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 students=new ArrayList<>();	
	public List getStudents() {
		return students;
	}
	public void setStudents(List 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 {
	List findByClazz_name(String clazzName);
	
	@Query("select s from Student s where s.clazz.name=?1")
	List 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 {

}

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> getStusByClazzName(String clazzName){
		//使用"_"和@Query查询结果一致
		List students=studentRepository.findByClazz_name(clazzName);
		//List students=studentRepository.findStudentsByClazzname(clazzName);
		List> results=new ArrayList>();
		for(Student stu:students) {
			Map 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> 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