如何理解JpaRepository的关联查询和@Query查询

如何理解JpaRepository的关联查询和@Query查询，针对这个问题，这篇文章详细介绍了相对应的分析和解答，希望可以帮助更多想解决这个问题的小伙伴找到更简单易行的方法。

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;  @SpringBootApplicationpublic 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\u5740spring.datasource.url=jdbc:mysql://localhost:3306/springdatajpaquery# \u7528\u6237\u540Dspring.datasource.username=root# \u5BC6\u7801spring.datasource.passWord=# \u6570\u636E\u5E93\u9A71\u52A8spring.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\u503Cspring.datasource.min-idle=8#  \u6307\u5B9A\u542F\u52A8\u8FDE\u63A5\u6C60\u65F6\uFF0C\u521D\u59CB\u5EFA\u7ACB\u7684\u8FDE\u63A5\u6570\u91CFspring.datasource.initial-size=10########################################################### JPA\u6301\u4E45\u5316\u914D\u7F6E######################################################### \u6307\u5B9A\u6570\u636E\u5E93\u7684\u7C7B\u578Bspring.jpa.database=MySQL#  \u6307\u5B9A\u662F\u5426\u9700\u8981\u5728\u65E5\u5FD7\u4E2D\u663E\u793Asql\u8BED\u53E5spring.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\u8868spring.jpa.hibernate.ddl-auto=update# Naming strategy# \u6307\u5B9A\u547D\u540D\u7B56\u7565spring.jpa.hibernate.naming-strategy=org.hibernate.cfg.ImprovedNamingStrategy# \u6307\u5B9A\u6570\u636E\u5E93\u65B9\u8A00spring.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";    }        @RequestMapping("/getClazzStus")    public List<Map<String, Object>> getClazzStus(String clazzName){        return schoolService.getStusByClazzName(clazzName);    }        @RequestMapping("/findNameAndSexByClazzName")    public List<Map<String, Object>> findNameAndSexByClazzName(String clazzName){        return schoolService.findNameAndSexByClazzName(clazzName);    }        @RequestMapping("/findNameByClazzNameAndSex")    public List<String> findNameByClazzNameAndSex(String clazzName ,Character sex){        return schoolService.findNameByClazzNameAndSex(clazzName ,sex);    }        @RequestMapping("/findClazzNameByStuName")    public String findClazzNameByStuName(String stuName){        return schoolService.findClazzNameByStuName(stuName);    }        @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> {            List<Student> findByClazz_name(String clazzName);            @Query("select s from Student s where s.clazz.name = ?1")    List<Student> findStudentsByClazzName(String clazzName);        @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);            @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);        @Query("select c.name from Clazz c inner join c.students s "            + "where s.name = ?1 ")    String findClazzNameByStuName(String stuName);        @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;@Servicepublic 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

关于如何理解JpaRepository的关联查询和@Query查询问题的解答就分享到这里了，希望以上内容可以对大家有一定的帮助，如果你还有很多疑惑没有解开，可以关注编程网精选频道了解更多相关知识。