Mybatis学习笔记11 - 动态sql之trim标签

trim标签体中是整个字符串拼串后的结果。
prefix="" 前缀: prefix给拼串后的整个字符串加一个前缀
prefixOverrides="" 前缀覆盖: 去掉整个字符串前面多余的字符
suffix="" 后缀: 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

示例代码：

接口定义：
package com.mybatis.dao;

import com.mybatis.bean.Employee;

import java.util.List;

public interface EmployeeMapper {
    public List<Employee> getEmpsByConditionTrim(Employee employee);
}

mapper定义：
<?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">
<mapper namespace="com.mybatis.dao.EmployeeMapper">
    <!-- 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 -->
    <!-- public List<Employee> getEmpsByConditionTrim(Employee employee); -->
    <select id="getEmpsByConditionTrim" resultType="com.mybatis.bean.Employee">
        select * from tbl_employee
        <!--
        后面多出的and或者or where标签不能解决
        trim标签体中是整个字符串拼串后的结果。
	 	prefix="" 前缀：prefix给拼串后的整个字符串加一个前缀
	 	prefixOverrides="" 前缀覆盖: 去掉整个字符串前面多余的字符
	 	suffix="" 后缀 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
	 	-->
        <!-- 自定义字符串的截取规则 -->
        <trim prefix="where" prefixOverrides="and">
            <if test="id!=null">
                id=#{id}
            </if>
            <if test="lastName!=null && lastName!=''">
                and last_name like #{lastName}
            </if>
            <if test="email!=null and email.trim()!=""">
                and email=#{email}
            </if>
            <if test="gender==0 or gender==1">
                and gender=#{gender}
            </if>
        </trim>
    </select>
</mapper>

测试代码：
package com.mybatis.demo;

import com.mybatis.bean.Employee;
import com.mybatis.dao.EmployeeMapper;
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;

public class MyTest {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void test() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession(true);
        try {
            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
            List<Employee> emps = mapper.getEmpsByConditionTrim(new Employee(null, "jetty", "jetty@126.com", 1));
            for (Employee emp : emps) {
                System.out.println(emp);
            }
        } finally {
            openSession.close();
        }
    }
}