关于JpaRepository的关联查询和@Query查询

目录

• 一 pom
• 二 启动类
• 三 配置文件
• 四 新建数据库
• 五 实体类
• 1 Clazz
• 2 Student
• 六 控制器
• 七 Repository层
• 1 ClazzRepository
• 2 StudentRepository
• 八 Service层
• 九 测试

一 pom

<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>org.fkit</groupId>
     <artifactId>springdatajpaquerytest</artifactId>
     <version>0.0.1-SNAPSHOT</version>
     <packaging>jar</packaging>
     <name>springdatajpaquerytest</name>
     <url>http://maven.apache.org</url>
     <!-- spring-boot-starter-parent是Spring Boot的核心启动器，  包含了自动配置、日志和YAML等大量默认的配置，大大简化了我们的开发。
           引入之后相关的starter引入就不需要添加version配置， spring  boot会自动选择最合适的版本进行添加。 -->
     <parent>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-parent</artifactId>
           <version>2.0.0.RELEASE</version>
           <relativePath />
     </parent>
     <properties>
           <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
           <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
           <java.version>1.8</java.version>
     </properties>
     <dependencies>
           <!-- 添加spring-boot-starter-web模块依赖 -->
           <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
           </dependency>
           <!-- 添加spring-boot-starter-thymeleaf模块依赖 -->
           <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-thymeleaf</artifactId>
           </dependency>
           <!-- 添加MySQL依赖 -->
           <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
           </dependency>
           <!-- 添加Spring Data JPA依赖 -->
           <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-data-jpa</artifactId>
           </dependency>
           <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <scope>test</scope>
           </dependency>
     </dependencies>
</project>

二 启动类

package org.fkit.springdatajpaquerytest;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class App
{
    public static void main( String[] args )
    {
        // SpringApplication 用于从main方法启动Spring应用的类。
        SpringApplication.run(App.class, args);
    }
}

三 配置文件

########################################################
### \u6570\u636E\u6E90\u4FE1\u606F\u914D\u7F6E
########################################################
# \u6570\u636E\u5E93\u5730\u5740
spring.datasource.url=jdbc:mysql://localhost:3306/springdatajpaquery
# \u7528\u6237\u540D
spring.datasource.username=root
# \u5BC6\u7801
spring.datasource.password=
# \u6570\u636E\u5E93\u9A71\u52A8
spring.datasource.driverClassName=com.mysql.jdbc.Driver
#  \u6307\u5B9A\u8FDE\u63A5\u6C60\u4E2D\u6700\u5927\u7684\u6D3B\u8DC3\u8FDE\u63A5\u6570.
spring.datasource.max-active=20
#  \u6307\u5B9A\u8FDE\u63A5\u6C60\u6700\u5927\u7684\u7A7A\u95F2\u8FDE\u63A5\u6570\u91CF.
spring.datasource.max-idle=8
#  \u6307\u5B9A\u5FC5\u987B\u4FDD\u6301\u8FDE\u63A5\u7684\u6700\u5C0F\u503C
spring.datasource.min-idle=8
#  \u6307\u5B9A\u542F\u52A8\u8FDE\u63A5\u6C60\u65F6\uFF0C\u521D\u59CB\u5EFA\u7ACB\u7684\u8FDE\u63A5\u6570\u91CF
spring.datasource.initial-size=10
########################################################
### JPA\u6301\u4E45\u5316\u914D\u7F6E
########################################################
# \u6307\u5B9A\u6570\u636E\u5E93\u7684\u7C7B\u578B
spring.jpa.database=MySQL
#  \u6307\u5B9A\u662F\u5426\u9700\u8981\u5728\u65E5\u5FD7\u4E2D\u663E\u793Asql\u8BED\u53E5
spring.jpa.show-sql=true
#  \u6307\u5B9A\u81EA\u52A8\u521B\u5EFA|\u66F4\u65B0|\u9A8C\u8BC1\u6570\u636E\u5E93\u8868\u7ED3\u6784\u7B49\u914D\u7F6E\uFF0C\u914D\u7F6E\u6210update
#  \u8868\u793A\u5982\u679C\u6570\u636E\u5E93\u4E2D\u5B58\u5728\u6301\u4E45\u5316\u7C7B\u5BF9\u5E94\u7684\u8868\u5C31\u4E0D\u521B\u5EFA\uFF0C\u4E0D\u5B58\u5728\u5C31\u521B\u5EFA\u5BF9\u5E94\u7684\u8868
spring.jpa.hibernate.ddl-auto=update
# Naming strategy
# \u6307\u5B9A\u547D\u540D\u7B56\u7565
spring.jpa.hibernate.naming-strategy=org.hibernate.cfg.ImprovedNamingStrategy
# \u6307\u5B9A\u6570\u636E\u5E93\u65B9\u8A00
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5Dialect

四 新建数据库

springdatajpaquery

五 实体类

1 Clazz

package org.fkit.springdatajpaquerytest.bean;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="tb_clazz")
public class Clazz implements Serializable{

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int code ;
    private String name ;
    // 班级与学生是一对多的关联
    @OneToMany(
               fetch=FetchType.LAZY,
               targetEntity=Student.class,
               mappedBy="clazz"
            )
    private Set<Student> students = new HashSet<>();

    public Clazz() {

    }
    // 班级对象
    public Clazz(String name) {
        this.name = name;
    }
    public int getCode() {
        return code;
    }
    public void setCode(int code) {
        this.code = code;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Set<Student> getStudents() {
        return students;
    }
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
}

2 Student

package org.fkit.springdatajpaquerytest.bean;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="tb_student")
public class Student implements Serializable{
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    private String name ;
    private String address ;
    private int age ;
    private char sex;
    // 学生与班级是多对一的关系，这里配置的是双向关联
    @ManyToOne(fetch=FetchType.LAZY,
            targetEntity=Clazz.class
            )
    @JoinColumn(name="clazzId",referencedColumnName="code")
    private Clazz clazz ;
    public Student() {

    }
    public Student(String name, String address, int age, char sex,
            Clazz clazz) {
        super();
        this.name = name;
        this.address = address;
        this.age = age;
        this.sex = sex;
        this.clazz = clazz;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    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 int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public char getSex() {
        return sex;
    }
    public void setSex(char sex) {
        this.sex = sex;
    }
    public Clazz getClazz() {
        return clazz;
    }
    public void setClazz(Clazz clazz) {
        this.clazz = clazz;
    }
}

六 控制器

package org.fkit.springdatajpaquerytest.controller;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import javax.annotation.Resource;
import org.fkit.springdatajpaquerytest.bean.Clazz;
import org.fkit.springdatajpaquerytest.bean.Student;
import org.fkit.springdatajpaquerytest.service.SchoolService;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

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

    // 注入ShcoolService
    @Resource
    private SchoolService schoolService;
    @RequestMapping("/save")
    public String save() {

        Clazz clazz1 = new Clazz("疯狂java开发1班");
        Clazz clazz2 = new Clazz("疯狂java开发2班");
        // 保存班级对象数据
        List<Clazz> clazzs = new ArrayList<>();
        clazzs.add(clazz1);
        clazzs.add(clazz2);
        schoolService.saveClazzAll(clazzs);

        Student swk = new Student("孙悟空","广州",700,'男',clazz1);
        Student zzj = new Student("蜘蛛精","广州",700,'女',clazz1);
        Student nmw = new Student("牛魔王","广州",500,'男',clazz2);

        List<Student> students = new ArrayList<>();
        students.add(swk);
        students.add(zzj);
        students.add(nmw);
        schoolService.saveStudentAll(students);
        return "保存学生对象成功";
    }
    /**
     * 查询某个班级下所有的学生姓名，年龄，性别
     * @param clazzName
     * @return
     */
    @RequestMapping("/getClazzStus")
    public List<Map<String, Object>> getClazzStus(String clazzName){
        return schoolService.getStusByClazzName(clazzName);
    }
    /**
     * 查询某个班级下所有的学生姓名，性别
     * @param clazzName
     * @return
     */
    @RequestMapping("/findNameAndSexByClazzName")
    public List<Map<String, Object>> findNameAndSexByClazzName(String clazzName){
        return schoolService.findNameAndSexByClazzName(clazzName);
    }
    /**
     * ，查询某个班级下某种性别的所有学生的姓名
     * @param clazzName
     * @return
     */
    @RequestMapping("/findNameByClazzNameAndSex")
    public List<String> findNameByClazzNameAndSex(String clazzName ,Character sex){
        return schoolService.findNameByClazzNameAndSex(clazzName ,sex);
    }
    /**
     * 查询某个学生属于哪个班级
     * @param clazzName
     * @return
     */
    @RequestMapping("/findClazzNameByStuName")
    public String findClazzNameByStuName(String stuName){
        return schoolService.findClazzNameByStuName(stuName);
    }
    /**
     * 删除某个学生对象
     * @param clazzName
     * @return
     */
    @RequestMapping("/deleteStuByStuName")
    public String deleteStuByStuName(String stuName){
        return "删除数据："+schoolService.deleteStuByStuName(stuName);
    }
}

七 Repository层

1 ClazzRepository

package org.fkit.springdatajpaquerytest.repository;
import org.fkit.springdatajpaquerytest.bean.Clazz;
import org.springframework.data.jpa.repository.JpaRepository;
public interface ClazzRepository extends JpaRepository<Clazz, Integer> {
}

2 StudentRepository

package org.fkit.springdatajpaquerytest.repository;
import java.util.List;
import java.util.Map;
import org.fkit.springdatajpaquerytest.bean.Student;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
public interface StudentRepository extends JpaRepository<Student, Integer> {

    /**
     * 根据班级名称查询这个班级下所有的学生信息
     * 相当于JPQL语句： select s from Student s where s.clazz.name = ?1
     * @param clazzName
     * @return
     */
    List<Student> findByClazz_name(String clazzName);

    /**
     * @Query写法
     * 根据班级名称查询这个班级下所有的学生信息
     * ?1此处使用的是参数的位置，代表的是第一个参数
     * 此写法与 findByClazz_name方法实现的功能完全一致
     * */
    @Query("select s from Student s where s.clazz.name = ?1")
    List<Student> findStudentsByClazzName(String clazzName);
    /**
     * 使用@Query注解的形式，查询某个班级下所有学生的姓名和性别
     * @param clazzName
     * @return
     */
    @Query("select new Map(s.name as name , s.sex as sex) "
            + "from Student s where s.clazz.name = ?1")
    List<Map<String, Object>> findNameAndSexByClazzName(String clazzName);

    /**
     *  使用@Query注解的形式，查询某个班级下某种性别的所有学生的姓名
     *  上面方法是用的是参数的位置来查询的，Spring Data JPA中还支持用
     *  名称来匹配查询使用格式 “:参数名称” 引用
     * @param clazzName
     * @return
     */
    @Query("select s.name from Student s "
            + "where s.clazz.name = :clazzName and s.sex = :sex ")
    List<String> findNameByClazzNameAndSex(@Param("clazzName")String clazzName , @Param("sex")char sex);
    /**
     *  使用@Query注解的形式，查询某个学生属于哪个班级
     * @param stuName
     * @return
     */
    @Query("select c.name from Clazz c inner join c.students s "
            + "where s.name = ?1 ")
    String findClazzNameByStuName(String stuName);
    /**
     * 执行更新查询，使用@Query与@Modifying可以执行更新操作
     * 例如删除牛魔王这个学生
     * */
    @Modifying
    @Query("delete from Student s where s.name = ?1")
    int deleteStuByStuName(String stuName);
}

八 Service层

package org.fkit.springdatajpaquerytest.service;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.annotation.Resource;
import org.fkit.springdatajpaquerytest.bean.Clazz;
import org.fkit.springdatajpaquerytest.bean.Student;
import org.fkit.springdatajpaquerytest.repository.ClazzRepository;
import org.fkit.springdatajpaquerytest.repository.StudentRepository;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
@Service
public class SchoolService {

    // 注入数据访问层接口对象
    @Resource
    private StudentRepository studentRepository;
    @Resource
    private ClazzRepository clazzRepository;

    @Transactional
    public void saveClazzAll(List<Clazz> clazzs) {
        clazzRepository.saveAll(clazzs);
    }
    @Transactional
    public void saveStudentAll(List<Student> students) {
        studentRepository.saveAll(students);
    }

    public List<Map<String, Object>> getStusByClazzName(String clazzName) {
        // 使用"_" 和 @Query查询方式结果一致
        List<Student> students = studentRepository.findByClazz_name(clazzName);
//        List<Student> students = studentRepository.findStudentsByClazzName(clazzName);
        List<Map<String, Object>>  results = new ArrayList<>();
        // 遍历查询出的学生对象，提取姓名，年龄，性别信息
        for(Student student:students){
            Map<String , Object> stu = new HashMap<>();
            stu.put("name", student.getName());
            stu.put("age", student.getAge());
            stu.put("sex", student.getSex());
            results.add(stu);
        }
        return results;
    }
    public List<Map<String, Object>> findNameAndSexByClazzName(String clazzName) {
        return studentRepository.findNameAndSexByClazzName(clazzName);
    }
    public List<String> findNameByClazzNameAndSex(
            String clazzName, char sex) {
        return studentRepository.findNameByClazzNameAndSex(clazzName, sex);
    }
    public String findClazzNameByStuName(String stuName) {
        return studentRepository.findClazzNameByStuName(stuName);
    }
    @Transactional
    public int deleteStuByStuName(String stuName) {
        return studentRepository.deleteStuByStuName(stuName);
    }
}

九 测试

以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。