SSM框架的(CRUD)基础环境搭建4.0

具体步骤请参考由本文作者编写的另一篇文章《SSM框架配置》

编写SSM整合的关键配置文件

• web.xml，spring，springmvc，mybatis，使用mybatis的逆向工程生成对应的bean以及mapper

修改Mapper文件

查询员工信息的时候，还需要展示部门的名称，逆向生成的mapper中select查询部分只有部门的d_id,所以需要联合查询，提高性能。

<sql id="Base_Column_List">
    emp_id, emp_name, gender, email, d_id
</sql>

步骤一：进入EmployeeMapper.java,新增两个方法

List<Employee> selectByExampleWithDept(EmployeeExample example);
Employee selectByPrimaryKeyWithDept(Integer empId);

步骤二、进入Employee.java

//希望查询员工的同时部门信息也是查询好的
private Department department;
public Department getDepartment() {
    return department;
}
public void setDepartment(Department department) {
    this.department = department;
}

步骤三、进入EmployeeMapper.xml
（1）新建id为WithDeptResultMap的resultMap

<resultMap type="com.christmaseve.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="VARCHAR" property="gender" />
    <result column="email" jdbcType="VARCHAR" property="email" />
    <result column="d_id" jdbcType="INTEGER" property="dId" />
    <!-- 指定联合查询出的部门字段的封装 -->
    <association property="department" javaType="com.christmaseve.crud.bean.Department">
        <id column="dept_id" property="deptId"/>
        <result column="dept_name" property="deptName"/>
    </association>
</resultMap>

（2）新建id为WithDept_Base_Column_List的sql

<sql id="WithDept_Base_Column_List">
    e.emp_id, e.emp_name, e.gender, e.email, e.d_id,d.dept_id,d.dept_name
</sql>

（3）新建select查询（查询员工同时带部门信息）

    <!-- 查询员工同时带部门信息 -->
  <select id="selectByExampleWithDept" resultMap="WithDeptResultMap">
    select
    <if test="distinct">
      distinct
    </if>
    <include refid="WithDept_Base_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>
  <select id="selectByPrimaryKeyWithDept" resultMap="WithDeptResultMap">
    select 
    <include refid="WithDept_Base_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>