SSM_CRUD新手练习（4）修改生成的mapper.xml映射文件

 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。