Spring Boot Jpa

全称Java Persistence API，通过JDK 5.0注解或XML描述对象－关系表的映射关系，并将运行期的实体对象持久化到数据库中。

​ JPA的出现有两个原因：
其一，简化现有Java EE和Java SE应用的对象持久化的开发工作；
其二，Sun希望整合对ORM技术，实现持久化领域的统一。

​ JPA提供的技术：

1）ORM映射元数据：JPA支持XML和JDK 5.0注解两种元数据的形式，元数据描述对象和表之间的映射关系，框架据此将实体对象持久化到数据库表中；

2）JPA 的API：用来操作实体对象，执行CRUD操作，框架在后台替我们完成所有的事情，开发者从繁琐的JDBC和SQL代码中解脱出来。

3）查询语言：通过面向对象而非面向数据库的查询语言查询数据，避免程序的SQL语句紧密耦合。

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pom.xml中导入依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>2.1.3.RELEASE</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.caicai</groupId>
   <artifactId>spring-boot-jpa</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>spring-boot-jpa</name>
   <description>Demo project for Spring Boot</description>

   <properties>
      <java.version>1.8</java.version>
   </properties>

   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-data-jpa</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-jdbc</artifactId>
      </dependency>

      <dependency>
         <groupId>mysql</groupId>
         <artifactId>mysql-connector-java</artifactId>
         <scope>runtime</scope>
      </dependency>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
      </dependency>
   </dependencies>

   <build>
      <plugins>
         <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
         </plugin>
      </plugins>
   </build>

</project>

创建实体类

package com.caicai.springbootjpa.entity;

import javax.persistence.*;

/**
 * @author liu
 * @title: User
 * @projectName spring-boot-jpa
 * @description: TODO
 * @date 2019/3/3121:14
 */

@Entity
public class User {
    @GeneratedValue(strategy = GenerationType.AUTO)//设置自增长策略
    @Id
    private Integer id;
    @Column(length = 20,nullable = false)  //column可以设置属性
    private String name;
    @Column(length = 20,nullable = true)
    private Integer age;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public User() {
    }

    public User(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
}

创建UserRepository

package com.caicai.springbootjpa.repository;

import com.caicai.springbootjpa.entity.User;
import org.springframework.data.jpa.repository.JpaRepository;

/**
 * @author liu
 * @title: UserRepository
 * @projectName spring-boot-jpa
 * @description: TODO
 * @date 2019/3/3121:06
 */
public interface UserRepository extends JpaRepository<User,Integer>{
}

配置数据源和自动建表:

spring:
  datasource:
    username: root
    password: 123456
    url: jdbc:mysql://localhost:3306/jpa
    driver-class-name: com.mysql.jdbc.Driver
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true

测试类:

package com.caicai.springbootjpa;

import com.caicai.springbootjpa.entity.User;
import com.caicai.springbootjpa.repository.UserRepository;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringBootJpaApplicationTests {
    @Autowired
    UserRepository userRepository;
	@Test
	public void test() {
	    User user = new User();
	    user.setAge(10);
	    user.setName("caicai");
	    userRepository.save(user);
	}

}