MyBatis的Mapper映射文件详解

<?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"><!--    namespace:命名空间,接口的全类名    id:唯一标示    resultType:返回值类型    #{id}:从传递过来的参数中取出id的值   --><mapper namespace="com.flx.mybatis.guigu.employee.dao.EmployeeMapper">    <!--Map传参-->    <select id="getEmployeeByParamMap" resultType="com.flx.mybatis.guigu.bean.Employee" databaseId="mysql">        select * from tb1_employee where id=#{id} and last_name=#{lastName}    </select>    <!--注解支持的传参-->    <select id="getEmployeeByIdAndLastName" resultType="com.flx.mybatis.guigu.bean.Employee" databaseId="mysql">        select * from tb1_employee where id=#{id} and last_name=#{lastName}    </select>    <!--这条语句在mysql环境下面使用的，databaseId-->    <select id="getEmployeeById" resultType="com.flx.mybatis.guigu.bean.Employee" databaseId="mysql">        select * from tb1_employee where id = #{id}    </select>    <!--这条语句在oracle环境下面使用的，databaseId-->    <select id="getEmployeeById" resultType="com.flx.mybatis.guigu.bean.Employee" databaseId="oracle">        select emp_id id,emp_name lastName,emp_age age from employee where emp_id = #{id}    </select>    <!--下面写增删改-->    <!--参数类型可以省略-->    <!--支持主键获取        useGeneratedKeys = true 使用自增主键获取值        keyProperty = id 将获得的id放在id属性中    -->    <insert id="addEmployee" parameterType="com.flx.mybatis.guigu.bean.Employee" databaseId="mysql"     useGeneratedKeys="true" keyProperty="id">        insert into tb1_employee (last_name,gender,email)        VALUES (#{lastName},#{gender},#{email})    </insert>    <!--oracle不支持自增，支持序列-->    <insert id="addEmployee" databaseId="oracle">        <!--order: 当前sql在插入sql之前运行-->        <selectKey keyProperty="id" order="BEFORE" resultType="Integer" >            <!--编写查询主键的sql-->            select seq_employee.nextval from dual        </selectKey>        <selectKey keyProperty="id" order="AFTER" resultType="Integer" >            <!--insert语句执行完执行这个-->            select seq_employee.currval from dual        </selectKey>        <!--流程：查询seq序列的sql先执行结果赋值给id，然后执行insert语句时候动态把id传给insert的sql完成主键的存储-->        insert into employee (emp_id,last_name,gender,email)        VALUES (#{id},#{lastName},#{gender},#{email})    </insert>    <update id="updateEmployee" >        update tb1_employee set last_name=#{lastName},gender=#{gender},email=#{email}        where id=#{id}    </update>    <delete id="deleteEmployee">        delete from tb1_employee where id=#{id}    </delete></mapper>