我们为什么要修改呢，这是因为我们查询的时候，我们有时候需要连表查询，例如我们需要查询出员工表的信息(emp_id,emp_name...)与此同时，我们还想查询出该员工所在的部门（dept_name）。此时，生成mapper文件查询的只是表中已有的字段。
所以我们可以在EmployeeMapper.xml中添加两个方法，
同时我们还要为Employee.java添加一个Department属性，别忘记增加setter和getter。
最后我们需要修改EmployeeMapper.xml文件，增加两个连表查询语句：
<?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.atguigu.crud.dao.EmployeeMapper"> <resultMap id="BaseResultMap" type="com.atguigu.crud.bean.Employee"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> <id column="emp_id" jdbcType="INTEGER" property="empId" /> <result column="emp_name" jdbcType="VARCHAR" property="empName" /> <result column="gender" jdbcType="CHAR" property="gender" /> <result column="email" jdbcType="VARCHAR" property="email" /> <result column="d_id" jdbcType="INTEGER" property="dId" /> </resultMap> <resultMap type="com.atguigu.crud.bean.Employee" id="WithDeptResultMap"> <id column="emp_id" jdbcType="INTEGER" property="empId" /> <result column="emp_name" jdbcType="VARCHAR" property="empName" /> <result column="gender" jdbcType="CHAR" property="gender" /> <result column="email" jdbcType="VARCHAR" property="email" /> <result column="d_id" jdbcType="INTEGER" property="dId" /> <association property="department" javaType="com.atguigu.crud.bean.Department"> <id column="dept_id" property="deptId"/> <result column="dept_name" property="deptName"/> </association> </resultMap> <sql id="Example_Where_Clause"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> <where> <foreach collection="oredCriteria" item="criteria" separator="or"> <if test="criteria.valid"> <trim prefix="(" prefixOverrides="and" suffix=")"> <foreach collection="criteria.criteria" item="criterion"> <choose> <when test="criterion.noValue"> and ${criterion.condition} </when> <when test="criterion.singleValue"> and ${criterion.condition} #{criterion.value} </when> <when test="criterion.betweenValue"> and ${criterion.condition} #{criterion.value} and #{criterion.secondValue} </when> <when test="criterion.listValue"> and ${criterion.condition} <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=","> #{listItem} </foreach> </when> </choose> </foreach> </trim> </if> </foreach> </where> </sql> <sql id="Update_By_Example_Where_Clause"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> <where> <foreach collection="example.oredCriteria" item="criteria" separator="or"> <if test="criteria.valid"> <trim prefix="(" prefixOverrides="and" suffix=")"> <foreach collection="criteria.criteria" item="criterion"> <choose> <when test="criterion.noValue"> and ${criterion.condition} </when> <when test="criterion.singleValue"> and ${criterion.condition} #{criterion.value} </when> <when test="criterion.betweenValue"> and ${criterion.condition} #{criterion.value} and #{criterion.secondValue} </when> <when test="criterion.listValue"> and ${criterion.condition} <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=","> #{listItem} </foreach> </when> </choose> </foreach> </trim> </if> </foreach> </where> </sql> <sql id="Base_Column_List"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> emp_id, emp_name, gender, email, d_id </sql> <sql id="WithDept_Column_List"> e.emp_id, e.emp_name, e.gender, e.email, e.d_id,d.dept_id,d.dept_name </sql> <!-- 带部门的两个查询 --> <select id="selectByExampleWithDept" resultMap="WithDeptResultMap"> select <if test="distinct"> distinct </if> <include refid="WithDept_Column_List" /> from tbl_emp e left join tbl_dept d on e.d_id=d.dept_id <if test="_parameter != null"> <include refid="Example_Where_Clause" /> </if> <if test="orderByClause != null"> order by ${orderByClause} </if> </select> <!-- 带部门的主键查询 --> <select id="selectByPrimaryKeyWithDept" resultMap="WithDeptResultMap"> select <include refid="WithDept_Column_List" /> from tbl_emp e left join tbl_dept d on e.d_id=d.dept_id where emp_id = #{empId,jdbcType=INTEGER} </select> <select id="selectByExample" parameterType="com.atguigu.crud.bean.EmployeeExample" resultMap="BaseResultMap"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> select <if test="distinct"> distinct </if> <include refid="Base_Column_List" /> from tbl_emp <if test="_parameter != null"> <include refid="Example_Where_Clause" /> </if> <if test="orderByClause != null"> order by ${orderByClause} </if> </select> <select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultMap="BaseResultMap"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> select <include refid="Base_Column_List" /> from tbl_emp where emp_id = #{empId,jdbcType=INTEGER} </select> <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> delete from tbl_emp where emp_id = #{empId,jdbcType=INTEGER} </delete> <delete id="deleteByExample" parameterType="com.atguigu.crud.bean.EmployeeExample"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> delete from tbl_emp <if test="_parameter != null"> <include refid="Example_Where_Clause" /> </if> </delete> <insert id="insert" parameterType="com.atguigu.crud.bean.Employee"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> insert into tbl_emp (emp_id, emp_name, gender, email, d_id) values (#{empId,jdbcType=INTEGER}, #{empName,jdbcType=VARCHAR}, #{gender,jdbcType=CHAR}, #{email,jdbcType=VARCHAR}, #{dId,jdbcType=INTEGER}) </insert> <insert id="insertSelective" parameterType="com.atguigu.crud.bean.Employee"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> insert into tbl_emp <trim prefix="(" suffix=")" suffixOverrides=","> <if test="empId != null"> emp_id, </if> <if test="empName != null"> emp_name, </if> <if test="gender != null"> gender, </if> <if test="email != null"> email, </if> <if test="dId != null"> d_id, </if> </trim> <trim prefix="values (" suffix=")" suffixOverrides=","> <if test="empId != null"> #{empId,jdbcType=INTEGER}, </if> <if test="empName != null"> #{empName,jdbcType=VARCHAR}, </if> <if test="gender != null"> #{gender,jdbcType=CHAR}, </if> <if test="email != null"> #{email,jdbcType=VARCHAR}, </if> <if test="dId != null"> #{dId,jdbcType=INTEGER}, </if> </trim> </insert> <select id="countByExample" parameterType="com.atguigu.crud.bean.EmployeeExample" resultType="java.lang.Long"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> select count(*) from tbl_emp <if test="_parameter != null"> <include refid="Example_Where_Clause" /> </if> </select> <update id="updateByExampleSelective" parameterType="map"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> update tbl_emp <set> <if test="record.empId != null"> emp_id = #{record.empId,jdbcType=INTEGER}, </if> <if test="record.empName != null"> emp_name = #{record.empName,jdbcType=VARCHAR}, </if> <if test="record.gender != null"> gender = #{record.gender,jdbcType=CHAR}, </if> <if test="record.email != null"> email = #{record.email,jdbcType=VARCHAR}, </if> <if test="record.dId != null"> d_id = #{record.dId,jdbcType=INTEGER}, </if> </set> <if test="_parameter != null"> <include refid="Update_By_Example_Where_Clause" /> </if> </update> <update id="updateByExample" parameterType="map"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> update tbl_emp set emp_id = #{record.empId,jdbcType=INTEGER}, emp_name = #{record.empName,jdbcType=VARCHAR}, gender = #{record.gender,jdbcType=CHAR}, email = #{record.email,jdbcType=VARCHAR}, d_id = #{record.dId,jdbcType=INTEGER} <if test="_parameter != null"> <include refid="Update_By_Example_Where_Clause" /> </if> </update> <update id="updateByPrimaryKeySelective" parameterType="com.atguigu.crud.bean.Employee"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> update tbl_emp <set> <if test="empName != null"> emp_name = #{empName,jdbcType=VARCHAR}, </if> <if test="gender != null"> gender = #{gender,jdbcType=CHAR}, </if> <if test="email != null"> email = #{email,jdbcType=VARCHAR}, </if> <if test="dId != null"> d_id = #{dId,jdbcType=INTEGER}, </if> </set> where emp_id = #{empId,jdbcType=INTEGER} </update> <update id="updateByPrimaryKey" parameterType="com.atguigu.crud.bean.Employee"> <!-- WARNING - @mbg.generated This element is automatically generated by MyBatis Generator, do not modify. This element was generated on Thu Oct 18 13:46:16 CST 2018. --> update tbl_emp set emp_name = #{empName,jdbcType=VARCHAR}, gender = #{gender,jdbcType=CHAR}, email = #{email,jdbcType=VARCHAR}, d_id = #{dId,jdbcType=INTEGER} where emp_id = #{empId,jdbcType=INTEGER} </update> </mapper>
现在，我们就能查询出带部门信息的员工表了。