一、helloworld

  • Teacher ```java public class Teacher {

    private Integer id; private String name; private String course; private String address; private Date birth; //省略get/set/toString/构造器 }

  2. - TeacherDao
  3. ```java
  4. public interface TeacherDao {
  5.     public Teacher getTeacherById(Integer id);
  6. }
  • sql ```xml SELECT * FROM t_teacher WHERE id =2
![image.png](https://cdn.nlark.com/yuque/0/2021/png/2963105/1630913839436-3bcd2360-4304-41f9-97f1-8063230ca3b1.png#clientId=u8cc0ff95-1da8-4&from=paste&height=63&id=uc8a4258b&margin=%5Bobject%20Object%5D&name=image.png&originHeight=63&originWidth=445&originalType=binary&ratio=1&size=3418&status=done&style=none&taskId=u1b6058fe-60ba-45e3-b93a-ed7600acf40&width=445)

- TeacherDao.xml
```xml
<?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.achang.dao.TeacherDao">
    <resultMap id="teacherMap" type="com.achang.bean.Teacher">
        <id property="id" column="id"/>
        <result property="name" column="teacherName"/>
        <result property="course" column="class_name"/>
        <result property="address" column="address "/>
        <result property="birth" column="birth_date"/>
    </resultMap>

    <select id="getTeacherById" resultMap="teacherMap">
        SELECT * FROM t_teacher WHERE id =#{id}
    </select>

</mapper>
  • mybatis_config.xml ```xml 

- test
```java
public class DaoTest {
    SqlSessionFactory factory;

    @Before
    public void initSqlSessionFactory() throws IOException {
        String resource = "mybatis_config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        factory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void test1(){
        SqlSession sqlSession = factory.openSession();
        Teacher teacherById;
        try {
            TeacherDao mapper = sqlSession.getMapper(TeacherDao.class);
            teacherById = mapper.getTeacherById(2);
        } finally {
            sqlSession.close();
        }
        System.out.println(teacherById);
        //Teacher{id=2, name='张飞', course='数学', address='鹿城区', birth=Wed Sep 16 00:00:00 CST 2020}
    }

}

二、if标签

  • TeacherDao.xml

因为在xml文件中编写，会有歧义，需要使用转义符还区别各种符号

<?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.achang.dao.TeacherDao">
    <resultMap id="teacherMap" type="com.achang.bean.Teacher">
        <id property="id" column="id"/>
        <result property="name" column="teacherName"/>
        <result property="course" column="class_name"/>
        <result property="address" column="address "/>
        <result property="birth" column="birth_date"/>
    </resultMap>

    <select id="getTeacherByCondition" resultMap="teacherMap">
        SELECT * FROM t_teacher WHERE
        <!--test属性：指定编写判断条件
            id!=null：取出传入的javabean属性中id的值，判断其是否为空
        -->
        <if test="id!=null">
            id > #{id} and
        </if>
        <if test="name!=null and !name.equals(&quot;&quot;) ">
            teacherName like #{name} and
        </if>
        <if test="birth!=null">
            birth_date &lt; #{birth}
        </if>
    </select>

</mapper>
  • TeacherDao ```java public interface TeacherDao { //找到满足传入teacher对象中设置值条件的集合 public List getTeacherByCondition(Teacher teacher); }

- DaoTest
```java
public class DaoTest {
    SqlSessionFactory factory;

    @Before
    public void initSqlSessionFactory() throws IOException {
        String resource = "mybatis_config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        factory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void test1(){
        SqlSession sqlSession = factory.openSession();
        Teacher teacherById;
        try {
            TeacherDao mapper = sqlSession.getMapper(TeacherDao.class);
            Teacher teacher = new Teacher();

            //给teacher对象属性set值，代表传入值，对应上面的不为null
            teacher.setId(1);
            teacher.setName("%a%");
            teacher.setBirth(new Date());

            List<Teacher> teacherByCondition = mapper.getTeacherByCondition(teacher);
            for (Teacher teacher1:teacherByCondition){
                System.out.println(teacher1);
                //Teacher{id=3, name='tomcat', course='英语', address='瑞安县', birth=Fri Jun 30 00:00:00 CST 2017}
            }
        } finally {
            sqlSession.close();
        }
    }

}

三、where标签

我们的查询语句就放在where标签内，每一个and放在前面

<?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.achang.dao.TeacherDao">
    <resultMap id="teacherMap" type="com.achang.bean.Teacher">
        <id property="id" column="id"/>
        <result property="name" column="teacherName"/>
        <result property="course" column="class_name"/>
        <result property="address" column="address "/>
        <result property="birth" column="birth_date"/>
    </resultMap>

    <select id="getTeacherByCondition" resultMap="teacherMap">
        SELECT * FROM t_teacher
        <!--where标签：可以帮我们去除掉前面的and-->
        <where>
            <if test="id!=null">
                id > #{id}
            </if>
            <if test="name!=null and !name.equals(&quot;&quot;) ">
                and teacherName like #{name}
            </if>
            <if test="birth!=null">
                and birth_date &lt; #{birth}
            </if>
        </where>
    </select>

</mapper>

四、trim标签

<?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.achang.dao.TeacherDao">
    <resultMap id="teacherMap" type="com.achang.bean.Teacher">
        <id property="id" column="id"/>
        <result property="name" column="teacherName"/>
        <result property="course" column="class_name"/>
        <result property="address" column="address "/>
        <result property="birth" column="birth_date"/>
    </resultMap>

    <select id="getTeacherByCondition" resultMap="teacherMap">
        SELECT * FROM t_teacher
        <!--截取字符串
        prefix属性：为下面的sql整体添加一个前缀
        prefixOverrides属性：取出整体字符串钱多多余的字符
        suffix：为整体添加一个后缀
        suffixOverrides：后面哪个多了可以去掉
        -->
        <trim prefix="where" prefixOverrides="and">
            <if test="id!=null">
                id > #{id}
            </if>
            <if test="name!=null and !name.equals(&quot;&quot;) ">
                and teacherName like #{name}
            </if>
            <if test="birth!=null">
                and birth_date &lt; #{birth}
            </if>
        </trim>
    </select>

</mapper>

五、foreach遍历元素

  • TeacherDao ```java public interface TeacherDao { public List getTeacherByIdIn(@Param(“ids”) List ids); }

- TeacherDao.xml
```xml
<?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.achang.dao.TeacherDao">
    <resultMap id="teacherMap" type="com.achang.bean.Teacher">
        <id property="id" column="id"/>
        <result property="name" column="teacherName"/>
        <result property="course" column="class_name"/>
        <result property="address" column="address "/>
        <result property="birth" column="birth_date"/>
    </resultMap>

    <select id="getTeacherByIdIn" resultMap="teacherMap">
        SELECT * FROM t_teacher WHERE id IN
        <!--foreach遍历集合
            collection属性：指定要遍历集合的key
            close属性：以书什么结束
            item属性：每次遍历的元素，命名任意，方便引用
            index属性：
                如果遍历的是一个list，指定变量保存的当前元素的索引
                    item为值
                如果遍历的是一个map，指定变量保存的当前元素的key
                    item为value值
            open属性：以什么开始
            separator属性：每次遍历元素的分隔符
        -->
        <foreach collection="ids" close=")" item="id_item" open="(" separator=",">
            #{id_item}
        </foreach>
    </select>

</mapper>

  • test ```java public class DaoTest { SqlSessionFactory factory; @Before public void initSqlSessionFactory() throws IOException {

      String resource = "mybatis_config.xml";
  InputStream inputStream = Resources.getResourceAsStream(resource);
  factory = new SqlSessionFactoryBuilder().build(inputStream);

    }

    @Test public void test1(){

      SqlSession sqlSession = factory.openSession();
  Teacher teacherById;
  try {
      TeacherDao mapper = sqlSession.getMapper(TeacherDao.class);
      List<Teacher> teacherByIdIn = mapper.getTeacherByIdIn(Arrays.asList(1, 2, 3, 4, 5));
      for (Teacher teacher:teacherByIdIn){
          System.out.println(teacher);
          //Teacher{id=1, name='admin', course='语文', address='龙湾区', birth=Thu Dec 17 00:00:00 CST 2020}
          //Teacher{id=2, name='张飞', course='数学', address='鹿城区', birth=Wed Sep 16 00:00:00 CST 2020}
          //Teacher{id=3, name='tomcat', course='英语', address='瑞安县', birth=Fri Jun 30 00:00:00 CST 2017}
      }
  } finally {
      sqlSession.close();
  }

    }

}

<a name="G2faJ"></a>
## 六、choose标签
when标签：设置情况；满足后其他情况跳过<br />otherwise标签：当所有都不情况都不满足时，就执行此标签<br />类似ifelse-else

- TeacherDao
```java
public interface TeacherDao {
   public List<Teacher> getTeacherByConditionChoose(Teacher teacher);
}

  • TeacherDao.xml ```xml <?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">



- test
```java
public class DaoTest {
    SqlSessionFactory factory;

    @Before
    public void initSqlSessionFactory() throws IOException {
        String resource = "mybatis_config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        factory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void test1(){
        SqlSession sqlSession = factory.openSession();
        Teacher teacherById;
        try {
            TeacherDao mapper = sqlSession.getMapper(TeacherDao.class);
            Teacher teacher = new Teacher();
            teacher.setId(2);
            teacher.setName("admin");
            List<Teacher> teacherByConditionChoose = mapper.getTeacherByConditionChoose(teacher);
        } finally {
            sqlSession.close();
        }
    }

}

七、set标签

用于SQL语句中的update操作

  • sql ```xml UPDATE t_teacher SET teacherName=?, class_name=?, address=?, birth_date=? WHERE id=?

- TeaherDao
```java
public interface TeacherDao {
    public int updateTeacher(Teacher teacher);
}

  • TeaherDao.xml ```xml <?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">

    UPDATE t_teacher teacherName=#{name}, class_name=#{course}, address=#{address}, birth_date=#{birth} id=#{id} 


- test
```java
public class DaoTest {
    SqlSessionFactory factory;

    @Before
    public void initSqlSessionFactory() throws IOException {
        String resource = "mybatis_config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        factory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void test1(){
        //开始自动提交事务
        SqlSession sqlSession = factory.openSession(true);
        Teacher teacherById;
        try {
            TeacherDao mapper = sqlSession.getMapper(TeacherDao.class);
            Teacher teacher = new Teacher();
            teacher.setId(2);
            teacher.setName("admin");
            int i = mapper.updateTeacher(teacher);
            System.out.println(i);
        } finally {
            sqlSession.close();
        }
    }
}

八、bind标签【不推荐】

  • bind 元素可以从 OGNL 表达式中创建一个变量并将其绑定到上下文。比如：

后期更改匹配规则麻烦

例如：设置调用myLastName时前后默认添加%
image.png

九、OGNL表达式

  • OGNL（ Object Graph Navigation Language ）对象图导航语言（类似级联属性）
  • 这是一种强大的表达式语言，通过它可以非常方便的来操作对象属性。类似于我们的EL，SpEL等

image.png
image.png