引出

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1.jpa是啥？java持久层的api，SpringBoot官方支持；
2.约定大于配置的理念，增删改查，save，deleteById，findAll；
3.多条件查询，and，or，like，约定大于配置；
4.多对一的查询，@ManyToOne；

Jpa是啥？

Spring Data JPA

JPA是Java Persistence API的缩写，是Java EE（Enterprise Edition）中用于实现对象关系映射（ORM）的一种规范。它提供了一组用于管理和持久化Java对象的API，使开发人员能够以面向对象的方式操作数据库。

JPA的目标是提供一种统一的、面向对象的数据访问方式，使开发人员能够更加方便地进行数据库操作，而不需要关注底层数据库的细节。它抽象了不同数据库之间的差异，提供了一套通用的API，使开发人员能够以相同的方式操作不同的数据库。

JPA的核心概念包括实体（Entity）、实体管理器（EntityManager）、持久化上下文（Persistence Context）等。开发人员可以通过注解或XML配置来定义实体类和数据库表之间的映射关系，然后使用EntityManager进行增删改查等数据库操作。

JPA的实现有很多，比较常用的有Hibernate、EclipseLink等。开发人员可以根据自己的需求选择合适的JPA实现框架来使用。

Jpa的使用

创建实体类

javax

• @Entity

  @Table

  • @Id
  • @GeneratedValue(strategy) AUTO/IDENTITY(数据库自己的主键自增长策略???)
  • @Column

GenerationType.AUTO:会多一张表，记录键
GenerationType.IDENTITY:用数据库自增的主键
@GeneratedValue(strategy = GenerationType.IDENTITY) // 用数据库自增长策略

在jpa中，ddl-auto共分为四种:

spring.jpa.hibernate.ddl-auto = create ----每次启动SpringBoot程序时，没有表会新建表格，表内有数据会清空；

spring.jpa.hibernate.ddl-auto = create-drop ----每次启动SpringBoot程序时，会清空表数据；

spring.jpa.hibernate.ddl-auto = update ---- 每次启动SpringBoot程序时，没有表格会新建表格，表内有数据不会清空，只会更新；

spring.jpa.hibernate.ddl-auto = validate ---- 每次启动SpringBoot程序时，会校验实体类字段与数据库字段的类型是否相同，不同则会报错；

package com.tianju.jpa.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import javax.persistence.*;
import java.math.BigDecimal;@Data
@NoArgsConstructor
@AllArgsConstructor// 表示这个实体类是和数据库表对应的
@Entity
@Table(name = "car_tab") // 对应的表名
public class Car {@Id // 是主键// GenerationType.AUTO:会多一张表，记录键// GenerationType.IDENTITY:用数据库自增的主键@GeneratedValue(strategy = GenerationType.IDENTITY) // 用数据库自增的策略@Column(name = "car_id")private Integer id;@Column(name = "car_num")private String carNum; // 车牌@Column(name = "car_brand")private String brand; // 品牌@Column(name = "car_color")private String color; // 颜色@Column(name = "car_price")private BigDecimal price; // 价格
}

写dao接口类

JpaRepository<Identity,String>：实体类以及主键的类型

package com.tianju.jpa.mapper;import com.tianju.jpa.entity.Car;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;/*** JpaRepository<Identity,String>：实体类以及主键的类型*/
@Repository // 用在持久化对象上，类似于mapper
public interface CarDao extends JpaRepository<Car,Integer> {
}

写服务类

package com.tianju.jpa.service.impl;import com.tianju.jpa.entity.Car;
import com.tianju.jpa.mapper.CarDao;
import com.tianju.jpa.service.ICarService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;@Service
public class CarServiceImpl implements ICarService {@Autowiredprivate CarDao carDao;@Overridepublic void add(Car car) {carDao.save(car);}
}

crud增删改查

增加

carDao.save(car);

插入多条数据

插入后的结果

修改

    @Overridepublic void update(Car car) {carDao.save(car);}@Overridepublic Car findById(int id) {Car car = carDao.findById(id).get();return car;}

根据id删除

    @Overridepublic void deleteById(int id) {carDao.deleteById(id);}

全查询

    @Overridepublic List<Car> findAll() {return carDao.findAll();}

分页查询

import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;

    @Overridepublic Page findByPage(int pageNum, int pageSize) {PageRequest pageRequest = PageRequest.of(pageNum, pageSize);Page<Car> carPage = carDao.findAll(pageRequest);return carPage;}

分页查询的sql

条件查询模糊查询

单条件查询

package com.tianju.jpa.mapper;import com.tianju.jpa.entity.Car;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;import java.util.List;/*** JpaRepository<Identity,String>：实体类以及主键的类型*/
@Repository // 用在持久化对象上，类似于mapper
public interface CarDao extends JpaRepository<Car,Integer> {List<Car> findCarsByColor(String color);
}

多条件查询

package com.tianju.jpa.mapper;import com.tianju.jpa.entity.Car;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;import java.util.List;/*** JpaRepository<Identity,String>：实体类以及主键的类型*/
@Repository // 用在持久化对象上，类似于mapper
public interface CarDao extends JpaRepository<Car,Integer> {List<Car> findCarsByColor(String color);List<Car> findByColorAndBrand(String color,String brand);List<Car> findByColorOrBrand(String color,String brand);}

or查询

模糊查询

package com.tianju.jpa.mapper;import com.tianju.jpa.entity.Car;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;import java.util.List;/*** JpaRepository<Identity,String>：实体类以及主键的类型*/
@Repository // 用在持久化对象上，类似于mapper
public interface CarDao extends JpaRepository<Car,Integer> {List<Car> findCarsByColor(String color);List<Car> findByColorAndBrand(String color,String brand);List<Car> findByColorOrBrand(String color,String brand);List<Car> findByBrandLike(String brand);}

排序查询

package com.tianju.jpa.service.impl;import com.tianju.jpa.entity.Car;
import com.tianju.jpa.mapper.CarDao;
import com.tianju.jpa.service.ICarService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Service;import java.util.List;@Service
public class CarServiceImpl implements ICarService {@Autowiredprivate CarDao carDao;@Overridepublic void add(Car car) {carDao.save(car);}@Overridepublic void update(Car car) {carDao.save(car);}@Overridepublic Car findById(int id) {Car car = carDao.findById(id).get();return car;}@Overridepublic void deleteById(int id) {carDao.deleteById(id);}@Overridepublic List<Car> findAll() {return carDao.findAll();}@Overridepublic Page findByPage(int pageNum, int pageSize) {PageRequest pageRequest = PageRequest.of(pageNum, pageSize);Page<Car> carPage = carDao.findAll(pageRequest);return carPage;}@Overridepublic List<Car> findCarsByColor(String color) {return carDao.findCarsByColor(color);}@Overridepublic List<Car> findByColorAndBrand(String color, String brand) {return carDao.findByColorAndBrand(color, brand);}@Overridepublic List<Car> findByColorOrBrand(String color, String brand) {return carDao.findByColorOrBrand(color,brand);}@Overridepublic List<Car> findByBrandLike(String brand) {return carDao.findByBrandLike(brand);}@Overridepublic List<Car> orderByPrice() {Sort price = Sort.by(Sort.Direction.DESC, "price");return carDao.findAll(price);}
}

多对一查询

定义实体类

package com.tianju.jpa.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import javax.persistence.*;
import java.math.BigDecimal;@Data
@NoArgsConstructor
@AllArgsConstructor// 表示这个实体类是和数据库表对应的
@Entity
@Table(name = "car_tab") // 对应的表名
public class Car {@Id // 是主键// GenerationType.AUTO:会多一张表，记录键// GenerationType.IDENTITY:用数据库自增的主键@GeneratedValue(strategy = GenerationType.IDENTITY) // 用数据库自增的策略@Column(name = "car_id")private Integer id;@Column(name = "car_num")private String carNum; // 车牌@Column(name = "car_brand")private String brand; // 品牌@Column(name = "car_color")private String color; // 颜色@Column(name = "car_price")private BigDecimal price; // 价格@ManyToOne@JoinColumn(name = "factory_id")private Factory factory; // 多对一的工厂
}

package com.tianju.jpa.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import javax.persistence.*;/*** 生产车的工厂，多个车对应一个工厂*/@Data
@NoArgsConstructor
@AllArgsConstructor// 表示这个实体类是和数据库表对应的
@Entity
@Table(name = "car_factory") // 对应的表名public class Factory {@Id@GeneratedValue(strategy = GenerationType.AUTO)@Column(name = "factory_id")private Integer id;@Column(name = "factory_name")private String name;}

自动建的表

auto主键策略下新增

新增后的表

进行全查询测试

运行的SQL语句

全部代码

application.yml配置类

在jpa中，ddl-auto共分为四种:

spring.jpa.hibernate.ddl-auto = create ----每次启动SpringBoot程序时，没有表会新建表格，表内有数据会清空；

spring.jpa.hibernate.ddl-auto = create-drop ----每次启动SpringBoot程序时，会清空表数据；

spring.jpa.hibernate.ddl-auto = update ---- 每次启动SpringBoot程序时，没有表格会新建表格，表内有数据不会清空，只会更新；

spring.jpa.hibernate.ddl-auto = validate ---- 每次启动SpringBoot程序时，会校验实体类字段与数据库字段的类型是否相同，不同则会报错；

spring:datasource:driver-class-name: com.mysql.cj.jdbc.Driverurl: jdbc:mysql://192.168.111.130:3306/jpa_db?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2B8&allowMultiQueries=trueusername: rootpassword: 123jpa:# 允许显示sqlshow-sql: truehibernate:# 自动对表进行增删改查的操作，创建表# 可以开始的时候打开，等表创建好之后关闭ddl-auto: updateserver:port: 9089

pom配置文件

<?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><groupId>com.tianju.jpa</groupId><artifactId>spring-boot-jpa</artifactId><version>1.0-SNAPSHOT</version><properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><!--    起步依赖--><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.6.13</version></parent><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version><scope>test</scope></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><!--mysql驱动--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><scope>runtime</scope></dependency><dependency><groupId>com.github.xiaoymin</groupId><artifactId>knife4j-openapi2-spring-boot-starter</artifactId><version>4.0.0</version></dependency><!--        Jpa的包--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId></dependency></dependencies></project>

实体类

Car实体类

package com.tianju.jpa.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import javax.persistence.*;
import java.math.BigDecimal;@Data
@NoArgsConstructor
@AllArgsConstructor// 表示这个实体类是和数据库表对应的
@Entity
@Table(name = "car_tab") // 对应的表名
public class Car {@Id // 是主键// GenerationType.AUTO:会多一张表，记录键// GenerationType.IDENTITY:用数据库自增的主键@GeneratedValue(strategy = GenerationType.IDENTITY) // 用数据库自增的策略@Column(name = "car_id")private Integer id;@Column(name = "car_num")private String carNum; // 车牌@Column(name = "car_brand")private String brand; // 品牌@Column(name = "car_color")private String color; // 颜色@Column(name = "car_price")private BigDecimal price; // 价格@ManyToOne@JoinColumn(name = "factory_id")private Factory factory; // 多对一的工厂
}

Factory实体类

package com.tianju.jpa.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import javax.persistence.*;/*** 生产车的工厂，多个车对应一个工厂*/@Data
@NoArgsConstructor
@AllArgsConstructor// 表示这个实体类是和数据库表对应的
@Entity
@Table(name = "car_factory") // 对应的表名public class Factory {@Id@GeneratedValue(strategy = GenerationType.AUTO)@Column(name = "factory_id")private Integer id;@Column(name = "factory_name")private String name;}

dao接口类

package com.tianju.jpa.mapper;import com.tianju.jpa.entity.Car;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;import java.util.List;/*** JpaRepository<Identity,String>：实体类以及主键的类型*/
@Repository // 用在持久化对象上，类似于mapper
public interface CarDao extends JpaRepository<Car,Integer> {List<Car> findCarsByColor(String color);List<Car> findByColorAndBrand(String color,String brand);List<Car> findByColorOrBrand(String color,String brand);List<Car> findByBrandLike(String brand);}

service服务类

package com.tianju.jpa.service.impl;import com.tianju.jpa.entity.Car;
import com.tianju.jpa.mapper.CarDao;
import com.tianju.jpa.service.ICarService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Service;import java.util.List;@Service
public class CarServiceImpl implements ICarService {@Autowiredprivate CarDao carDao;@Overridepublic void add(Car car) {carDao.save(car);}@Overridepublic void update(Car car) {carDao.save(car);}@Overridepublic Car findById(int id) {Car car = carDao.findById(id).get();return car;}@Overridepublic void deleteById(int id) {carDao.deleteById(id);}@Overridepublic List<Car> findAll() {return carDao.findAll();}@Overridepublic Page findByPage(int pageNum, int pageSize) {PageRequest pageRequest = PageRequest.of(pageNum, pageSize);Page<Car> carPage = carDao.findAll(pageRequest);return carPage;}@Overridepublic List<Car> findCarsByColor(String color) {return carDao.findCarsByColor(color);}@Overridepublic List<Car> findByColorAndBrand(String color, String brand) {return carDao.findByColorAndBrand(color, brand);}@Overridepublic List<Car> findByColorOrBrand(String color, String brand) {return carDao.findByColorOrBrand(color,brand);}@Overridepublic List<Car> findByBrandLike(String brand) {return carDao.findByBrandLike(brand);}@Overridepublic List<Car> orderByPrice() {Sort price = Sort.by(Sort.Direction.DESC, "price");return carDao.findAll(price);}
}

测试代码

package com.tianju.jpa.mapper;import com.tianju.jpa.entity.Car;
import com.tianju.jpa.entity.Factory;
import com.tianju.jpa.service.ICarService;
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.data.domain.Page;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;import java.math.BigDecimal;
import java.util.List;
import java.util.Random;import static org.junit.Assert.*;@SpringBootTest
@RunWith(SpringJUnit4ClassRunner.class)
public class CarDaoTest {@Autowiredprivate ICarService carService;@Testpublic void addCar(){for (int i =0;i<10;i++){double random = Math.round(Math.random() * 100) / 100.0 + 8888;
//            carService.add(new Car(null,"苏A888" +i,"BMW","红色",new BigDecimal(random)));}}@Testpublic void updateCar(){Car car = carService.findById(10);car.setCarNum("浙江888");carService.update(car);}@Autowiredprivate FactoryDao factoryDao;@Testpublic void addFactory(){factoryDao.save(new Factory(null,"上海工厂"));factoryDao.save(new Factory(null,"南京工厂"));factoryDao.save(new Factory(null,"山西工厂"));}@Testpublic void deleteById(){carService.deleteById(11);}@Testpublic void findCarsByColor(){List<Car> cars = carService.findCarsByColor("红色");cars.forEach(System.out::println);}@Testpublic void findCarsByColorAndBrand(){List<Car> cars = carService.findByColorAndBrand("红色","BYD");cars.forEach(System.out::println);}@Testpublic void findCarsByColorOrBrand(){List<Car> cars = carService.findByColorOrBrand("红色","BYD");cars.forEach(System.out::println);}@Testpublic void findByPage(){Page page = carService.findByPage(1, 3);page.forEach(car -> {System.out.println(car);});}@Testpublic void findAll(){List<Car> all = carService.findAll();all.forEach(car -> {System.out.println(car);});}@Testpublic void findLike(){List<Car> all = carService.findByBrandLike("B"+"%");all.forEach(car -> {System.out.println(car);});}@Testpublic void orderByPrice(){List<Car> all = carService.orderByPrice();all.forEach(car -> {System.out.println(car);});}public static void main(String[] args) {double random = Math.round(Math.random() * 100) / 100.0;System.out.println(random);}}

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总结

1.jpa是啥？java持久层的api，SpringBoot官方支持；
2.约定大于配置的理念，增删改查，save，deleteById，findAll；
3.多条件查询，and，or，like，约定大于配置；
4.多对一的查询，@ManyToOne；