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。
<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>
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);
}
}######################################################## ### \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
springdatajpaquery
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;
}
}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;
}
}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);
}
}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> {
}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);
}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);
}
}
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，可以关注亿速云行业资讯频道了解更多相关知识。
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