mybatis详解四：一对一，一对多，多对多
一：创建UserMapper.xml 和 OrderMapper.xml文件
1：user表
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` varchar(11) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
`username` varchar(32) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '用户名称',
`birthday` timestamp NULL DEFAULT NULL COMMENT '生日',
`sex` int(8) NULL DEFAULT NULL COMMENT '性别 0:女 1：男',
`address` varchar(256) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '地址',
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact
INSERT INTO `user` VALUES ('1', 'lisi', '2019-01-26 21:23:30', 1, '遵义');
INSERT INTO `user` VALUES ('23', 'zhangsan', '2019-01-24 00:00:00', 2, '贵州');
SET FOREIGN_KEY_CHECKS = 1;
###### 2：order表
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
DROP TABLE IF EXISTS `order`;
CREATE TABLE `order` (
`order_id` varchar(100) CHARACTER SET latin1 COLLATE latin1_swedish_ci NOT NULL COMMENT '订单表主键',
`user_id` varchar(100) CHARACTER SET latin1 COLLATE latin1_swedish_ci NULL DEFAULT NULL,
`details` varchar(100) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
PRIMARY KEY (`order_id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = latin1 COLLATE = latin1_swedish_ci ROW_FORMAT = Compact;
INSERT INTO `order` VALUES ('1', '1', '电脑');
INSERT INTO `order` VALUES ('2', '1', '手机');
SET FOREIGN_KEY_CHECKS = 1;
1：OrderMapper.xml
<?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">
<!--namespace:值为对应的OrderMapper.java的全类名-->
<mapper namespace="mybatis1.mapper.OrderMapper">
<!-- 一对多查询 -->
<select id="getUserOrder" parameterType="String" resultMap="userOrder">
SELECT * FROM `user` u, `order` o
WHERE id = #{id} and u.id = o.user_id
</select>
<resultMap id="userOrder" type="User">
<!--主键id映射 有多个主键可以写多个此标签-->
<id property="id" column="id"/>
<!--property：对应java属性 column:对应表字段-->
<result property="username" column="username"/>
<result property="address" column="address"/>
<result property="birthday" column="birthday"/>
<!--ofType:返回的集合元素对应Order.java-->
<collection property="orderList" ofType="Order">
<id property="orderId" column="order_id"/>
<result property="userId" column="user_id"/>
<result property="details" column="details"/>
</collection>
</resultMap>
</mapper>
3 User.java
package mybatis1.pojo;
import java.sql.Timestamp;
import java.util.List;
/**
* Created by user on 2019/1/24.
*/
public class User {
private String id; //用户id
private String username;//用户姓名
private Timestamp birthday;//用户生日
private int sex;//用户性别
private String address;//用户地址
private List<Order> orderList;//用户订单列表
public User() {
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public Timestamp getBirthday() {
return birthday;
}
public void setBirthday(Timestamp birthday) {
this.birthday = birthday;
}
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public List<Order> getOrderList() {
return orderList;
}
public void setOrderList(List<Order> orderList) {
this.orderList = orderList;
}
}
4：Order.java
package mybatis1.pojo;
public class Order {
private String orderId;//订单id
private String details;//订单详情
private int price;//订单价格
private String id;//用户id
private User user;//一个订单只能属于一个用户
public Order() {
}
public String getOrderId() {
return orderId;
}
public void setOrderId(String orderId) {
this.orderId = orderId;
}
public String getDetails() {
return details;
}
public void setDetails(String details) {
this.details = details;
}
public int getPrice() {
return price;
}
public void setPrice(int price) {
this.price = price;
}
public String getUserId() {
return id;
}
public void setUserId(String id) {
this.id = id;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
}
二：创建userMapper.java和 OrderMapper.java文件
1.OrderMapper.java
package mybatis1.mapper;
import mybatis1.pojo.Order;
import mybatis1.pojo.User;
public interface OrderMapper {
//获取用户订单 一对一查询 第一种方式
public Order getOrderByOrderId1(Order order);
//获取用户订单 一对一查询 第二种方式
public Order getOrderByOrderId2(Order order);
//获取用户通过id
public User getUserById(String userId);
}
5:UserVo.java
package mybatis1.pojo;
import java.util.List;
public class UserVo {
private List<String> ids;
public List<String> getIds() {
return ids;
}
public void setIds(List<String> ids) {
this.ids = ids;
}
}
2.UserMapper.java文件
package mybatis1.mapper;
import mybatis1.pojo.User;
import mybatis1.pojo.UserVo;
import java.util.List;
public interface UserMapper {
//获取用户通过id
public User getUserById(String id);
//保存用户信息用户
public void saveUser(User user);
//更新用户信息
public void updateUser(User user);
//删除用户信息
public void deleteUserById(String id);
public User getUserByCondition(User user);
//获取用户信息通过条件
public User getUserByCondition1(User user);
//获取用户信息更加条件
public User getUserByCondition2(User user);
//获取多个用户
public List<User> getUsersByIds(UserVo userVo);
//获取用户的所有订单 一对多查询方式
public User getUserOrder(String userId);
}
三：创建测试用例
//一对一 第一种方式
@Test
public void getOrder(){
OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);
Order order = new Order();
order.setOrderId("1");
order.setUserId("1");
order = orderMapper.getOrderByOrderId1(order);
System.out.println(order);
}
//一对一 第er种方式
@Test
public void getOrder2(){
OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);
Order order = new Order();
order.setOrderId("2");
order = orderMapper.getOrderByOrderId2(order);
System.out.println(order);
}
//一对多查询
@Test
public void getUserOrder(){
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
User userOrder = userMapper.getUserOrder("1");
System.out.println(userOrder);
}
总结
1：至于mybatis的懒加载什么的就不写了，因为在项目中很少使用了。现在都是使用Redis替代了懒加载。
2：后期将写出Spring与mybatis的整合，在哪才会写mybatis事物相关的知识