SpringBoot简单使用JPA

springboot , , 评论

基础pom.xml

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<?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>cn.idea360</groupId>
    <artifactId>jpa-demo</artifactId>
    <version>0.0.1</version>
    <name>jpa-demo</name>
    <description>jpa-demo</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>2.6.13</spring-boot.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>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </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>${spring-boot.version}</version>
                <configuration>
                    <mainClass>cn.idea360.jpa.JpaDemoApplication</mainClass>
                    <skip>true</skip>
                </configuration>
                <executions>
                    <execution>
                        <id>repackage</id>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

配置文件application.properties

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# 应用服务 WEB 访问端口
server.port=8080
#************H2  Begin****************
##创建表的MySql语句位置
#spring.datasource.schema=classpath:schema.sql
##插入数据的MySql语句的位置
#spring.datasource.data=classpath:data.sql
#remote visit
spring.h2.console.settings.web-allow-others=true
#console url。Spring启动后，可以访问 http://127.0.0.1:8080/h2-console 查看数据库
spring.h2.console.path=/h2-console
#default true。咱也可以用命令行访问好数据库，感兴趣的同学点这个链接 http://www.h2database.com/html/tutorial.html?highlight=Mac&search=mac#firstFound
spring.h2.console.enabled=true
spring.h2.console.settings.trace=true
#指定数据库的种类，这里 file意思是文件型数据库
spring.datasource.url=jdbc:h2:file:./data/jpa-h2
#用户名密码不需要改，都是临时值
spring.datasource.username=san
spring.datasource.password=
#指定Driver，有了Driver才能访问数据库
spring.datasource.driver-class-name=org.h2.Driver

spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=update

使用 @ManyToOne进行单向关联

场景：一个部门里有多个员工。

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package cn.idea360.jpa.entity;

import lombok.Data;

import javax.persistence.*;
import java.io.Serializable;

/**
 * @author cuishiying
 */
@Data
@Entity
@Table(name = "hr_employee")
public class Employee implements Serializable {

    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer employeeId;

    @Column(name = "employee_name")
    private String employeeName;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name="departmentId")
    private Department department;

}
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package cn.idea360.jpa.entity;

import lombok.Data;

import javax.persistence.*;
import java.io.Serializable;

/**
 * @author cuishiying
 */
@Data
@Entity
@Table(name = "hr_department")
public class Department implements Serializable {

    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer departmentId;

    @Column(name = "department_name")
    private String departmentName;

}

在这样的设定下, 是由Employee维护对Department的参考来维持多对一的关系，Department并没有意识到Employee的存在，而在存储时，由于设定了CascadeType.ALL，所以直接存储Employee实例时，所参考的Department也会一并被存储。

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package cn.idea360.jpa.repository;

import cn.idea360.jpa.entity.Department;
import cn.idea360.jpa.entity.Employee;
import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

import javax.annotation.Resource;
import javax.transaction.Transactional;
import java.util.Arrays;

@Slf4j
@SpringBootTest
class EmployeeRepositoryTest {

    @Resource
    private DepartmentRepository departmentRepository;
    @Resource
    private EmployeeRepository employeeRepository;
    @Resource
    private ObjectMapper objectMapper;

    /**
     * 必须开启事务
     */
    @Test
    @Transactional
    void addAndGetEmployee() throws Exception {
        Department department = new Department();
        department.setDepartmentName("技术部");

        Employee employee1 = new Employee();
        employee1.setEmployeeName("张三");
        employee1.setDepartment(department);

        Employee employee2 = new Employee();
        employee2.setEmployeeName("李四");
        employee2.setDepartment(department);

        employeeRepository.saveAll(Arrays.asList(employee1, employee2));

        Department department1 = departmentRepository.findById(1).get();
        log.info("db department: {}", objectMapper.writeValueAsString(department1));

        Employee employee = employeeRepository.getById(2);
        log.info("db employee: {}", objectMapper.writeValueAsString(employee));
    }
}

日志输出:

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Hibernate: insert into hr_department (id, department_name) values (default, ?)
Hibernate: insert into hr_employee (id, department_id, employee_name) values (default, ?, ?)
Hibernate: insert into hr_employee (id, department_id, employee_name) values (default, ?, ?)
2023-06-11 13:36:19.592  INFO 35924 --- [           main] c.i.j.repository.EmployeeRepositoryTest  : db department: {"departmentId":1,"departmentName":"技术部"}
2023-06-11 13:36:19.595  INFO 35924 --- [           main] c.i.j.repository.EmployeeRepositoryTest  : db employee: {"employeeId":2,"employeeName":"李四","department":{"departmentId":1,"departmentName":"技术部"}}

使用 @OneToMany进行单向关联

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package cn.idea360.jpa.entity;

import lombok.Data;

import javax.persistence.*;
import java.io.Serializable;
import java.util.List;

/**
 * @author cuishiying
 */
@Data
@Entity
@Table(name = "hr_department")
public class Department implements Serializable {

    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer departmentId;

    @Column(name = "department_name")
    private String departmentName;

    @OneToMany(cascade = CascadeType.ALL)
    // 不加JoinColumn会生成中间表
    @JoinColumn(name = "department_id")
    private List<Employee> employees;
}
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package cn.idea360.jpa.entity;

import lombok.Data;

import javax.persistence.*;
import java.io.Serializable;

/**
 * @author cuishiying
 */
@Data
@Entity
@Table(name = "hr_employee")
public class Employee implements Serializable {

    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer employeeId;

    @Column(name = "employee_name")
    private String employeeName;

}
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package cn.idea360.jpa.repository;

import cn.idea360.jpa.entity.Department;
import cn.idea360.jpa.entity.Employee;
import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.annotation.Rollback;

import javax.annotation.Resource;
import javax.transaction.Transactional;
import java.util.Arrays;

@Slf4j
@SpringBootTest
class EmployeeRepositoryTest {

    @Resource
    private DepartmentRepository departmentRepository;
    @Resource
    private EmployeeRepository employeeRepository;
    @Resource
    private ObjectMapper objectMapper;

    /**
     * 必须开启事务
     */
    @Test
    @Transactional
    @Rollback(value = false)
    void addAndGetDepartment() throws Exception {
        Employee employee1 = new Employee();
        employee1.setEmployeeName("张三");

        Employee employee2 = new Employee();
        employee2.setEmployeeName("李四");

        Department department = new Department();
        department.setDepartmentName("技术部");
        department.setEmployees(Arrays.asList(employee1, employee2));

        departmentRepository.save(department);

        Department department1 = departmentRepository.findById(1).get();
        log.info("db department: {}", objectMapper.writeValueAsString(department1));
        // FetchType.LAZY使用
        log.info("db department.employees: {}", objectMapper.writeValueAsString(department1.getEmployees()));

        Employee employee = employeeRepository.getById(2);
        log.info("db employee: {}", objectMapper.writeValueAsString(employee));
    }
}

输出

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Hibernate: insert into hr_department (id, department_name) values (default, ?)
Hibernate: insert into hr_employee (id, employee_name) values (default, ?)
Hibernate: insert into hr_employee (id, employee_name) values (default, ?)
Hibernate: select department0_.id as id1_0_0_, department0_.department_name as departme2_0_0_ from hr_department department0_ where department0_.id=?
Hibernate: select employees0_.department_id as departme3_1_0_, employees0_.id as id1_1_0_, employees0_.id as id1_1_1_, employees0_.employee_name as employee2_1_1_ from hr_employee employees0_ where employees0_.department_id=?
2023-06-11 14:53:40.497  INFO 37827 --- [           main] c.i.j.repository.EmployeeRepositoryTest  : db department: {"departmentId":1,"departmentName":"技术部","employees":[{"employeeId":1,"employeeName":"张三"},{"employeeId":2,"employeeName":"李四"}]}
2023-06-11 14:53:40.498  INFO 37827 --- [           main] c.i.j.repository.EmployeeRepositoryTest  : db department.employees: [{"employeeId":1,"employeeName":"张三"},{"employeeId":2,"employeeName":"李四"}]
2023-06-11 14:53:40.500  INFO 37827 --- [           main] c.i.j.repository.EmployeeRepositoryTest  : db employee: {"employeeId":2,"employeeName":"李四"}
Hibernate: update hr_employee set department_id=? where id=?
Hibernate: update hr_employee set department_id=? where id=?

@OneToMany和@ManyToOne同时使用：双向的关联

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package cn.idea360.jpa.entity;

import lombok.Data;

import javax.persistence.*;
import java.io.Serializable;

/**
 * @author cuishiying
 */
@Data
@Entity
@Table(name = "hr_employee")
public class Employee implements Serializable {

    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer employeeId;

    @Column(name = "employee_name")
    private String employeeName;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name="departmentId")
    private Department department;

}
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package cn.idea360.jpa.entity;

import lombok.Data;

import javax.persistence.*;
import java.io.Serializable;
import java.util.List;

/**
 * @author cuishiying
 */
@Data
@Entity
@Table(name = "hr_department")
public class Department implements Serializable {

    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer departmentId;

    @Column(name = "department_name")
    private String departmentName;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Employee> employees;
}

测试还有问题

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package cn.idea360.jpa.repository;

import cn.idea360.jpa.entity.Department;
import cn.idea360.jpa.entity.Employee;
import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

import javax.annotation.Resource;
import javax.transaction.Transactional;
import java.util.Arrays;

@Slf4j
@SpringBootTest
class EmployeeRepositoryTest {

    @Resource
    private DepartmentRepository departmentRepository;
    @Resource
    private EmployeeRepository employeeRepository;
    @Resource
    private ObjectMapper objectMapper;

    /**
     * 必须开启事务
     */
    @Test
    @Transactional
    void addAndGetDepartment() throws Exception {
        Employee employee1 = new Employee();
        employee1.setEmployeeName("张三");

        Employee employee2 = new Employee();
        employee2.setEmployeeName("李四");

        Department department = new Department();
        department.setDepartmentName("技术部");
        department.setEmployees(Arrays.asList(employee1, employee2));

        departmentRepository.save(department);

        Department department1 = departmentRepository.findById(1).get();
        log.info("db department: {}", objectMapper.writeValueAsString(department1));
        // FetchType.LAZY使用
        log.info("db department.employees: {}", objectMapper.writeValueAsString(department1.getEmployees()));

        Employee employee = employeeRepository.getById(2);
        log.info("db employee: {}", objectMapper.writeValueAsString(employee));
    }

    @Test
    @Transactional
    void addAndGetEmployee() throws Exception {
        Department department = new Department();
        department.setDepartmentName("技术部");

        Employee employee1 = new Employee();
        employee1.setEmployeeName("张三");
        employee1.setDepartment(department);

        Employee employee2 = new Employee();
        employee2.setEmployeeName("李四");
        employee2.setDepartment(department);

        employeeRepository.saveAll(Arrays.asList(employee1, employee2));

        Department department1 = departmentRepository.findById(1).get();
        log.info("db department: {}", objectMapper.writeValueAsString(department1));
        // FetchType.LAZY使用
        log.info("db department.employees: {}", objectMapper.writeValueAsString(department1.getEmployees()));

        Employee employee = employeeRepository.getById(2);
        log.info("db employee: {}", objectMapper.writeValueAsString(employee));
    }
}

参考

当我遇上你

勿在浮沙筑高楼