mybatis #{}和${}的區別、傳參、基本語法

1 #{}和${}的區別、及注入問題

(1) 區別：
    首先清楚一點，動態 SQL 是 mybatis 的強大特性之一，在 mapper 中定義的參數傳到 xml 中之後，在查詢之前 mybatis 會對其進行動態解析，#{} 和 ${} 在預編譯中的處理是不一樣的：
    例如：select * from t_user where userName = #{name};
    #{}預編譯：用一個佔位符 ? 代替參數:select * from t_user where userName = ?
    #{}預編譯：會將參數值一起進行編譯：select * from t_user where userName = 'zhangsan'
(2) 使用場景：
    一般情況首選#{}，因爲這樣能避免sql注入；如果需要傳參 動態表名、動態字段名時，需要使用${}
    比如：select * from ${tableName} where id > #{id};
(3) SQL注入問題：
    舉個例子，如果使用${}出現的注入問題：
    select * from ${tableName};
    如果傳參 t_user;delete from t_user，則預編譯後的sql如下，將會導致系統不可用：
    select * from t_user;delete from t_user;
(4) like 語句防注入：
    使用concat函數：
    select * from t_user where name like concat('%', #{name}, '%') 
​

2 mybatis幾種傳參方式

非註解：
(1)單參數：
public User getUserByUuid(String uuid); 
<select id="getUserByUuid"  resultMap="BaseResultMap" parameterType="Object">
    SELECT * FROM   t_user  WHERE  uuid = #{uuid}
</select>
(2)多參數
public User getUserByNameAndPass(String name,String pass);  
<select id="getUserByNameAndPass"  resultMap="BaseResultMap" parameterType="Object">
    SELECT * FROM t_user  WHERE  t_name = #{0} and t_pass = #{1}
</select>
(3)Map參數
public User getUserByMap(Map<String,Object> map);
<select id="getUserByMap"  resultMap="BaseResultMap" parameterType="java.util.Map">
    SELECT * FROM t_user  WHERE  t_name = #{name} and t_pass = #{pass}
</select>
(4)實體對象參數
public int updateUser(User user);   
<select id="updateUser"  resultMap="BaseResultMap" parameterType="Object">
    update t_user set t_name = #{name}, t_pass = #{pass} where uuid=#{uuid}
</select>
(4)List集合參數
public int batchDelUser(List<String> uuidList);
<delete id="batchDelUser" parameterType="java.util.List">
    DELETE FROM t_user WHERE uuid IN
    <foreach collection="list" index="index" item="uuid" open="(" separator="," close=")">
        #{uuid}
    </foreach>
</delete>
註解：
public List<User> getUserByTime(@Param("startTime")String startTime, @Param("endTime")String endTime);
<select id="getUserByTime" resultMap="BaseResultMap"  parameterType="Object">
    SELECT * from t_user where createTime &gt;= #{startTime} and createTime &lt;= #{endTime}
</select>
    

2 choose when otherwise

//JAVA 代碼
public List<Group> getUserRoleRelByUserUuid(@Param("groupUuid") String userUuid,@Param("roleList")List<String> roleUuidList);
//SQL
SELECT * from user_role where groupUuid=#{groupUuid}
    <choose>
        <when test="roleList!=null&amp;&amp;roleList.size()&gt;0">
            AND roleUuid IN
            <foreach collection="roleList" index="index" item="roleUuid" open="(" separator="," close=")">
                #{roleUuid}
            </foreach>
        </when>
        <otherwise>
            AND roleUuid IN ('')
        </otherwise>
    </choose>

3 判斷字符串相等

//JAVA 代碼
public int getOrderCountByParams(Map<String, Object> params);
//SQL
<select id="getOrderCountByParams" resultType="java.lang.Integer"  parameterType="Object">
    SELECT count(*) FROM itil_publish_order where 1=1
       <if test="timeType == '1'.toString()" >
            AND create_time &gt;= #{timeStr}
        </if>
        <if test="timeType == '2'.toString()" >
            AND end_time &lt;= #{timeStr}
        </if>
  </select>
或者
<if test = 'timeType== "1"'> </if>

4 CONCAT函數實現 模糊匹配

<select id="getMaxSerialCode" resultType="java.lang.String"  parameterType="Object">
        SELECT count(*) FROM
        itil_publish_order
        WHERE serial_code LIKE CONCAT('%',#{codeStr},'%')
        ORDER BY serial_code DESC LIMIT 1
</select>
​

5 大於等於、小於等於

//JAVA代碼
public List<PublishOrder> getOrderCount(@Param("startTime") String startTime,@Param("startTime")List<String> startTime);
//SQL
<select id="getOrderCount" resultType="java.lang.String"  parameterType="Object">
        SELECT * FROM itil_publish_order
        WHERE createTime &gt;= #{startTime} and &lt;= #{startTime}
</select>