SpringBoot整合Spring Data JPA(一)

发布于：2020年9月10日

一、OverView

JPA(Java Persistence API)是Sun官方提出的Java持久化规范。它为Java开发人员提供了一种对象/关联映射工具来管理Java应用中的关系数据。

Spring Data JPA 是 Spring 基于 ORM 框架、JPA 规范的基础上封装的一套JPA应用框架，可使开发者用极简的代码即可实现对数据的访问和操作。它提供了包括增删改查等在内的常用功能，且易于扩展！学习并使用 Spring Data JPA 可以极大提高开发效率！

spring data jpa让我们解脱了DAO层的操作，基本上所有CRUD都可以依赖于它来实现

二、环境搭建

pom.xml

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

application.properties

spring.datasource.url=jdbc:mysql://localhost:3306/jpa
spring.datasource.username=root
spring.datasource.password=
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

spring.jpa.database=mysql
# 是否在控制台打印 sql 语句
spring.jpa.show-sql=true
# 使用 InnoDB 作为引擎 
spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect
# 每次启动都会更新数据库，如：增加字段等，但是对某个字段进行改造是识别不出来
spring.jpa.hibernate.ddl-auto=update

entiy

Student

@Entity
@Table(name = "student")
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", columnDefinition = "INT UNSIGNED COMMENT '自增主键'")
    private Long id;

    @Column(name = "name", columnDefinition = "VARCHAR(50) NOT NULL COMMENT '用户名'")
    private String name;

    @Column(name = "pwd", columnDefinition = "VARCHAR(100) DEFAULT NULL COMMENT '密码'")
    private String pwd;
  
    // 省略 set get

}

Grade

@Entity
@Table(name = "grade")
public class Grade {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", columnDefinition = "INT UNSIGNED COMMENT '自增主键'")
    private Long id;

    @Column(name = "subject", columnDefinition = "VARCHAR(50) NOT NULL COMMENT '学科'")
    private String subject;

    @Column(name = "score", columnDefinition = "TINYINT UNSIGNED NOT NULL COMMENT '成绩'")
    private String score;

    // 省略 set get
}

注：这次使用两个表，为了后面进行复杂查询准备，这里的将两个表的自增 id 关联在一起，就不考虑多对多了

repository

StudentRepository

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@Repository
public interface StudentRepository extends JpaRepository<Student, Long>, JpaSpecificationExecutor<Student> {
}

GradeRepository

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@Repository
public interface GradeRepository extends JpaRepository<Grade, Long>, JpaSpecificationExecutor<Grade> {
}

在上次 aop 那里面就提过，由于继承的有 CRUD 的 repository 和一些其他的，这也是上面提到的解放 DAO 层的操作，具体的可以看下图

三、CRUD

controller

GradeController

@RestController
@RequestMapping("/grade")
public class GradeController {

    private GradeRepository gradeRepository;

    @Autowired
    public void setGradeRepository(GradeRepository gradeRepository) {
        this.gradeRepository = gradeRepository;
    }

    @PutMapping("/add")
    public Grade add(@RequestBody Grade grade) {
        return gradeRepository.save(grade);
    }

    @GetMapping("/query")
    public List<Grade> query() {
        return gradeRepository.findAll();
    }

    @PostMapping("/update")
    public Grade update(@RequestBody Grade grade) {
        return gradeRepository.save(grade);
    }

    @DeleteMapping("/delete")
    public void delete(@RequestParam Long id) {
        gradeRepository.deleteById(id);
    }
}

StudentController

@RestController
@RequestMapping("/student")
public class StudentController {

    private StudentRepository studentRepository;

    @Autowired
    public void setStudentRepository(StudentRepository studentRepository) {
        this.studentRepository = studentRepository;
    }

    @PutMapping("/add")
    public Student add(@RequestBody Student student) {
        return studentRepository.save(student);
    }

    @GetMapping("/query")
    public List<Student> query() {
        return studentRepository.findAll();
    }

    @PostMapping("/update")
    public Student update(@RequestBody Student student) {
        return studentRepository.save(student);
    }

    @DeleteMapping("/delete")
    public void delete(@RequestParam Long id) {
        studentRepository.deleteById(id);
    }

}