【MyBatis】2、MyBatis 的动态 SQL 和增删改操作

一、添加

(1) 基本插入

<mapper namespace="student">
    <insert id="insert" parameterType="com.pojo.po.Student">
        INSERT INTO student(name, money) VALUES (#{name}, #{money})
    </insert>
</mapper>

public class TestStudent {
    @Test
    public void testInsert() {
        try (SqlSession sqlSession = MyBatisUtil.openSession(true)) {
            Student student = new Student();
            student.setName("鹿晗");
            student.setMoney(100L);
            sqlSession.insert("student.insert", student);
        }
    }
}

注意：openSession() 的参数默认值是 false（不自动提交事务）

(2) 设置新插入记录的主键（id）★

🌼 设置新插入记录的主键（id）到参数对象中

<mapper namespace="student">
    <insert id="insert2" parameterType="com.pojo.po.Student">
        INSERT INTO student(name, money) VALUES (#{name}, #{money})

        <!-- resultType 需要和参数对象的主键的属性名的类型一样 -->
        <!-- keyProperty 是属性名, 不是字段名 -->
        <!-- order="AFTER" 插入语句执行完毕后才查询 -->
        <selectKey resultType="long" keyProperty="id" order="AFTER">
            SELECT LAST_INSERT_ID()
        </selectKey>
    </insert>
</mapper>

二、更新

<mapper namespace="student">
    <update id="update" parameterType="com.pojo.po.Student">
        UPDATE student SET money = #{money} WHERE name = #{name}
    </update>
</mapper>

三、删除

<mapper namespace="student">
    <delete id="delete">
        DELETE FROM student WHERE id in ${ids}
    </delete>
</mapper>

public class TestStudent {

    @Test
    public void testDelete() {
        try (SqlSession sqlSession = MyBatisUtil.openSession(true)) {

            String ids = "(4, 9, 6)";

            sqlSession.insert("student.delete", ids);
        }
    }
    
}

四、动态 SQL

动态 SQL 官方文档：https://mybatis.org/mybatis-3/zh/dynamic-sql.html

(1) if 标签

<mapper namespace="student">
    <select id="dynamicSQL" resultType="com.pojo.po.Student">
        SELECT
        *
        FROM
        student
        WHERE 1 = 1
        <if test="id != null and id > 0">
            AND id > #{id}
        </if>

        <if test="money != null">
            AND money > #{money}
        </if>

        <if test="name != null">
            AND NAME LIKE #{name}
        </if>
    </select>
</mapper>

public class TestStudent {

    @Test
    public void dynamicSql() {
        try (SqlSession sqlSession = MyBatisUtil.openSession(true)) {

            HashMap<String, Object> pMap = new HashMap<>();
            pMap.put("id", 3);
            pMap.put("name", "%杰%");
            // pMap.put("money", 5555);

            List<Student> list = sqlSession.selectList("student.dynamicSQL", pMap);

            for (Student student : list) {
                System.out.println("dynamicSql student = " + student);
            }
        }
    }

}

(2) where 标签

<mapper namespace="student">
    <select id="dynamicSQL" resultType="com.pojo.po.Student">
        SELECT
        *
        FROM
        student
        <where>
            <if test="id != null and id > 0">
                id > #{id}
            </if>

            <if test="money != null">
                AND money > #{money}
            </if>

            <if test="name != null">
                AND NAME LIKE #{name}
            </if>
        </where>
    </select>
</mapper>

(3) foreach 标签

☆ 批量插入：

<mapper namespace="student">
    <insert id="batchInsert1" parameterType="List">
        INSERT INTO student (name, money) VALUES
        <foreach collection="list" item="item" separator=",">
            (#{item.name}, #{item.money})
        </foreach>
    </insert>
</mapper>

💦 批量添加的执行效率比多次单个添加的执行效率要高，但是无法获取到新插入的记录的主键
💦 可以使用 useGeneratedKeys 获取新插入的记录的主键。
💦 假如要添加的记录的字段特别多， 批量添加操作生成的 SQL 语句字符串可能会特别长，SQL 语句的长度可能会超过数据库的限制 【分批插入】
💦 如果传进来的参数是 List 类型，collection 的属性值为 list 就可以遍历这个 List
💦 如果传进来的参数是数组，collection 的属性值为 array 就可以遍历这个数组

☆ 批量删除：

<mapper namespace="student">
    <delete id="batchDelete1" parameterType="List">
        DELETE FROM student
        <where>
            id IN (
                <foreach collection="list"
                         separator=","
                         item="item">
                    #{item}
                </foreach>
            )
        </where>
    </delete>
</mapper>

<mapper namespace="student">
    <delete id="batchDelete2">
        DELETE FROM student
        <where>
            id IN
            <foreach collection="array"
                     separator=","
                     open="("
                     close=")"
                     item="item">
                #{item}
            </foreach>
        </where>
    </delete>
</mapper>

五、起别名

● <typeAliases> 标签写在 mybatis-config.xml 核心配置文件的configuration 标签中
● 写在 <settings> 标签的后面
● 用于设置类型的别名（不区分大小写）

六、sql 标签

<mapper namespace="student">
    <!-- 有抽取公共 SQL 语句的作用 -->
    <sql id="sqlListAll">
        SELECT * FROM student
    </sql>

    <resultMap id="resultMapStudent" type="com.pojo.po.Student">
        <id property="id" column="id"/>
        <result property="createTime" column="create_time"/>
    </resultMap>
    <select id="list" resultMap="resultMapStudent">
        <include refid="sqlListAll"/>
    </select>

    <select id="getById" resultType="com.pojo.po.Student">
        <include refid="sqlListAll"/>
        WHERE id = #{id}
    </select>

    <select id="listByIdAndMoney" resultType="com.pojo.po.Student">
        <include refid="sqlListAll"/>
        WHERE id &lt; #{id} OR money >= #{money}
    </select>

    <select id="getByName" resultType="com.pojo.po.Student">
        <include refid="sqlListAll"/>
        WHERE name LIKE #{name}
    </select>

    <select id="dynamicSQL" resultType="com.pojo.po.Student">
        <include refid="sqlListAll"/>
        <where>
            <if test="id != null and id > 0">
                id > #{id}
            </if>

            <if test="money != null">
                AND money > #{money}
            </if>

            <if test="name != null">
                AND NAME LIKE #{name}
            </if>
        </where>
    </select>

</mapper>

七、在 MyBatis 中集成 druid 连接池

① 引入 Maven 依赖

  <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>druid</artifactId>
      <version>1.1.2</version>
  </dependency>

② 创建连接池工厂类并继承 PooledDataSourceFactory 或UnpooledDataSourceFactory；在连接池工厂类的构造方法中设置数据源 dataSource 为 Druid 的数据源实例

/**
 * MyBatis 中集成 Druid 数据库连接池
 */
public class DruidDataSourceFactory extends PooledDataSourceFactory {
    public DruidDataSourceFactory() {
        this.dataSource = new DruidDataSource();
    }
}

③ 在 mybatis-config.xml 文件中配置 Druid 数据源

  <environments default="development">
      <environment id="development">
          <transactionManager type="JDBC"/>
          <dataSource type="com.common.DruidDataSourceFactory">
              <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
              <property name="url"
                        value="jdbc:mysql://localhost:3306/study_mb?useUnicode=true&amp;characterEncoding=utf8"/>
              <property name="username" value="root"/>
              <property name="password" value="root"/>
              <property name="initialSize" value="5"/>
              <property name="maxActive" value="10"/>
              <property name="maxWait" value="5000"/>
          </dataSource>
      </environment>
</environments>

把 druid 数据库连接池的配置放在 druid.properties 文件中

dev.driverClassName=com.mysql.jdbc.Driver
dev.url=jdbc:mysql://localhost:3306/study_mb?useUnicode=true&characterEncoding=utf8
dev.username=root
dev.password=root
dev.initialSize=5
dev.maxActive=10
dev.maxWait=5000

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<environment id="development">
     <!--采用JDBC的事务管理方法-->
     <transactionManager type="JDBC"/>
     <!--采取druid数据库连接池管理连接-->
     <dataSource type="com.common.DruidDataSourceFactory">
         <property name="driverClassName" value="${dev.driverClassName}"/>
         <property name="url" value="${dev.url}"/>
         <property name="username" value="${dev.username}"/>
         <property name="password" value="${dev.password}"/>
         <property name="initialSize" value="${dev.initialSize}"/>
         <property name="maxActive" value="${dev.maxActive}"/>
         <property name="maxWait" value="${dev.maxWait}"/>
     </dataSource>
</environment>

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