不破楼兰终不还 !
不愿做咸鱼!
记住步骤(套路) :
- 明需求 -->2.表设计-->3.类设计-->4.Mapper接口和Mapper.xml文件-->5.编写单元测试 类
下面给大家演示一个例子 :
我们按上面地的步骤一步一步来 , 丝毫不慌 ! 十分简单 !
- 明需求
1.保存一个部门和两个员工，且这两个员工都是这个部门的。
2.根据员工 id 查询员工，并知道该员工的所在的部门。
-
表设计
image-20200530002519340.png
3.类设计( 根据需求和表设计 可以确定类应该如何设计 ! )
package cn.wolfcode.domain;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;
@Setter
@Getter
@ToString
public class Department {
private Long id;
private String name;
//部门表
}
package cn.wolfcode.domain;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;
@Setter
@Getter
@ToString
public class Employee {
private Long id;
private String name;
// 关联属性
private Department dept;
}
4.Mapper接口和Mapper.xml文件
package cn.wolfcode.mapper;
import cn.wolfcode.domain.Department;
public interface DepartmentMapper {
/**
* 保存操作
* @param dept
*/
void save(Department dept);
/**
* 查询 部门表
* @param id
* @return
*/
Department get(Long id);
}
<?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="cn.wolfcode.mapper.DepartmentMapper">
<!--
useGeneratedKeys=true 获取数据库保存数据的的主键值
keyProperty="id" 主键设置对象的 id 属性
-->
<!--保存的sql语句-->
<insert id="save" useGeneratedKeys="true" keyProperty="id">
INSERT INTO department(name) VALUES(#{name})
</insert>
<!--***************隔开看,一步步理解*********************-->
<!--查询操作 通过id 获取 id , name-->
<select id="get" resultType="Department">
SELECT id, name FROM department WHERE id = #{id}
</select>
</mapper>
package cn.wolfcode.mapper;
import cn.wolfcode.domain.Department;
import cn.wolfcode.domain.Employee;
import java.util.List;
public interface EmployeeMapper {
void save(Employee employee);
//查询单条数据 错误示范
Employee get(Long id);
//查询单条数据 正确示范
Employee get1(Long id);//使用方法 1
Employee get2(Long id);//使用方法 2 推荐 , 往下看
List<Employee> listAll();
}
<?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="cn.wolfcode.mapper.EmployeeMapper">
<!--
useGeneratedKeys=true 获取数据库保存数据的的主键值
keyProperty="id" 主键设置对象的 id 属性
-->
<!--保存的sql语句-->
<insert id="save" useGeneratedKeys="true" keyProperty="id">
INSERT INTO employee(name, deptId) VALUES(#{name}, #{dept.id})
</insert>
<!--查询的sql语句-->
<!--错误示范的 对应sql 这条查不出来的数据 deptId : null -->
<!--原因 : 数据对应不上 可以看看 Employee实体类的设计 一目了然-->
<select id="get" resultType="Employee">
SELECT id,name,deptId FROM employee WHERE id=#{id}
</select>
<!--所以上面这条查询的sql语句,不成立!-->
<!--方法1-->
<!--正确的查询语句-->
<resultMap id="baseResultMap1" type="Employee">
<!-- 什么列名对应值封装到对象的什么属性上 -->
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="deptId" property="dept.id"/>
</resultMap>
<!--正确示范的 对应sql-->
<select id="get1" resultMap="baseResultMap1">
SELECT id,name,deptId FROM employee WHERE id=#{id}
</select>
<!--方法2 推荐-->
<resultMap type="Employee" id="baseResultMap2">
<!-- 什么列名对应值封装到对象的什么属性上 -->
<id column="id" property="id"/>
<result column="name" property="name"/>
<!-- 使用额外 SQL
association 针对的关联属性配置，非集合类型
select 发送什么额外 SQL
column 发送额外 SQL 参数取上一条 SQL 哪个列的值
property 封装员工对象的什么属性 -->
<association select="cn.wolfcode.mapper.DepartmentMapper.get" column="deptId" property="dept"
javaType="Department"/>
</resultMap>
<select id="get2" resultMap="baseResultMap2">
SELECT id,name,deptId FROM employee WHERE id=#{id}
</select>
<select id="listAll" resultMap="baseResultMap2">
SELECT id, name, deptId FROM employee
</select>
</mapper>
5.编写单元测试
保存操作的测试 :
public class EmployeeMapperTest {
/**
* 保存操作
*
* @throws Exception
*/
@Test
public void testSave() throws Exception {
//创建部门类 对象 并设置值
Department department = new Department();
department.setName("财务部");
//创建员工类 对象 并设置值
Employee employee1 = new Employee();
Employee employee2 = new Employee();
employee1.setName("张无忌");
employee1.setDept(department);
employee2.setName("周芷诺");
employee2.setDept(department);
SqlSession session = MyBatisUtil.getSession();
//获取接口
EmployeeMapper employeeMapper = session.getMapper(EmployeeMapper.class);
//获取接口
DepartmentMapper departmentMapper = session.getMapper(DepartmentMapper.class);
//注意 先保存 部门表
//调用 departmentMapper 方法
departmentMapper.save(department);
//调用 employeeMapper 方法
employeeMapper.save(employee1);
employeeMapper.save(employee2);
//开启事务
session.commit();
//关闭资源
session.close();
}
}
查询操作的测试 :
public class Many2OneTest {
/**
* 错误 查询sql 的测试
* 结果 : DEBUG [main] - ==> Preparing: SELECT id,name,deptId FROM employee WHERE id=?
* Employee(id=1, name=张无忌, dept=null)
* @throws Exception
*/
@Test
public void testGet() throws Exception {
SqlSession session = MyBatisUtil.getSession();
EmployeeMapper employeeMapper = session.getMapper(EmployeeMapper.class);
Employee employee = employeeMapper.get(1L);
System.out.println(employee);
session.commit();
session.close();
}
/**
* 正确 查询sql 的测试
* 结果 :DEBUG [main] - ==> Preparing: SELECT id, name FROM department WHERE id = ?
* Employee(id=1, name=张无忌, dept=Department(id=1, name=财务部))
* @throws Exception
*/
@Test
public void testGet1() throws Exception {
SqlSession session = MyBatisUtil.getSession();
// 获取员工接口
EmployeeMapper employeeMapper = session.getMapper(EmployeeMapper.class);
//通过接口执行方法 获取 员工类对象
Employee employee = employeeMapper.get1(1L);
//因为 员工对象获取到了 并且得到 dept.id , 所以 通过
Long id = employee.getDept().getId();
DepartmentMapper departmentMapper = session.getMapper(DepartmentMapper.class);
Department department = departmentMapper.get(id);
employee.setDept(department);
//打印 员工对象
System.out.println(employee);
//执行事务
//关闭资源
session.commit();
session.close();
}
@Test
public void testGet2() throws Exception {
SqlSession session = MyBatisUtil.getSession();
EmployeeMapper employeeMapper = session.getMapper(EmployeeMapper.class);
Employee employee = employeeMapper.get2(1L);
System.out.println(employee);
session.commit();
session.close();
}
@Test
public void testListAll(){
SqlSession session = MyBatisUtil.getSession();
EmployeeMapper employeeMapper = session.getMapper(EmployeeMapper.class);
List<Employee> employees = employeeMapper.listAll();
System.out.println(employees);
session.close();
}
}
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