JPA学习之注解总结篇

比眉伴天荒 2021-09-07 06:12 340阅读 0赞

### 前言： ###

> 现在直接操作数据库广泛使用的就是Mybatis和JPA.两种技术都是很好用的，但是相信使用过JPA的人都很清楚，jpa比较mybatis而言，无论是自动创建表单还是可直接调用的操作数据库的方法，都是mybatis所没有的。
> 
> 在网上看到不少前辈的文章，本文不在做过多的JPA相关讲解，着重于JPA的应用。JPA的参考资料以及学习视频已经在本篇文章的第二部分给出相关链接。

### 一、什么是JPA ###

JPA是Java Persistence API的简称，中文名Java持久层API，是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][Link 1]到数据库中。

### 二、JPA的参考资料 ###

>  *  spring boot 中使用 jpa以及jpa介绍：https://blog.csdn.net/wujiaqi0921/article/details/78789087
>  *  JPA之常用 基本注解：https://www.cnblogs.com/a8457013/p/7753575.html
>  *  JPA @Basic 注解：http://fanlychie.github.io/post/jpa-basic-annotation.html
>  *  JPA的Basic注解：http://www.voidcn.com/article/p-ficnnwzf-bbe.html
>  *  Hibernate，JPA注解@EmbeddedId：https://www.cnblogs.com/xiluhua/p/4382062.html
>  *  JPA实体标识的自动生成@ SequenceGenerator @GeneratedValue：https://blog.csdn.net/langjian2012/article/details/38894195
>  *  【JPA】对象关系映射\_访问模式（ACCESS\_TYPE(field|Property)）：https://blog.csdn.net/jinghua7/article/details/21455727
>  *  JPA官网：https://blog.csdn.net/weixin\_41244495/article/details/88384799
>  *  JPA、Hibernate、Spring data jpa之间的关系，终于明白了：https://my.oschina.net/u/3080373/blog/1828589
>  *  JPA中@Access注解小结：https://my.oschina.net/u/1156626/blog/1619239?utm\_medium=referral
>  *  JPA中@JoinTable和@JoinColumn注解的使用：https://blog.csdn.net/yu870646595/article/details/51064634
>  *  JPA 唯一约束条件@UniqueConstraint注解在Oracle失效问题（数据库表名字段名长度问题）：https://blog.csdn.net/weixin\_42142057/article/details/100573260
>  *  JPA注解添加唯一约束：https://blog.csdn.net/qq\_38705025/article/details/86636818
>  *  Java中的@UniqueConstraint注释：https://www.javaroad.cn/articles/1265
>  *  视频：https://www.bilibili.com/video/BV1hE411s72B?from=search&seid=6182882383637815756

### 三、JPA的应用 ###

3.1 项目结构

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1RoZV9CZXN0X0hhY2tlcg_size_16_color_FFFFFF_t_70][]

3.2 pom.xml以及application.properties

<?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>
        <parent>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>2.4.3</version>
            <relativePath/> 
        </parent>
        <groupId>com.example</groupId>
        <artifactId>jpa_study</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <name>jpa_study</name>
        <description>Demo project for Spring Boot</description>
        <properties>
            <java.version>11</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-web</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.postgresql</groupId>
                <artifactId>postgresql</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>

server.port=8989
    spring.datasource.platform=postgres
    spring.datasource.url=jdbc:postgresql://127.0.0.1:5432/student
    spring.datasource.username=postgres
    spring.datasource.password=root
    spring.datasource.driverClassName=org.postgresql.Driver
    
    spring.jpa.show-sql=true
    spring.jpa.hibernate.ddl-auto=update
    spring.jpa.properties.hibernate.temp.use_jdbc_metadata_defaults=false
    spring.jpa.database-platform=org.hibernate.dialect.PostgreSQL9Dialect
    spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect

3.3 实体类

package com.example.jpa_study.controller.param;
    
    public class StudentParam {
        private String name;
        private String address;
        private Integer pageNo;
        private Integer pageSize;
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getAddress() {
            return address;
        }
    
        public void setAddress(String address) {
            this.address = address;
        }
    
        public Integer getPageNo() {
            return pageNo;
        }
    
        public void setPageNo(Integer pageNo) {
            this.pageNo = pageNo;
        }
    
        public Integer getPageSize() {
            return pageSize;
        }
    
        public void setPageSize(Integer pageSize) {
            this.pageSize = pageSize;
        }
    }

package com.example.jpa_study.controller.vo;
    
    import java.util.List;
    
    public class PageData<T> {
        private List<T> list;
        private long total;
    
        public List<T> getList() {
            return list;
        }
    
        public void setList(List<T> list) {
            this.list = list;
        }
    
        public long getTotal() {
            return total;
        }
    
        public void setTotal(long total) {
            this.total = total;
        }
    }

package com.example.jpa_study.repository.entity;
    
    import org.hibernate.annotations.CreationTimestamp;
    import org.hibernate.annotations.GenericGenerator;
    import org.hibernate.annotations.UpdateTimestamp;
    
    import javax.persistence.*;
    import java.util.Date;
    
    @Table(name = "tb_student_info")
    @Entity
    public class Student {
        /**
         * 主键id
         */
        private String id;
        /**
         * 学生姓名
         */
        private String name;
        /**
         * 学生年龄 不放入数据库中
         */
        private Integer age;
        /**
         * 出生年月日
         */
        private Date birthDay;
        /**
         * 家庭住址
         */
        private String address;
        /**
         * 创建时间
         */
        private Date createTime;
        /**
         * 更新时间
         */
        private Date updateTime;
    
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO, generator = "uuid")
        @GenericGenerator(name = "uuid", strategy = "uuid2")
        public String getId() {
            return id;
        }
    
        public void setId(String id) {
            this.id = id;
        }
    
        @Column(name = "stu_name", length = 20, nullable = false)
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        @Transient
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        @Temporal(TemporalType.DATE)
        public Date getBirthDay() {
            return birthDay;
        }
    
        public void setBirthDay(Date birthDay) {
            this.birthDay = birthDay;
        }
    
        public String getAddress() {
            return address;
        }
    
        public void setAddress(String address) {
            this.address = address;
        }
    
        @CreationTimestamp
        @Temporal(TemporalType.TIMESTAMP)
        public Date getCreateTime() {
            if (createTime != null) {
                return (Date) createTime.clone();
            }
            return null;
        }
    
        public void setCreateTime(Date createTime) {
            this.createTime = createTime == null ? null : (Date) createTime.clone();
        }
    
        @UpdateTimestamp
        @Temporal(TemporalType.TIMESTAMP)
        public Date getUpdateTime() {
            if (updateTime != null) {
                return (Date) updateTime.clone();
            }
            return null;
        }
    
        public void setUpdateTime(Date updateTime) {
            this.updateTime = updateTime == null ? null : (Date) updateTime.clone();
        }
    }

3.4 controller

package com.example.jpa_study.controller;
    
    import com.example.jpa_study.controller.param.StudentParam;
    import com.example.jpa_study.controller.vo.PageData;
    import com.example.jpa_study.repository.entity.Student;
    import com.example.jpa_study.service.StudentService;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.web.bind.annotation.PostMapping;
    import org.springframework.web.bind.annotation.RequestBody;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RestController;
    
    import java.util.List;
    
    @RestController
    @RequestMapping("/student")
    public class StudentController {
        @Autowired
        private StudentService studentService;
    
        @PostMapping("/saveOrUpdate")
        public boolean saveOrUpdate(@RequestBody Student stu) {
            boolean result = false;
            if (stu != null) {
                result = studentService.saveOrUpdate(stu);
            }
            return result;
        }
    
        @PostMapping("/deleteStudentById")
        public boolean deleteStudentById(@RequestBody List<String> ids) {
            boolean result = studentService.deleteStudentById(ids);
            return result;
        }
    
        @PostMapping("/list")
        public PageData<Student> list(@RequestBody StudentParam params){
            PageData<Student> students = studentService.list(params);
            return students;
        }
    
    
    
    }

3.5 service以及impl

package com.example.jpa_study.service;
    
    import com.example.jpa_study.controller.param.StudentParam;
    import com.example.jpa_study.controller.vo.PageData;
    import com.example.jpa_study.repository.entity.Student;
    
    import java.util.List;
    
    
    public interface StudentService {
        /**
         * 添加或修改学生信息
         *
         * @param stu
         * @return
         */
        boolean saveOrUpdate(Student stu);
    
        /**
         * 删除学生信息
         *
         * @param ids
         * @return
         */
        boolean deleteStudentById(List<String> ids);
    
        /**
         * 多条件模糊查询学生信息
         *
         * @param params
         * @return
         */
        PageData<Student> list(StudentParam params);
    
    }

package com.example.jpa_study.service.impl;
    
    import ch.qos.logback.core.util.TimeUtil;
    import com.example.jpa_study.controller.param.StudentParam;
    import com.example.jpa_study.controller.vo.PageData;
    import com.example.jpa_study.repository.StudentRepository;
    import com.example.jpa_study.repository.entity.Student;
    import com.example.jpa_study.service.StudentService;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.data.domain.Page;
    import org.springframework.data.domain.PageRequest;
    import org.springframework.data.domain.Pageable;
    import org.springframework.data.domain.Sort;
    import org.springframework.stereotype.Service;
    
    import javax.persistence.criteria.Predicate;
    import java.util.ArrayList;
    import java.util.Calendar;
    import java.util.Date;
    import java.util.List;
    
    @Service
    public class StudentServiceImpl implements StudentService {
        @Autowired
        private StudentRepository studentRepository;
    
        @Override
        public boolean saveOrUpdate(Student stu) {
            Student student = studentRepository.save(stu);
            return student != null;
        }
    
        @Override
        public boolean deleteStudentById(List<String> ids) {
            if (ids != null && ids.size() > 0) {
                int num = 0;
                for (String id : ids) {
                    studentRepository.deleteById(id);
                    num++;
                }
                return num == ids.size();
            }
            return false;
        }
    
        @Override
        public PageData<Student> list(StudentParam content) {
            int pageNo = 1;
            int pageSize = 20;
            if (content.getPageNo() != null && content.getPageSize() != null) {
                pageNo = content.getPageNo();
                pageSize = content.getPageSize();
            }
            PageData<Student> basePage = new PageData<>();
            List<Sort.Order> orders = new ArrayList<>();
            orders.add(new Sort.Order(Sort.Direction.DESC, "updateTime"));
            Sort sort = Sort.by(orders);
            Pageable pageable = PageRequest.of(pageNo - 1, pageSize, sort);
            Page page = studentRepository.findAll((root, criteriaQuery, criteriaBuilder) -> {
                List<Predicate> predicateList = new ArrayList<>();
                if (content.getName() != null && content.getName() != "") {
                    String title=content.getName();
                    if(title.contains("_") || title.contains("%")){
                        //注："\"被作为转义字符时必须也被转义
                        title = title.replace("\\","\\\\").replace("_","\\_").replace("%","\\%");
                        predicateList.add(criteriaBuilder.and(criteriaBuilder.like(root.get("name"), "%" + title + "%",'\\')));
                    }else{
                        predicateList.add(criteriaBuilder.and(criteriaBuilder.like(root.get("name"), "%" + content.getName() + "%")));
                    }
                }
                if (content.getAddress() != null && content.getAddress() != "") {
                    String title=content.getAddress();
                    if(title.contains("_") || title.contains("%")){
                        //注："\"被作为转义字符时必须也被转义
                        title = title.replace("\\","\\\\").replace("_","\\_").replace("%","\\%");
                        predicateList.add(criteriaBuilder.and(criteriaBuilder.like(root.get("address"), "%" + title + "%",'\\')));
                    }else{
                        predicateList.add(criteriaBuilder.and(criteriaBuilder.like(root.get("address"), "%" + content.getAddress() + "%")));
                    }
                }
                return criteriaBuilder.and(
                        predicateList.toArray(new Predicate[predicateList.size()]));
            }, pageable);
    
            if (null != page && page.getSize() > 0) {
                List<Student> result = page.getContent();
                for (Student stu : result) {
                    Date birthDay = stu.getBirthDay();
                    Integer age=getStudentAge(birthDay);
                    stu.setAge(age);
                }
                basePage.setList(result);
                basePage.setTotal(page.getTotalElements());
            }
            return basePage;
        }
    
        private Integer getStudentAge(Date birthDay) {
            Calendar cal = Calendar.getInstance();
            if (cal.before(birthDay)) {
                //出生日期晚于当前时间，无法计算
                throw new IllegalArgumentException(
                        "The birthDay is before Now.It's unbelievable!");
            }
            //当前年份
            int yearNow = cal.get(Calendar.YEAR);
            int monthNow = cal.get(Calendar.MONTH);
            int dayOfMonthNow = cal.get(Calendar.DAY_OF_MONTH);
            cal.setTime(birthDay);
            int yearBirth = cal.get(Calendar.YEAR);
            int monthBirth = cal.get(Calendar.MONTH);
            int dayOfMonthBirth = cal.get(Calendar.DAY_OF_MONTH);
            //计算整岁数
            int age = yearNow - yearBirth;
            if (monthNow <= monthBirth) {
                if (monthNow == monthBirth) {
                    //当前日期在生日之前，年龄减一
                    if (dayOfMonthNow < dayOfMonthBirth) {
                        age--;
                    }
                } else {
                    //当前月份在生日之前，年龄减一
                    age--;
                }
            } return age;
        }
    }

3.6 Repository

package com.example.jpa_study.repository;
    
    import com.example.jpa_study.repository.entity.Student;
    import org.springframework.data.domain.Page;
    import org.springframework.data.domain.Pageable;
    import org.springframework.data.jpa.domain.Specification;
    import org.springframework.data.jpa.repository.JpaRepository;
    import org.springframework.stereotype.Repository;
    
    @Repository
    public interface StudentRepository extends JpaRepository<Student,String> {
        /**
         * 多条件模糊查询
         *
         * @param spec
         * @param pageable
         * @return
         */
        Page<Student> findAll(Specification<Student> spec, Pageable pageable);
    }

3.7 启动类

package com.example.jpa_study;
    
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    
    @SpringBootApplication
    public class JpaStudyApplication {
    
        public static void main(String[] args) {
            SpringApplication.run(JpaStudyApplication.class, args);
        }
    
    }

3.8 JPA生成的数据库表结构

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1RoZV9CZXN0X0hhY2tlcg_size_16_color_FFFFFF_t_70 1][]

3.9 数据表中的现有数据

![20210223201151110.png][]

3.10 postman测试（添加和查询）

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1RoZV9CZXN0X0hhY2tlcg_size_16_color_FFFFFF_t_70 2][]

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[Link 1]: https://baike.baidu.com/item/%E5%AF%B9%E8%B1%A1%E6%8C%81%E4%B9%85%E5%8C%96/7316192
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[20210223201151110.png]: /images/20210811/6bbd4d2d776e4659b311851f093abf6b.png
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