>

        <dependency>
            <groupId>org.hibernate.javax.persistence</groupId>
            <artifactId>hibernate-jpa-2.1-api</artifactId>
            <version>1.0.0.Final</version>
        </dependency>

        <dependency>
            <groupId>org.hibernate.common</groupId>
            <artifactId>hibernate-commons-annotations</artifactId>
            <version>4.0.5.Final</version>
        </dependency>

        <!--持久化依赖-->
        <dependency>
            <groupId>joda-time</groupId>
            <artifactId>joda-time</artifactId>
            <version>${goda.time.version}</version>
        </dependency>

        <dependency>
            <groupId>org.jadira.usertype</groupId>
            <artifactId>usertype.core</artifactId>
            <version>6.0.1.GA</version>
        </dependency>

        <dependency>
            <groupId>antlr</groupId>
            <artifactId>antlr</artifactId>
            <version>2.7.7</version>
        </dependency>

        <dependency>
            <groupId>dom4j</groupId>
            <artifactId>dom4j</artifactId>
            <version>1.6.1</version>
        </dependency>

        <dependency>
            <groupId>org.jboss</groupId>
            <artifactId>jandex</artifactId>
            <version>1.1.0.Final</version>
        </dependency>

        <dependency>
            <groupId>org.javassist</groupId>
            <artifactId>javassist</artifactId>
            <version>3.18.1-GA</version>
        </dependency>

        <dependency>
            <groupId>org.jboss.logging</groupId>
            <artifactId>jboss-logging</artifactId>
            <version>3.1.4.GA</version>
        </dependency>

        <dependency>
            <groupId>org.jboss.logging</groupId>
            <artifactId>jboss-logging-annotations</artifactId>
            <version>1.2.0.Beta1</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.jboss.spec.javax.transaction</groupId>
            <artifactId>jboss-transaction-api_1.1_spec</artifactId>
            <version>1.0.0.Final</version>
        </dependency>

        <dependency>
            <groupId>javax.ejb</groupId>
            <artifactId>ejb-api</artifactId>
            <version>3.0</version>
        </dependency>

    </dependencies>

2.2.配置JPA运行环境

        在IDEA中，resources文件夹下，也就是资源文件夹下，创建META-INF文件夹，在该文件夹下创建persistence.xml文件，添加以下配置。

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1"
             xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">

    <persistence-unit name="MyJPA" transaction-type="RESOURCE_LOCAL">
        <properties>
            <property name="javax.persistence.jdbc.driver"
                      value="com.mysql.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url"
                      value="jdbc:mysql://localhost:3306/jpa" />
            <property name="javax.persistence.jdbc.user" value="root" />
            <property name="javax.persistence.jdbc.password" value="root" />
            <property name="hibernate.dialect"
                      value="org.hibernate.dialect.MySQL5Dialect" />
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.hbm2ddl.auto" value="update" />
        </properties>

    </persistence-unit>

</persistence>

如下：

2.3.创建表

CREATE TABLE `user` (
    `id` int(11) NOT NULL AUTO_INCREMENT,
    `name` varchar(255) DEFAULT NULL,
    `password` varchar(255) DEFAULT NULL,
   PRIMARY KEY (`id`)
   ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

2.4.在IDEA中配置数据源

在IDEA的右边有Database，按以下步骤操作即可。

这里也可以不配置，配置之后，可以在IDEA中直接看到数据库中的表，并且之后再IDEA中写的代码也不用有警告。

添加你的数据库名字，第一次配置下边会提示你下载插件，很具提示即可。

2.5.测试

创建User类

package com.hly.jpa.model.oneToOne;

import javax.persistence.*;
/**
 * @author :hly
 * @github :github.com/SiriusHly
 * @blog :blog.csdn.net/Sirius_hly
 * @date :2018/9/27
 */
@Entity
//指定表名，指定唯一约束
@Table(name = "user",uniqueConstraints = {@UniqueConstraint(columnNames = {"id","name"})})
public class User {
    @Id//指定主键
    @GeneratedValue
    private int id;
    @Column
    private String name;
    @Column
    private String password;

    //一对一映射
    @OneToOne(optional = true, cascade = CascadeType.ALL)
    @JoinColumn(name = "articleId", unique = true)
    public Article article;

    //省略了getter和setter
}

 /**
     * 获取应用管理的EntityManager
     */
    @Test
    public void testApplicationEntityManager() {
        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("MyJPA");
        EntityManager em = entityManagerFactory.createEntityManager();
        em.getTransaction().begin();
        User user = new User();
        user.setName("hly");
        //以上两行为新建状态
        //托管状态
        em.persist(user);
        //事务提交或调用flush()方法后会同步到数据库
        em.getTransaction().commit();
        //根据主键获取对象
        //System.err.println(em.find(User.class,1));
        //System.err.println(em.getReference(User.class,1));
        em.close();
        entityManagerFactory.close();
    }

数据库中插入数据则成功。

2.6.EntityManager接口

2.7.实体类中注解的含义

2.8.代码及地址思维导图

完整代码在笔者的github,欢迎访问。

清晰思维导图分享地址为：JPA思维导图