mybatis the handling of many-to-learn 6____

This case is a maven project:

1. build a database environment:

Environmental data corresponding to more than one student is a teacher:

CREATE TABLE `teacher` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8

INSERT INTO teacher(`id`, `name`) VALUES (1, '秦老师'); 

CREATE TABLE `student` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  `tid` INT(10) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fktid` (`tid`),
  CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8


INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('1' , ' Military students ' , ' . 1 ' ); 
 the INSERT  the INTO `student` (id``, `name`,` tid`) the VALUES ( ' 2 ' , ' LiTongXue ' , ' . 1 ' ); 
 the INSERT  the INTO `Student `(` id`, `name`,` tid`) the VALUES ( ' . 3 ' , ' military students ' , ' . 1 ' ); 
 the INSERT  the INTO `student` (id``, `name`,`tid`) VALUES ( '4 ' , ' Yao students ' , ' 1 ' ); 
 the INSERT  the INTO `student` (id``, `name`,` tid`) the VALUES ( ' . 5 ' , ' summer students ' , ' 1 ' );

Requirements: Requirements to get all the student's name, student number, corresponding to the teacher's name. (Note: involves two tables)

2. student's pojo entity classes:

public  class Student {
     Private  int ID;
     Private String name;
     Private  int TID;
     Private Teacher Teacher;
        // note corresponding to a plurality of teacher student 

    public Student () { 
    } 

    public Student ( int ID, String name, int TID, Teacher Teacher) {
         the this .id = ID;
         the this .name = name;
         the this .tid = TID;
         the this .teacher = Teacher; 
    } 

    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 int getTid() {
        return tid;
    }

    public void setTid(int tid) {
        this.tid = tid;
    }

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", tid=" + tid +
                ", teacher=" + teacher +
                '}';
    }
}

3.Dao layer write StudentMapper interface:

public  interface StudentDAO { 
     // 1;
     // get all students
     // by way of a database, a table lookup even 
    List <Student> getStudents ();      // Method two: 

    

    // get all students
     // is the object-oriented manner, query 
    List <Student> getStudents2 (); 

}

Write 4.StudentMapper.xml file:

<?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.xbf.dao.StudentDao">
    <select id="getStudents" resultMap="StudentTeacher">
        select * from student
    </select>

    <resultMap id="StudentTeacher" type="Student">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <association column="tid" property="teacher" javaType="Teacher" select="getTeacherName"/>
    </resultMap>

    <select id="getTeacherName" resultType="Teacher">
        select name from teacher where id=#{id}
    </select>


    <!--cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc-->
    <select id="getStudents2" resultMap="StudentTeacher2">
        select s.id,s.name,t.name as tname from student s,teacher t where s.tid=t.id
    </select>

    <resultMap id="StudentTeacher2" type="Student">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <association property="teacher" javaType="Teacher">
            <result property="name" column="tname"></result>
        </association>
    </resultMap>



</mapper>

Core write 5.mybatis-config.xml file:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <properties resource="database.properties"/>
    
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

    <typeAliases>
        <package name="com.xbf.pojo"></package>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>

            </dataSource>
        </environment>
    </environments>


    <mappers>
       <mapper resource="com/xbf/dao/teacherMapper.xml"></mapper>
    </mappers>

</configuration>

6. Test preparation classes:

public class StudentDaoTest {

    @Test
    public void getStudents(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        List<Student> students = mapper.getStudents();
        for (Student student : students) {
            System.out.println(student.getName()+student.getTeacher().getName());
        }
    }

    @Test
    public void getStudents2(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        List<Student> students = mapper.getStudents2();
        for (Student student : students) {
            System.out.println(student.getName()+student.getTeacher().getName());
        }
    }
}

to sum up:

mybatis in the case of many-to get in StudentMapper.xml (corresponding to the interface configuration file) use assosiation label, there are two ways to solve the problem:

Method 1: Use connections to the database table query;

Method 2: Use object associated object-oriented.