019.动态SQL

1.什么是动态SQL

 

 2.在pom.xml中添加

    <select id="dynamicSQL" parameterType="java.util.Map" resultType="com.imooc.mybatis.entity.Goods">
        select * from t_goods
        <where>
          <if test="categoryId != null">
              and category_id = #{categoryId}
          </if>
          <if test="currentPrice != null">
              and current_price &lt; #{currentPrice}
          </if>
        </where>
    </select>

3.测试类MybatisTest.java

/**
     * 动态SQL语句
     * @throws Exception
     */
    @Test
    public void testDynamicSQL() throws Exception {
        SqlSession session = null;
        try{
            session = MyBatisUtils.openSession();
            Map param = new HashMap();
            param.put("categoryId", 44);
            param.put("currentPrice", 500);
            //查询条件
            List<Goods> list = session.selectList("goods.dynamicSQL", param);
            for(Goods g:list){
                System.out.println(g.getTitle() + ":" +
                        g.getCategoryId()  + ":" + g.getCurrentPrice());

            }
        }catch (Exception e){
            throw e;
        }finally {
            MyBatisUtils.closeSession(session);
        }
    }