Spring Data JPA关联查询和@Query
示例:关联查询和@Query
创建持久化类
程序清单:/jpa/src/main/java/com/dwx/bean/Student.java
package com.dwx.bean;
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="t_student")
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
private String name;
private String sex;
private Integer age;
private String address;
@ManyToOne(fetch=FetchType.LAZY,targetEntity=Clazz.class)
@JoinColumn(name="clazzId",referencedColumnName="code")
private Clazz clazz;
public Student() {
}
public Student(Integer id, String name, String sex, Integer age, String address,Clazz clazz) {
super();
this.id = id;
this.name = name;
this.sex = sex;
this.age = age;
this.address = address;
this.clazz=clazz;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public Clazz getClazz() {
return clazz;
}
public void setClazz(Clazz clazz) {
this.clazz = clazz;
}
}
程序清单:/jpa/src/main/java/com/dwx/bean/Clazz.java
package com.dwx.bean;
import java.util.ArrayList;
import java.util.List;
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="t_class")
public class Clazz {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer code;
private String name;
@OneToMany(
fetch=FetchType.LAZY,targetEntity=Student.class,mappedBy="clazz")
private List<Student> students=new ArrayList<>();
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
public Integer getCode() {
return code;
}
public void setCode(Integer code) {
this.code = code;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
定义数据访问层接口
程序清单:/jpa/src/main/java/com/dwx/repository/StudentRepository.java
package com.dwx.repository;
import java.util.List;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import com.dwx.bean.Student;
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);
}
程序清单:/jpa/src/main/java/com/dwx/repository/ClazzRepository.java
package com.dwx.repository;
import org.springframework.data.jpa.repository.JpaRepository;
import com.dwx.bean.Clazz;
public interface ClazzRepository extends JpaRepository<Clazz, Integer> {
}
定义业务层类
程序清单:/jpa/src/main/java/com/dwx/service/SchoolService.java
package com.dwx.service;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.annotation.Resource;
import org.springframework.stereotype.Service;
import com.dwx.bean.Student;
import com.dwx.repository.ClazzRepository;
import com.dwx.repository.StudentRepository;
@Service
public class SchoolService {
@Resource
private StudentRepository studentRepository;
@Resource
private ClazzRepository clazzRepository;
public List<Map<String,Object>> getStusByClazzName(String clazzName){
//使用"_"和@Query查询结果一致
List<Student> students=studentRepository.findByClazz_name(clazzName);
//List<Student> students=studentRepository.findStudentsByClazzname(clazzName);
List<Map<String,Object>> results=new ArrayList<Map<String,Object>>();
for(Student stu:students) {
Map<String,Object> map=new HashMap<>();
map.put("name", stu.getName());
map.put("sex", stu.getSex());
map.put("age", stu.getAge());
map.put("address", stu.getAddress());
results.add(map);
}
return results;
}
}
定义控制器类
程序清单:/jpa/src/main/java/com/dwx/controller/StudentController.java
package com.dwx.controller;
import java.util.List;
import java.util.Map;
import javax.annotation.Resource;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import com.dwx.service.SchoolService;
@RestController
@RequestMapping("/student")
public class StudentController {
@Resource
private SchoolService schoolService;
@RequestMapping("/getClazzStus")
public List<Map<String,Object>> getClazzStus(String clazzName){
return schoolService.getStusByClazzName(clazzName);
}
}
测试应用
启动Spring Boot项目,在浏览器中输入以下地址:http://localhost:8080/student/getClazzStus?clazzName=Java开发