前言

简单基础入门级别，有基础勿留香！

一、新建一个空boot项目

傻瓜式创建即可

二、准备好数据库，下面以MySQL为主

创建好测试表dog表，待用

三、导入依赖

在这里插入图片描述

下面依赖，后续会用到，直接贴上了

<!--本demo 核心依赖 begin-->
 <dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-web</artifactId>
 </dependency>
 <dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-data-jpa</artifactId>
 </dependency>

 <dependency>
     <groupId>mysql</groupId>
     <artifactId>mysql-connector-java</artifactId>
     <scope>runtime</scope>
 </dependency>

 <dependency>
     <groupId>org.projectlombok</groupId>
     <artifactId>lombok</artifactId>
     <version>1.16.14</version>
 </dependency>
 <dependency>
     <groupId>com.alibaba</groupId>
     <artifactId>fastjson</artifactId>
     <version>1.2.76</version>
 </dependency>
 <!--本demo 核心依赖 end-->

四、生成JPA实体

JPA自动生成 JPA 实体类（idea）.

五、JPA基本注解

@entity
@Table(name=“table_name”)
当前实体与其映射的数据库表名不同时需要加此注解，如果一致，不加也行
@Id 主键
@GeneratedValue
主键的生成策略，例：@GeneratedValue(strategy = GenerationType.AUTO)
@Basic
表示一个简单的属性到数据库表的字段的映射，对于没有任何标注的getXXX()方法，默认即为@basic，会把XXX映射为数据库的一列
即：如果在实体的get方法上没加注解，则默认加了@Basic（此注解加不加都行）
@Column(name = “dog_name”) 映射数据库字段名
@Transient 表示该属性并非一个到数据库表的字段的映射，ORM框架将忽略该属性，如果一个属性并非数据库表的字段的映射，就务必将其标示为@Transient，否则，ORM框架默认其注解为@basic
@Temporal(TemporalType.DATE)
在进行属性映射时可使用此注解来调整数据库存储日期的精度（通过设置：TemporalType.DATE，TemporalType.TIMESTAMP）

六、JPQL 和 EntityManager

在这里插入图片描述

简单入门代码如下：
实体：JPA自动生成的

package com.liu.susu.pojo;

import javax.persistence.*;
import java.util.Objects;

@NamedQuery(name = "testNamedQuery",query = "select d from com.liu.susu.pojo.Dog d")
@Entity
public class Dog {
    private int dogNum;
    private String dogName;
    private String dogKind;
    private Integer dogAge;
    private String decision;


    public Dog(){

    }

    public Dog(int dogNum, String dogName) {
        this.dogNum = dogNum;
        this.dogName = dogName;
    }

    @Id
    @Column(name = "dog_num")
    public int getDogNum() {
        return dogNum;
    }

    public void setDogNum(int dogNum) {
        this.dogNum = dogNum;
    }

    @Basic
    @Column(name = "dog_name")
    public String getDogName() {
        return dogName;
    }

    public void setDogName(String dogName) {
        this.dogName = dogName;
    }

    @Basic
    @Column(name = "dog_kind")
    public String getDogKind() {
        return dogKind;
    }

    public void setDogKind(String dogKind) {
        this.dogKind = dogKind;
    }

    @Basic
    @Column(name = "dog_age")
    public Integer getDogAge() {
        return dogAge;
    }

    public void setDogAge(Integer dogAge) {
        this.dogAge = dogAge;
    }

    @Basic
    @Column(name = "decision")
    public String getDecision() {
        return decision;
    }

    public void setDecision(String decision) {
        this.decision = decision;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Dog dog = (Dog) o;
        return dogNum == dog.dogNum && Objects.equals(dogName, dog.dogName) && Objects.equals(dogKind, dog.dogKind) && Objects.equals(dogAge, dog.dogAge) && Objects.equals(decision, dog.decision);
    }

    @Override
    public int hashCode() {
        return Objects.hash(dogNum, dogName, dogKind, dogAge, decision);
    }
}

两个dao

package com.liu.susu.dao;

import com.liu.susu.pojo.Dog;
import org.springframework.data.jpa.repository.JpaRepository;

public interface DogDao extends JpaRepository<Dog,Integer> {

}

package com.liu.susu.dao;

import com.liu.susu.pojo.Dog;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;

import java.util.List;

/**
 * jpql查询
 */
public interface DogDao2 extends JpaRepository<Dog,Integer> {
    /**
     * 没有限制条件的查所有
     * @return
     */
    @Query(value = "from com.liu.susu.pojo.Dog")
    List<Dog> getDogList();

    /**
     * 给个别名d，类似查询select *
     * @return
     */
    @Query(value = "select d from com.liu.susu.pojo.Dog d")
    List<Dog> getDogList2();

    /**
     * 这种写法，查具体字段的,查询结果集并没有封装到实体对象中，
     *         而是封装到了Object[]中
     * @return
     */
    @Query(value = "select dogNum,dogName from com.liu.susu.pojo.Dog d")
    List<Object[]> getDogObjectList();

    /**
     * new 一个，所以查询结果直接封装到了对应的实体里，但是需要对应的构造器
     *          所以如果查的字段多的话，就比较麻烦·
     * @return
     */
    @Query(value = "select new com.liu.susu.pojo.Dog(dogNum,dogName) from com.liu.susu.pojo.Dog d")
    List<Dog> getDogList3();

    /**
     * 根据条件查询
     * @return
     */
    @Query(value = "select d from com.liu.susu.pojo.Dog d where d.dogAge=?1")
    List<Dog> getDogList0(int dogAge);


}

4个controller

package com.liu.susu.controller;

import com.alibaba.fastjson.JSONObject;
import com.liu.susu.dao.DogDao;
import com.liu.susu.pojo.Dog;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import java.util.List;

@Controller
@RequestMapping("/dog/dao1")
public class DogDaoController {

    @Autowired
    private DogDao dogDao;

    /**
     * 查询所有
     * @return
     */
    @ResponseBody
    @RequestMapping("/all")
    public String testFindAll(){
        List<Dog> dogList = dogDao.findAll();
        return JSONObject.toJSONString(dogList);
    }
    /**
     * 查询所有 并 根据dogAge字段进行排序
     * @return
     */
    @ResponseBody
    @RequestMapping("/all2")
    public List<Dog> testFindAll2(){
//        List<Dog> dogList = dogDao.findAll(Sort.by("dogAge"));//默认升序
        List<Dog> dogList = dogDao.findAll(Sort.by("dogAge").descending());
        return dogList;
    }
    /**
     * 查询所有 并 根据dogAge字段进行排序
     * @return
     */
    @ResponseBody
    @RequestMapping("/save")
    public List<Dog> testSave(){
        Dog dog = new Dog();
        dog.setDogNum(1005);//主键要加
        dog.setDogName("酥妮");
        dog.setDogAge(1);
        dogDao.save(dog);//保存新增
        List<Dog> dogList = dogDao.findAll();
        return dogList;
    }

}

package com.liu.susu.controller;

import com.liu.susu.dao.DogDao2;
import com.liu.susu.pojo.Dog;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import java.util.List;


@Controller
@RequestMapping("/dog/dao2")
public class DogDao2Controller {
    @Autowired
    private DogDao2 dogDao2;

    @ResponseBody
    @RequestMapping("/list")
    private List<Dog> getDogList(){
        List<Dog> dogList = dogDao2.getDogList();
        return dogList;
    }
    @ResponseBody
    @RequestMapping("/list2")
    private List<Dog> getDogList2(){
        List<Dog> dogList = dogDao2.getDogList2();
        return dogList;
    }
    @ResponseBody
    @RequestMapping("/objList")
    private List<Object[]> getDogObjectList(){
        List<Object[]> dogObjectList = dogDao2.getDogObjectList();
        return dogObjectList;
    }
    @ResponseBody
    @RequestMapping("/list3")
    private List<Dog> getDogList3(){
        List<Dog> dogList = dogDao2.getDogList3();
        return dogList;
    }
    /**
     * 根据条件查询
     * @param dogAge
     * @return
     */
    @ResponseBody
    @RequestMapping("/listByDogAge")
    private List<Dog> getDogListByParam(@RequestParam int dogAge){
        List<Dog> dogList = dogDao2.getDogList0(dogAge);
        return dogList;
    }

}

package com.liu.susu.controller;

import com.liu.susu.pojo.Dog;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;
import javax.transaction.Transactional;
import java.util.List;

@Controller
@RequestMapping("/dog/entityManager1")
public class EntityManagerController {

    @PersistenceContext
    private EntityManager entityManager;

    @ResponseBody
    @RequestMapping("/list1")
    public List<Dog> getDogList(){
        String sql = "select * from dog";
        List<Dog> dogList = entityManager.createNativeQuery(sql)
                .getResultList();//结果只有属性值，没有属性名
        return dogList;
    }
    @ResponseBody
    @RequestMapping("/list2")
    public List<Dog> getDogList2(){
        String sql = "select * from dog";
        List<Dog> dogList = entityManager.createNativeQuery(sql,Dog.class)
                .getResultList();//结果===>有属性名
        return dogList;
    }
    /**
     * sql注入
     *    通过参数查询
     * @param dogNum
     * @return
     */
    @ResponseBody
    @RequestMapping("/dog1")
    public Dog getDogByNum(@RequestParam Integer dogNum){
        String sql = "select * from dog d where d.dog_num=?1";
        Query query = entityManager.createNativeQuery(sql,Dog.class);
        query.setParameter(1,dogNum);
        Dog dog = (Dog) query.getSingleResult();
        return dog;
    }
    @ResponseBody
    @RequestMapping("/save")
    @Transactional()//事务注解 记得加
    public String testPersist(){
        Dog dog = new Dog();
        dog.setDogNum(1006);
        dog.setDogName("测试");
        dog.setDogAge(0);
        entityManager.persist(dog);//直接insert
        return "ok";
    }
    @ResponseBody
    @RequestMapping("/merge")
    @Transactional()//事务注解 记得加
    public String testMerge(){
        Dog dog = new Dog();
        dog.setDogNum(1006);
        dog.setDogName("测试2");
        dog.setDogAge(0);
        entityManager.merge(dog);//内部原理：先根据主键查询再update
        return "ok";
    }

}

package com.liu.susu.controller;

import com.liu.susu.pojo.Dog;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import java.util.List;

@Controller
@RequestMapping("/dog/jpqlAndEntityManager")
public class JpqlAndEntityManagerController {

    @PersistenceContext
    private EntityManager entityManager;

    @ResponseBody
    @RequestMapping("/list1")
    public List<Dog> getDogList(){
        List<Dog> dogList = entityManager.createNamedQuery("testNamedQuery")
                .getResultList();
        return dogList;
    }

}

七、配置文件

配置

server.port=8993
# 应用名称
spring.application.name=springboot-jpa
# 数据库驱动：
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
# 数据库连接地址
spring.datasource.url=jdbc:mysql://localhost:3306/liu?serverTimezone=UTC
# 数据库用户名&密码：
spring.datasource.username=root
spring.datasource.password=root

#spring.jpa.generate-ddl=true
#spring.jpa.hibernate.ddl-auto=validate
spring.jpa.show-sql=true
# 指定数据库得类型
spring.jpa.database-platform=org.hibernate.dialect.MySQL57InnoDBDialect

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.liu.susu</groupId>
    <artifactId>springboot-jpa</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springboot-jpa</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <spring-boot.version>2.3.2.RELEASE</spring-boot.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

        <!--本demo 核心依赖 begin-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.16.14</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.76</version>
        </dependency>
        <!--本demo 核心依赖 end-->

    </dependencies>


    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>${spring-boot.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.3.7.RELEASE</version>
                <configuration>
                    <mainClass>com.liu.susu.SpringbootJpaApplication</mainClass>
                </configuration>
                <executions>
                    <execution>
                        <id>repackage</id>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>