[mybatis]动态sql_if_where_trim判断&OGNL

Posted 2022-02-11 唐火

OGNL

if

要求：查询员工，要求，携带了哪个字段查询条件就带上这个字段的值

  //携带了哪个字段查询条件就带上这个字段的值
    public List<Employee> getEmpsByConditionIf(Employee employee);

<!--    public List<Employee> getEmpsByConditionIf(Employee employee);-->
<select id="getEmpsByConditionIf" resultType="com.atguigu.mybatis.bean.Employee">
    select * from tb1_employee
    where
    <!--test,判断表达式(OGNL)
      OGNL参照PPT或者官方文档
      c:if test

      从参数中取值进行判断
      遇见特殊符号应该去写转义字符;
      -->

    <if test = "id!=null">
        id = #id
    </if>

    <if test = "lastName!=null &amp;&amp; lastName!=&quot;&quot;">

        and last_name like #lastName

    </if>
<if test="email!=null and email.trim()!=&quot;&quot;">

    and email = #email
</if>


<!--ognl会进行字符串与数字的转换判断  "0"==0  -->
<if test="gender==0 or gender==1">
    and gender = #gender

</if>


</select>

    @Test
    public void test04() throws IOException 
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();

        SqlSession sqlSession = sqlSessionFactory.openSession();

        try
        
            EmployeeMapperDynamicSQL mapper = sqlSession.getMapper(EmployeeMapperDynamicSQL.class);


            Employee employee = new Employee(3,"%e%","[e-mail]",null);

            List<Employee> emps = mapper.getEmpsByConditionIf(employee);

            for (Employee emp:emps)
            
                System.out.println(emp);
            

        finally 

            sqlSession.close();

        
    

• 查询的时候，如果某些条件没带，sql的拼装可能出现问题

解决方法，使用where

where

• 第一种方法

给where后面加上1=1，以后的条件都and xxx

• 第二种方法

mybatis使用where标签来将所有的查询条件包括在内。mybatis就会将where标签中拼接的sql，多出来的and或者or去掉，where只会去掉第一个多出来的and或者or。

<!--    public List<Employee> getEmpsByConditionIf(Employee employee);-->
<select id="getEmpsByConditionIf" resultType="com.atguigu.mybatis.bean.Employee">
    select * from tb1_employee
    <where>


        <if test = "id!=null">
            id = #id
        </if>

        <if test = "lastName!=null &amp;&amp; lastName!=&quot;&quot;">

            and last_name like #lastName

        </if>
        <if test="email!=null and email.trim()!=&quot;&quot;">

            and email = #email
        </if>


        <!--ognl会进行字符串与数字的转换判断  "0"==0  -->
        <if test="gender==0 or gender==1">
            and gender = #gender

        </if>
        
        
    </where>



</select>

trim

后面多出的and或者or where标签不能解决

• prefix = “”:前缀;trim标签体中整个字符串拼串后的结果。
• prefix给拼串后的整个字符串加一个前缀
• prefixOverrides = “”:前缀覆盖;去掉整个字符串多余的字符
• suffix = “”:给拼串后的整个字符串加一个后缀
• suffixOverrides = “”:后缀覆盖；去掉整个字符串后面多余的字符

<!--    public List<Employee> getEmpsByConditionIf(Employee employee);-->
<select id="getEmpsByConditionIf" resultType="com.atguigu.mybatis.bean.Employee">
    select * from tb1_employee
    <trim prefix="where" suffixOverrides="and">


        <if test = "id!=null">
            id = #id and
        </if>

        <if test = "lastName!=null &amp;&amp; lastName!=&quot;&quot;">

             last_name like #lastName and

        </if>
        <if test="email!=null and email.trim()!=&quot;&quot;">

             email = #email and
        </if>


        <!--ognl会进行字符串与数字的转换判断  "0"==0  -->
        <if test="gender==0 or gender==1">
             gender = #gender

        </if>


    </trim>



</select>