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mybatis学习笔记三(关联关系)
学习mybatis的关联关系,主要注解在代码上,这里不做解释。配置文件一样的就不贴了
1.关联关系表创建(学生对应老师 多对一)
学生老师表
2.表对应的实体类
package com.home.entity; /** * 此类是:学生 * @author hpc * @2017年1月14日下午7:06:33 */ public class Student { private Integer student_id;//学生id private String student_name;//学生名字 private Integer student_number;//学生编号 private Teacher student_teacher;//是哪个教师的学生 public Integer getStudent_id() { return student_id; } public void setStudent_id(Integer student_id) { this.student_id = student_id; } public String getStudent_name() { return student_name; } public void setStudent_name(String student_name) { this.student_name = student_name; } public Integer getStudent_number() { return student_number; } public void setStudent_number(Integer student_number) { this.student_number = student_number; } public Teacher getStudent_teacher() { return student_teacher; } public void setStudent_teacher(Teacher student_teacher) { this.student_teacher = student_teacher; } @Override public String toString() { return "Student [student_id=" + student_id + ", student_name=" + student_name + ", student_number=" + student_number + ", student_teacher=" + student_teacher + "]"; } }
package com.home.entity; import java.util.HashSet; import java.util.Set; /** * 此类是:老师 * @author hpc * @2017年1月14日下午7:06:47 */ public class Teacher { private Integer teacher_id;// 老师id private String teacher_name;// 老师名字 private Integer teacher_number;// 老师编号 private Set<Student> teacher_student = new HashSet<Student>();// 老师教过哪些学生 public Integer getTeacher_id() { return teacher_id; } public void setTeacher_id(Integer teacher_id) { this.teacher_id = teacher_id; } public String getTeacher_name() { return teacher_name; } public void setTeacher_name(String teacher_name) { this.teacher_name = teacher_name; } public Integer getTeacher_number() { return teacher_number; } public void setTeacher_number(Integer teacher_number) { this.teacher_number = teacher_number; } public Set<Student> getTeacher_student() { return teacher_student; } public void setTeacher_student(Set<Student> teacher_student) { this.teacher_student = teacher_student; } @Override public String toString() { return "Teacher [teacher_id=" + teacher_id + ", teacher_name=" + teacher_name + ", teacher_number=" + teacher_number + ", teacher_student=" + teacher_student + "]"; } }
3.核心主要是配置文件
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.home.entity.studentMapper"><!-- 命名空间,一定要是唯一的,只有这样才能定位到这个文件来 --> <!-- 多对一查询(多个学生对应一个老师) --> <!-- select的属性 id:这个查找标签的唯一标识,通过id找到这条sql语句 parameterType:传进来的参数类型 resultMap:这条语句执行完,以什么形式返回结果集 --> <select id="loadStudent" parameterType="int" resultMap="studentMap"> select * from students as s join teachers as t on t.teacher_id=s.student_teacher where s.student_id=#{id} </select> <!-- 学生对象映射关系 --> <!--resultMap的属性 type:以这个类型进行封装返回 id:找到该resultMap标签的唯一标识 resultMap的内部的标签介绍 <id>专门用于映射主键的 <result>普通属性映射 <collection>集合属性映射 <association>关系映射(1-1,1-n,n-1,n-n) <constructor>专门用于映射构造函数的标签 <discriminator>鉴别器非常容易理 解,因为它的表现很像 Java 语言中的 switch 语句。 --> <resultMap type="student" id="studentMap" > <!-- 主键映射 --> <id property="student_id" column="student_id" javaType="int"/> <!-- 普通属性映射 --> <!-- property:映射在这个属性上 column:以这个列上的为参照 javaType:以什么类型映射 --> <result property="student_name" column="student_name" javaType="String"/> <result property="student_number" column="student_number" javaType="int"/> <!-- 关联关系映射 --> <association property="student_teacher" column="teacher_id" resultMap="teacherMap"/> </resultMap> <!-- 学生对象映射关系 --> <resultMap type="teacher" id="teacherMap"> <id property="teacher_id" column="teacher_id" javaType="int"/> <result property="teacher_name" column="teacher_name" javaType="String"/> <result property="teacher_number" column="teacher_number" javaType="int"/> </resultMap> </mapper>
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.home.entity.teacherMapper"> <!-- teacher sql --> <select id="loadTeacher" parameterType="int" resultMap="teacherMapper"> select * from teachers as t join students as s on s.student_teacher=t.teacher_id where teacher_id=#{teacher_id} </select> <resultMap type="teacher" id="teacherMapper"> <id property="teacher_id" column="teacher_id" /> <result property="teacher_name" column="teacher_name" /> <result property="teacher_number" column="teacher_number" /> <collection property="teacher_student" ofType="student"> <id property="student_id" column="student_id" /> <result property="student_name" column="student_name" javaType="String" /> <result property="student_number" column="student_number" javaType="int" /> </collection> </resultMap> </mapper>
4. 测试
package com.home.mybatis; import java.io.IOException; import org.apache.ibatis.session.SqlSession; import com.home.entity.Student; import com.home.entity.Teacher; public class TestApp { public static void main(String[] args) throws IOException { // 我将获取session的代码封装成了一个工具类,直接用工具类来获取session SqlSession session = SessionUtils.getSession("mybatis.xml"); String loadTeacher="com.home.entity.teacherMapper.loadTeacher"; String loadStudent="com.home.entity.studentMapper.loadStudent"; Teacher teacher = session.selectOne(loadTeacher,1); Student student = session.selectOne(loadStudent,1); System.out.println(student); System.out.println(teacher); // 将数据属性到数据中去 session.commit(); // 关闭session session.close(); } }
5.结果
Student [student_id=4, student_name=hpc, student_number=1, student_teacher=Teacher [teacher_id=1, teacher_name=王老师, teacher_number=1, teacher_student=[]]] Teacher [teacher_id=1, teacher_name=王老师, teacher_number=1, teacher_student=[Student [student_id=5, student_name=zll, student_number=2, student_teacher=null], Student [student_id=4, student_name=hpc, student_number=1, student_teacher=null]]]
mybatis学习笔记三(关联关系)
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