标签:dell 一对一 tor 命名 timestamp string main scons 下划线
这是mybatis系列第7篇。没看前文的建议先去【Java冢狐】公众号中查看前文,方便理解和掌握。上一篇中我们讲述了一些关于获取主键的方法,这篇文章中我们将会更加深入的介绍一些查询的方法,特别是多表查询。
在开始之前先开始诸如建库建表等准备工作。
创建一个db:mybatisdemo
4张表:
表之间的关系:
具体的建表语句如下所示:
DROP DATABASE IF EXISTS `mybatisdemo`;
CREATE DATABASE `mybatisdemo`;
USE `mybatisdemo`;
DROP TABLE IF EXISTS user;
CREATE TABLE user(
id int AUTO_INCREMENT PRIMARY KEY COMMENT ‘用户id‘,
name VARCHAR(32) NOT NULL DEFAULT ‘‘ COMMENT ‘用户名‘
) COMMENT ‘用户表‘;
INSERT INTO user VALUES (1,‘冢狐‘),(2,‘Java冢狐‘);
DROP TABLE IF EXISTS goods;
CREATE TABLE goods(
id int AUTO_INCREMENT PRIMARY KEY COMMENT ‘商品id‘,
name VARCHAR(32) NOT NULL DEFAULT ‘‘ COMMENT ‘商品名称‘,
price DECIMAL(10,2) NOT NULL DEFAULT 0 COMMENT ‘商品价格‘
) COMMENT ‘商品信息表‘;
INSERT INTO goods VALUES (1,‘Mybatis系列‘,8.00),(2,‘spring系列‘,16.00);
DROP TABLE IF EXISTS orders;
CREATE TABLE orders(
id int AUTO_INCREMENT PRIMARY KEY COMMENT ‘订单id‘,
user_id INT NOT NULL DEFAULT 0 COMMENT ‘用户id,来源于user.id‘,
create_time BIGINT NOT NULL DEFAULT 0 COMMENT ‘订单创建时间(时间戳,秒)‘,
up_time BIGINT NOT NULL DEFAULT 0 COMMENT ‘订单最后修改时间(时间戳,秒)‘
) COMMENT ‘订单表‘;
INSERT INTO orders VALUES (1,2,unix_timestamp(now()),unix_timestamp(now())),(2,1,unix_timestamp(now()),unix_timestamp(now()));
DROP TABLE IF EXISTS order_detail;
CREATE TABLE order_detail(
id int AUTO_INCREMENT PRIMARY KEY COMMENT ‘订单明细id‘,
order_id INT NOT NULL DEFAULT 0 COMMENT ‘订单id,来源于order.id‘,
goods_id INT NOT NULL DEFAULT 0 COMMENT ‘商品id,来源于goods.id‘,
num INT NOT NULL DEFAULT 0 COMMENT ‘商品数量‘,
total_price DECIMAL(12,2) NOT NULL DEFAULT 0 COMMENT ‘商品总金额‘
) COMMENT ‘订单表‘;
INSERT INTO order_detail VALUES (1,1,1,2,16.00),(2,1,1,1,16.00),(3,2,1,1,8.00);
select * from user;
select * from goods;
select * from orders;
select * from order_detail;
建好库和表后,下一步我们就开始我们的查询之旅,先从最基础的单表查询看起,依次介绍单表查询、一对一查询和一对多查询。
先来介绍的就是单表查询。
需要按照订单id查询订单信息。
db中表的字段是采用下划线分割的,model中我们是采用骆驼命名法来命名的,如OrderModel:
package com.zhonghu.chat07.demo1.model;
import lombok.*;
import java.util.List;
@Getter
@Setter
@Builder
@ToString
@NoArgsConstructor
@AllArgsConstructor
public class OrderModel {
private Integer id;
private Integer userId;
private Long createTime;
private Long upTime;
}
其他几个Model也类似。
<select id="getById" resultType="com.zhonghu.chat07.demo1.model.OrderModel">
<![CDATA[
SELECT a.id,a.user_id as userId,a.create_time createTime,a.up_time upTime FROM orders a WHERE a.id = #{value}
]]>
</select>
注意上面的resultType,标识结果的类型。
OrderModel getById(int id);
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- 引入外部jdbc配置 -->
<properties resource="jdbc.properties"/>
<!-- 环境配置,可以配置多个环境 -->
<environments default="demo4">
<environment id="demo4">
<!-- 事务管理器工厂配置 -->
<transactionManager type="JDBC"/>
<!-- 数据源工厂配置,使用工厂来创建数据源 -->
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="demo1/mapper/UserMapper.xml" />
<mapper resource="demo1/mapper/GoodsMapper.xml" />
<mapper resource="demo1/mapper/OrderMapper.xml" />
<mapper resource="demo1/mapper/OrderDetailMapper.xml" />
</mappers>
</configuration>
com.zhonghu.chat07.demo1.Demo1Test#getById
@Before
public void before() throws IOException {
//指定mybatis全局配置文件
String resource = "demo1/mybatis-config.xml";
//读取全局配置文件
InputStream inputStream = Resources.getResourceAsStream(resource);
//构建SqlSessionFactory对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
this.sqlSessionFactory = sqlSessionFactory;
}
@Test
public void getById() {
try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) {
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
OrderModel orderModel = mapper.getById(1);
log.info("{}", orderModel);
}
}
35:59.211 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById - ==> Preparing: SELECT a.id,a.user_id as userId,a.create_time createTime,a.up_time upTime FROM orders a WHERE a.id = ?
35:59.239 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById - ==> Parameters: 1(Integer)
35:59.258 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById - <== Total: 1
35:59.258 [main] INFO c.j.chat05.demo1.Demo1Test - OrderModel(id=1, userId=2, createTime=1610803573, upTime=1610803573)
sql中我们使用了别名,将orders中的字段转换成了和OrderModel中字段一样的名称,最后mybatis内部会通过反射,将查询结果按照名称到OrderModel中查找同名的字段,然后进行赋值。
若我们项目中表对应的Model中的字段都是采用骆驼命名法,mybatis中可以进行一些配置,可以使表中的字段和对应Model中骆驼命名法的字段进行自动映射。
需要在mybatis全局配置文件中加入下面配置:
<settings>
<!-- 是否开启自动驼峰命名规则映射,及从xx_yy映射到xxYy -->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<select id="getById1" resultType="com.zhonghu.chat07.demo1.model.OrderModel">
<![CDATA[
SELECT a.id,a.user_id,a.create_time,a.up_time FROM orders a WHERE a.id = #{value}
]]>
</select>
注意上面的sql,我们没有写别名了,由于我们开启了自动骆驼命名映射,所以查询结果会按照下面的关系进行自动映射:
sql对应的字段 | OrderModel中的字段 |
---|---|
id | id |
user_id | userId |
create_time | createTime |
up_time | upTime |
OrderModel getById1(int id);
com.zhonghu.chat05.demo1.Demo1Test#getById1
@Test
public void getById1() {
try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) {
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
OrderModel orderModel = mapper.getById1(1);
log.info("{}", orderModel);
}
}
59:44.884 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById1 - ==> Preparing: SELECT a.id,a.user_id,a.create_time,a.up_time FROM orders a WHERE a.id = ?
59:44.917 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById1 - ==> Parameters: 1(Integer)
59:44.935 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById1 - <== Total: 1
59:44.935 [main] INFO c.j.chat05.demo1.Demo1Test - OrderModel(id=1, userId=2, createTime=1610803573, upTime=1610803573)
输出中可以看出,sql中的字段是下划线的方式,OrderModel中的字段是骆驼命名法,结果也自动装配成功,这个就是开启mapUnderscoreToCamelCase产生的效果。
mapper xml中有个更强大的元素resultMap,通过这个元素可以定义查询结果的映射关系。
<resultMap id="orderModelMap2" type="com.zhonghu.chat07.demo1.model.OrderModel">
<id column="id" property="id" />
<result column="user_id" property="userId" />
<result column="create_time" property="createTime" />
<result column="up_time" property="upTime" />
</resultMap>
<select id="getById2" resultMap="orderModelMap2">
<![CDATA[
SELECT a.id,a.user_id,a.create_time,a.up_time FROM orders a WHERE a.id = #{value}
]]>
</select>
上面resultMap有2个元素需要指定:
注意上面的select元素,有个resultMap,标识查询结果使用哪个resultMap进行映射,此处我们使用的是orderModelMap2,所以查询结果会按照orderModelMap2关联的resultMap进行映射。
OrderModel getById2(int id);
com.zhonghu.chat07.demo1.Demo1Test#getById2
@Test
public void getById2() {
try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) {
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
OrderModel orderModel = mapper.getById2(1);
log.info("{}", orderModel);
}
}
运行输出
14:12.518 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById2 - ==> Preparing: SELECT a.id,a.user_id,a.create_time,a.up_time FROM orders a WHERE a.id = ?
14:12.546 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById2 - ==> Parameters: 1(Integer)
14:12.564 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById2 - <== Total: 1
14:12.564 [main] INFO c.j.chat05.demo1.Demo1Test - OrderModel(id=1, userId=2, createTime=1610803573, upTime=1610803573)
讲完了单表查询,下面开始连表查询,首先就是一对一的查询
通过订单id查询订单的时候,将订单关联的用户信息也返回。
我们修改一下OrderModel代码,内部添加一个UserModel,如下:
package com.zhonghu.chat07.demo2.model;
import lombok.*;
import java.util.List;
@Getter
@Setter
@Builder
@ToString
@NoArgsConstructor
@AllArgsConstructor
public class OrderModel {
private Integer id;
private Integer userId;
private Long createTime;
private Long upTime;
//下单用户信息
private UserModel userModel;
}
UserModel内容:
package com.zhonghu.chat07.demo2.model;
import lombok.*;
@Getter
@Setter
@Builder
@ToString
@NoArgsConstructor
@AllArgsConstructor
public class UserModel {
private Integer id;
private String name;
}
<resultMap id="orderModelMap1" type="com.zhonghu.chat07.demo2.model.OrderModel">
<id column="id" property="id" />
<result column="user_id" property="userId"/>
<result column="create_time" property="createTime"/>
<result column="up_time" property="upTime"/>
<result column="user_id" property="userModel.id"/>
<result column="name" property="userModel.name"/>
</resultMap>
<select id="getById1" resultMap="orderModelMap1">
<![CDATA[
SELECT
a.id,
a.user_id,
a.create_time,
a.up_time,
b.name
FROM
orders a,
user b
WHERE
a.user_id = b.id
AND a.id = #{value}
]]>
</select>
注意重点在于上面的这两行:
<result column="user_id" property="userModel.id"/>
<result column="name" property="userModel.name"/>
这个地方使用到了级联赋值,多级之间用.进行引用,此处我们只有一级,可以有很多级。
OrderModel getById1(int id);
com.zhonghu.chat07.demo2.Demo2Test#getById1
@Before
public void before() throws IOException {
//指定mybatis全局配置文件
String resource = "demo2/mybatis-config.xml";
//读取全局配置文件
InputStream inputStream = Resources.getResourceAsStream(resource);
//构建SqlSessionFactory对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
this.sqlSessionFactory = sqlSessionFactory;
}
@Test
public void getById1() {
try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) {
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
OrderModel orderModel = mapper.getById1(1);
log.info("{}", orderModel);
}
}
24:20.811 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById1 - ==> Preparing: SELECT a.id, a.user_id, a.create_time, a.up_time, b.name FROM orders a, user b WHERE a.user_id = b.id AND a.id = ?
24:20.843 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById1 - ==> Parameters: 1(Integer)
24:20.861 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById1 - <== Total: 1
24:20.861 [main] INFO c.j.chat05.demo2.Demo2Test - OrderModel(id=1, userId=2, createTime=1610803573, upTime=1610803573, userModel=UserModel(id=2, name=Java冢狐))
这次我们需要使用mapper xml中另外一个元素association,这个元素可以配置关联对象的映射关系,看示例。
<resultMap id="orderModelMap2" type="com.zhonghu.chat07.demo2.model.OrderModel">
<id column="id" property="id" />
<result column="user_id" property="userId"/>
<result column="create_time" property="createTime"/>
<result column="up_time" property="upTime"/>
<association property="userModel">
<id column="user_id" property="id"/>
<result column="name" property="name" />
</association>
</resultMap>
<select id="getById2" resultMap="orderModelMap2">
<![CDATA[
SELECT
a.id,
a.user_id,
a.create_time,
a.up_time,
b.name
FROM
orders a,
user b
WHERE
a.user_id = b.id
AND a.id = #{value}
]]>
</select>
注意上面下面这部分代码:
<association property="userModel">
<id column="user_id" property="id"/>
<result column="name" property="name" />
</association>
注意上面的property属性,这个就是配置sql查询结果和OrderModel.userModel对象的映射关系,将user_id和userModel中的id进行映射,name和userModel中的name进行映射。
OrderModel getById2(int id);
@Test
public void getById2() {
try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) {
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
OrderModel orderModel = mapper.getById2(1);
log.info("{}", orderModel);
}
}
51:44.896 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById2 - ==> Preparing: SELECT a.id, a.user_id, a.create_time, a.up_time, b.name FROM orders a, user b WHERE a.user_id = b.id AND a.id = ?
51:44.925 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById2 - ==> Parameters: 1(Integer)
51:44.941 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById2 - <== Total: 1
51:44.942 [main] INFO c.j.chat05.demo2.Demo2Test - OrderModel(id=1, userId=2, createTime=1610803573, upTime=1610803573, userModel=UserModel(id=2, name=Java冢狐))
从结果的最后一行可以看出,所有字段的值映射都是ok的。
先按照订单id查询订单数据,然后在通过订单中user_id去用户表查询用户数据,通过两次查询,组合成目标结果,mybatis已经内置了这种操作,如下。
我们先定义一个通过用户id查询用户信息的select元素,如下
<select id="getById" resultType="com.zhonghu.chat07.demo2.model.UserModel">
<![CDATA[
SELECT id,name FROM user where id = #{value}
]]>
</select>
<resultMap id="orderModelMap3" type="com.zhonghu.chat07.demo2.model.OrderModel">
<id column="id" property="id" />
<result column="user_id" property="userId"/>
<result column="create_time" property="createTime"/>
<result column="up_time" property="upTime"/>
<association property="userModel" select="com.zhonghu.chat07.demo2.mapper.UserMapper.getById" column="user_id" />
</resultMap>
<select id="getById3" resultMap="orderModelMap3">
<![CDATA[
SELECT
a.id,
a.user_id,
a.create_time,
a.up_time
FROM
orders a
WHERE
a.id = #{value}
]]>
</select>
OrderModel.userModel属性的值来在于另外一个查询,这个查询是通过association元素的select属性指定的,此处使用的是
com.zhonghu.chat07.demo2.mapper.UserMapper.getById
这个查询是有条件的,条件通过association的column进行传递的,此处传递的是getById3查询结果中的user_id字段。
OrderModel getById3(int id);
com.zhonghu.chat07.demo2.Demo2Test#getById3
@Test
public void getById3() {
try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) {
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
OrderModel orderModel = mapper.getById3(1);
log.info("{}", orderModel);
}
}
07:12.569 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById3 - ==> Preparing: SELECT a.id, a.user_id, a.create_time, a.up_time FROM orders a WHERE a.id = ?
07:12.600 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById3 - ==> Parameters: 1(Integer)
07:12.619 [main] DEBUG c.j.c.d.mapper.UserMapper.getById - ====> Preparing: SELECT id,name FROM user where id = ?
07:12.620 [main] DEBUG c.j.c.d.mapper.UserMapper.getById - ====> Parameters: 2(Integer)
07:12.625 [main] DEBUG c.j.c.d.mapper.UserMapper.getById - <==== Total: 1
07:12.625 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById3 - <== Total: 1
07:12.625 [main] INFO c.j.chat05.demo2.Demo2Test - OrderModel(id=1, userId=2, createTime=1610803573, upTime=1610803573, userModel=UserModel(id=2, name=Java冢狐))
从输出中可以看出有2次查询,先按照订单id查询订单,然后通过订单记录中用户id去用户表查询用户信息,最终执行了2次查询。
方式3中给第二个查询传递了一个参数,如果需要给第二个查询传递多个参数怎么办呢?可以这么写
<association property="属性" select="查询对应的select的id" column="{key1=父查询字段1,key2=父查询字段2,key3=父查询字段3}" />
这种相当于给子查询传递了一个map,子查询中 需要用过map的key获取对应的条件,看案例:
OrderMapper.xml
<resultMap id="orderModelMap4" type="com.zhonghu.chat07.demo2.model.OrderModel">
<id column="id" property="id" />
<result column="user_id" property="userId"/>
<result column="create_time" property="createTime"/>
<result column="up_time" property="upTime"/>
<association property="userModel" select="com.zhonghu.chat07.demo2.mapper.UserMapper.getById1" column="{uid1=user_id,uid2=create_time}" />
</resultMap>
<select id="getById4" resultMap="orderModelMap4">
<![CDATA[
SELECT
a.id,
a.user_id,
a.create_time,
a.up_time
FROM
orders a
WHERE
a.id = #{value}
]]>
</select>
UserMapper.xml
<select id="getById1" resultType="com.zhonghu.chat07.demo2.model.UserModel">
<![CDATA[
SELECT id,name FROM user where id = #{uid1} and id = #{uid2}
]]>
</select>
Mapper接口
OrderModel getById4(int id);
测试用例
com.zhonghu.chat07.demo2.Demo2Test#getById4
@Test
public void getById4() {
try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) {
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
OrderModel orderModel = mapper.getById4(1);
log.info("{}", orderModel);
}
}
运行输出
19:59.881 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById4 - ==> Preparing: SELECT a.id, a.user_id, a.create_time, a.up_time FROM orders a WHERE a.id = ?
19:59.914 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById4 - ==> Parameters: 1(Integer)
19:59.934 [main] DEBUG c.j.c.d.mapper.UserMapper.getById1 - ====> Preparing: SELECT id,name FROM user where id = ? and id = ?
19:59.934 [main] DEBUG c.j.c.d.mapper.UserMapper.getById1 - ====> Parameters: 2(Integer), 1610803573(Long)
19:59.939 [main] DEBUG c.j.c.d.mapper.UserMapper.getById1 - <==== Total: 0
19:59.939 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById4 - <== Total: 1
19:59.939 [main] INFO c.j.chat05.demo2.Demo2Test - OrderModel(id=1, userId=2, createTime=1610803573, upTime=1610803573, userModel=null)
输出中看一下第二个查询的条件,传过来的是第一个查询的user_id和create_time。
最后就是进行一队多查询的解析
根据订单id查询出订单信息,并且查询出订单明细列表。
先修改一下OrderModel代码,如下:
package com.zhonghu.chat07.demo3.model;
import lombok.*;
import java.util.List;
@Getter
@Setter
@Builder
@ToString
@NoArgsConstructor
@AllArgsConstructor
public class OrderModel {
private Integer id;
private Integer userId;
private Long createTime;
private Long upTime;
//订单详情列表
private List<OrderDetailModel> orderDetailModelList;
}
OrderModel中添加了一个集合orderDetailModelList用来存放订单详情列表。
<resultMap id="orderModelMap1" type="com.zhonghu.chat07.demo3.model.OrderModel">
<id column="id" property="id"/>
<result column="user_id" property="userId"/>
<result column="create_time" property="createTime"/>
<result column="up_time" property="upTime"/>
<collection property="orderDetailModelList" ofType="com.zhonghu.chat07.demo3.model.OrderDetailModel">
<id column="orderDetailId" property="id"/>
<result column="order_id" property="orderId"/>
<result column="goods_id" property="goodsId"/>
<result column="num" property="num"/>
<result column="total_price" property="totalPrice"/>
</collection>
</resultMap>
<select id="getById1" resultMap="orderModelMap1">
<![CDATA[
SELECT
a.id ,
a.user_id,
a.create_time,
a.up_time,
b.id orderDetailId,
b.order_id,
b.goods_id,
b.num,
b.total_price
FROM
orders a,
order_detail b
WHERE
a.id = b.order_id
AND a.id = #{value}
]]>
</select>
注意上面的getById1中的sql,这个sql中使用到了t_order和t_order_detail连接查询,这个查询会返回多条结果,但是最后结果按照orderModelMap1进行映射,最后只会返回一个OrderModel对象,关键在于collection元素,这个元素用来定义集合中元素的映射关系,有2个属性需要注意:
原理是这样的,注意orderModelMap1中有个
<id column="id" property="id"/>
查询出来的结果会按照这个配置中指定的column进行分组,即按照订单id进行分组,每个订单对应多个订单明细,订单明细会按照collection的配置映射为ofType元素指定的对象。
实际resultMap元素中的id元素可以使用result元素代替,只是用id可以提升性能,mybatis可以通过id元素配置的列的值判断唯一一条记录,如果我们使用result元素,那么判断是否是同一条记录的时候,需要通过所有列去判断了,所以通过id可以提升性能,使用id元素在一对多中可以提升性能,在单表查询中使用id元素还是result元素,性能都是一样的。
OrderModel getById1(Integer id);
com.zhonghu.chat07.demo3.Demo3Test#getById1
@Before
public void before() throws IOException {
//指定mybatis全局配置文件
String resource = "demo3/mybatis-config.xml";
//读取全局配置文件
InputStream inputStream = Resources.getResourceAsStream(resource);
//构建SqlSessionFactory对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
this.sqlSessionFactory = sqlSessionFactory;
}
@Test
public void getById1() {
try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) {
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
Integer id = 1;
OrderModel orderModel = mapper.getById1(id);
log.info("{}", orderModel);
}
}
03:52.092 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById1 - ==> Preparing: SELECT a.id , a.user_id, a.create_time, a.up_time, b.id orderDetailId, b.order_id, b.goods_id, b.num, b.total_price FROM orders a, order_detail b WHERE a.id = b.order_id AND a.id = ?
03:52.124 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById1 - ==> Parameters: 1(Integer)
03:52.148 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById1 - <== Total: 2
03:52.148 [main] INFO c.j.chat05.demo3.Demo3Test - OrderModel(id=1, userId=2, createTime=1610803573, upTime=1610803573, orderDetailModelList=[OrderDetailModel(id=1, orderId=1, goodsId=1, num=2, totalPrice=16.00), OrderDetailModel(id=2, orderId=1, goodsId=1, num=1, totalPrice=16.00)])
注意最后一条输出,和期望的结果一致。
通过2次查询,然后对结果进行分装,先通过订单id查询订单信息,然后通过订单id查询订单明细列表,然后封装结果。mybatis中默认支持这么玩,还是通过collection元素来实现的。
<select id="getListByOrderId1" resultType="com.zhonghu.chat07.demo3.model.OrderDetailModel" parameterType="int">
<![CDATA[
SELECT
a.id,
a.order_id AS orderId,
a.goods_id AS goodsId,
a.num,
a.total_price AS totalPrice
FROM
order_detail a
WHERE
a.order_id = #{value}
]]>
</select>
<resultMap id="orderModelMap2" type="com.zhonghu.chat07.demo3.model.OrderModel">
<id column="id" property="id"/>
<result column="user_id" property="userId"/>
<result column="create_time" property="createTime"/>
<result column="up_time" property="upTime"/>
<collection property="orderDetailModelList" select="com.zhonghu.chat07.demo3.mapper.OrderDetailMapper.getListByOrderId1" column="id"/>
</resultMap>
<select id="getById2" resultMap="orderModelMap2">
<![CDATA[
SELECT
a.id ,
a.user_id,
a.create_time,
a.up_time
FROM
orders a
WHERE
a.id = #{value}
]]>
</select>
重点在于下面这句配置:
<collection property="orderDetailModelList" select="com.zhonghu.chat07.demo3.mapper.OrderDetailMapper.getListByOrderId1" column="id"/>
表示orderDetailModelList属性的值通过select属性指定的查询获取,即:
com.zhonghu.chat07.demo3.mapper.OrderDetailMapper.getListByOrderId1
查询参数是通过column属性指定的,此处使用getById2 sql中的id作为条件,即订单id。
OrderModel getById2(int id);
com.zhonghu.chat07.demo3.Demo3Test#getById2
@Test
public void getById2() {
try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) {
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
OrderModel orderModel = mapper.getById2(1);
log.info("{}", orderModel);
}
}
10:07.087 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById2 - ==> Preparing: SELECT a.id , a.user_id, a.create_time, a.up_time FROM ordera a WHERE a.id = ?
10:07.117 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById2 - ==> Parameters: 1(Integer)
10:07.135 [main] DEBUG c.j.c.d.m.O.getListByOrderId1 - ====> Preparing: SELECT a.id, a.order_id AS orderId, a.goods_id AS goodsId, a.num, a.total_price AS totalPrice FROM order_detail a WHERE a.order_id = ?
10:07.136 [main] DEBUG c.j.c.d.m.O.getListByOrderId1 - ====> Parameters: 1(Integer)
10:07.141 [main] DEBUG c.j.c.d.m.O.getListByOrderId1 - <==== Total: 2
10:07.142 [main] DEBUG c.j.c.d.mapper.OrderMapper.getById2 - <== Total: 1
10:07.142 [main] INFO c.j.chat05.demo3.Demo3Test - OrderModel(id=1, userId=2, createTime=1610803573, upTime=1610803573, orderDetailModelList=[OrderDetailModel(id=1, orderId=1, goodsId=1, num=2, totalPrice=16.00), OrderDetailModel(id=2, orderId=1, goodsId=1, num=1, totalPrice=16.00)])
输出中有2次查询,先通过订单id查询订单信息,然后通过订单id查询订单明细,mybatis内部对结果进行了组装。
mybatis为我们提供了强大的关联查询,不过个人建议尽量少用,最好是采用单表的方式查询,在程序中通过多次查询,然后自己对结果进行组装。
Model中最好只定义一些和单表字段关联的属性,不要掺杂着其他对象的引用。
——我是冢狐,和你一样热爱编程。
欢迎关注公众号“Java冢狐”获取最新消息
标签:dell 一对一 tor 命名 timestamp string main scons 下划线
原文地址:https://www.cnblogs.com/javazhonghu/p/14408289.html