技術標籤：Mybatismysqlsqljava

文章目錄

• 1. 測試環境搭建
• 2. 例項測試

本文章涉及環境版本：

• mysql 5.7
• Mybatis 3.5.x
• Maven 3.6.x
• JDK 1.8

專案程式碼倉庫：
https://github.com/Gang-bb/Study-Record/tree/main/bzhan-mybatis-study
需要clone整個bzhan-mybatis-study專案
(整體是一個maven多module工程)
該文章對應：《bzhan-mybatis-study06 》module專案

1. 測試環境搭建

主要關鍵類程式碼修改：

@Data
@NoArgsConstructor
 

@AllArgsConstructor
public class Student {
    private Integer id;
    private String name;
   	private Integer tid;
}

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Teacher {
    private Integer id;
    private String name;
    
    private List<Student> students;
}

2. 例項測試

查詢教師及其所有學生

方式一：按照結果巢狀處理

1. TeacherMapper

Teacher getTeacher();

2. TeacherMapper.xml

<!--按結果巢狀查詢-->
<select id="getTeacher" resultMap="TeacherStudent">
    select s.id sid, s.name sname, t.name tname,t.id tid
    from student s,teacher t
    where s.tid = t.id and t.id = #{tid}
</
 
select>

<resultMap id="TeacherStudent" type="Teacher">
    <result property="id" column="tid"/>
    <result property="name" column="tname"/>
    <!--複雜的屬性，我們需要單獨處理 物件： association 集合： collection
    javaType="" 指定屬性的型別！
    集合中的泛型資訊，我們使用ofType獲取
    -->
    <collection property="students" ofType="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <result property="tid" column="tid"/>
    </collection>
</resultMap>

3. 測試類

@Test
public void getTeacher(){
    SqlSession sqlSession = null;
    try {
        sqlSession = MybatisUtil.openSession();
        TeacherMapper teacherMapper = sqlSession.getMapper(TeacherMapper.class);

        System.out.println(teacherMapper.getTeacher(1));
    } finally {
        sqlSession.close();
    }
}

4. 結果

方式二：按照查詢巢狀處理

1. TeacherMapper

Teacher getTeacher2();

2. TeacherMapper.xml

<!-- 一對多模型 按照查詢巢狀處理-->
<select id="getTeacher2" resultMap="TeacherStudent2">
    select id, name from teacher where id = #{id}
</select>

<resultMap id="TeacherStudent2" type="Teacher">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
    <collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"/>
</resultMap>

<select id="getStudentByTeacherId" resultType="Student">
    select * from student where tid = #{tid}
</select>

3. 測試類

@Test
public void getTeacher(){
    SqlSession sqlSession = null;
    try {
        sqlSession = MybatisUtil.openSession();
        TeacherMapper teacherMapper = sqlSession.getMapper(TeacherMapper.class);

        System.out.println(teacherMapper.getTeacher2(1));
    } finally {
        sqlSession.close();
    }
}

4. 結果

注意點：

• 保證SQL的可讀性，儘量保證通俗易懂
• 注意一對多和多對一中，屬性名和欄位的問題！