Spring Data JPA关联查询和@Query

深藏阁楼爱情的钟 2022-05-10 12:12 349阅读 0赞

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][http_localhost_8080_student_getClazzStus_clazzName_Java]开发

![70][]

[http_localhost_8080_student_getClazzStus_clazzName_Java]: http://localhost:8080/student/getClazzStus?clazzName=Java%E5%BC%80%E5%8F%91
[70]: /images/20220510/0a9a8019806745a98fed6b6ba273971f.png