SSM框架的(CRUD)基础环境搭建4.0
2019-05-21 本文已影响0人
念念碎平安夜
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>