MyBatis3_[tp_38~]_动态sql_if_判断&OGNL_where标签_

笔记要点
出错分析与总结

/** 笔记:
 *  查询的时候,如果某些条件,没带可能SQL拼装会有问题;
 *      1.-->给where 后面加上 1=1, 以后的条件都and XXX
 *      2. <where> </where> 标签加上后,就不用写SQL的 where 条件语句!
 */

工程组织
数据库组织

0.重新修改Bean类
1.定义接口 

EmployeeMapper_DynamicSQL

package com.dao;

import com.bean.Employee;

import java.util.List;

public interface EmployeeMapper_DynamicSQL {
    public Employee getEmpsByConditionIf(int id);
    public List<Employee> getEmpsByConditionIf(Employee e);
}

2.定义XML映射文件

<?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">
        <!--动态SQL几个主要模块:-->
        <!--if 标签
             test="判断表达式,OGNL语法(参照PPT)"
              :从传入的参数中取值判断,
              遇见特殊符号,写转义字符!-> and : &amp;&amp;  "" : &quot;&quot;
                    或者写单引号也可以!!
                    网址: W3CSchool->html教程->ISO-8859-> ASCII编码
             OGNL : 会进行字符串与数字的转换判断 "0"==0 ,"1"==1 ;
        -->
        <!--where 标签
             查询的时候,如果某些条件,没带可能SQL拼装会有问题;
             给where 后面加上 1=1, 以后的条件都and XXX
             2.mybatis 使用where 标签来将所有的查询条件包含在内,
                    自动去掉拼接后的SQL 的前面的多出来的and 或者or ;在后面的就不可以了!
        -->
        <!--choose (when, otherwise)-->
        <!--trim (where, set)-->
        <!--foreach-->
<mapper namespace="com.dao.EmployeeMapper_DynamicSQL">
    <!--1.查询员工,要求,携带了那个字段查询条件就带上那个条件的值;
            传入两个条件进行模糊查询-->
    <select id="getEmpsByConditionIf" resultType="com.bean.Employee">
        select * from tbl_employee

        <where>
            <if test="lastName !=null and lastName !='jerry' ">
               and last_name like #{lastName}
            </if>
            <if test="id != null">
                and  id=#{id}
            </if>
      </where>
</select>

</mapper>

3.编写测试代码

package com.test;

import com.bean.Employee;
import com.dao.EmployeeMapper_DynamicSQL;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

/** 笔记:
 *  查询的时候,如果某些条件,没带可能SQL拼装会有问题;
 *      1.-->给where 后面加上 1=1, 以后的条件都and XXX
 *      2. <where> </where> 标签加上后,就不用写SQL的 where 条件语句!
 */
public class test_tp38 {
        public SqlSessionFactory getSqlSessionFactory() throws IOException {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            return new SqlSessionFactoryBuilder().build(inputStream);
        }

        @Test
        public void test08() throws Exception {

            SqlSession openSession = getSqlSessionFactory().openSession();
            try {
                System.out.println("++++++++++---- 1.测试 动态SQL元素:if关键字!");
                EmployeeMapper_DynamicSQL mapper = openSession.getMapper(EmployeeMapper_DynamicSQL.class);
                Employee employee = new Employee(1, "%e%", null, null);
                List<Employee> emps = mapper.getEmpsByConditionIf(employee);
                for (Employee e:emps)
                    System.out.println(e);
                openSession.commit();
            } finally {
                openSession.close();
            }

        }

}

测试结果:

++++++++++---- 1.测试 动态SQL元素:if关键字!
DEBUG 12-04 16:18:20,585 ==>  Preparing: select * from tbl_employee WHERE last_name like ? and id=?   (BaseJdbcLogger.java:145) 
DEBUG 12-04 16:18:20,608 ==> Parameters: %e%(String), 1(Integer)  (BaseJdbcLogger.java:145) 
DEBUG 12-04 16:18:20,620 <==      Total: 1  (BaseJdbcLogger.java:145) 
Employee{id=1, lastName='jerry', email='jerry@163.com', gender='1', dept=null}