文章轉載自:http://www.itsoku.com/article/252
Mybatis系列目標:從入門開始開始掌握一個高級開發(fā)所需要的Mybatis技能。
這是mybatis系列第7篇英妓。
主要內容
單表查詢3種方式詳解
一對一關聯(lián)查詢(4種方式)詳解
一對多查詢(2種方式)詳解
綜合案例
總結
建議
建庫建表
創(chuàng)建一個db:javacode2018
丐膝,4張表:
- t_user(用戶表)
- t_goods(商品表)
- t_order(訂單表)
- t_order_detail(訂單明細表)
表之間的關系:
- t_order和t_user是一對一的關系,一條訂單關聯(lián)一個用戶記錄
- t_order和t_order_detail是一對多關系淫半,每個訂單中可能包含多個子訂單溃槐,每個子訂單對應一個商品
DROP DATABASE IF EXISTS `javacode2018`;
CREATE DATABASE `javacode2018`;
USE `javacode2018`;
DROP TABLE IF EXISTS t_user;
CREATE TABLE t_user(
id int AUTO_INCREMENT PRIMARY KEY COMMENT '用戶id',
name VARCHAR(32) NOT NULL DEFAULT '' COMMENT '用戶名'
) COMMENT '用戶表';
INSERT INTO t_user VALUES (1,'張學友'),(2,'路人甲Java');
DROP TABLE IF EXISTS t_goods;
CREATE TABLE t_goods(
id int AUTO_INCREMENT PRIMARY KEY COMMENT '商品id',
name VARCHAR(32) NOT NULL DEFAULT '' COMMENT '商品名稱',
price DECIMAL(10,2) NOT NULL DEFAULT 0 COMMENT '商品價格'
) COMMENT '商品信息表';
INSERT INTO t_goods VALUES (1,'Mybatis系列',8.88),(2,'maven高手系列',16.66);
DROP TABLE IF EXISTS t_order;
CREATE TABLE t_order(
id int AUTO_INCREMENT PRIMARY KEY COMMENT '訂單id',
user_id INT NOT NULL DEFAULT 0 COMMENT '用戶id,來源于t_user.id',
create_time BIGINT NOT NULL DEFAULT 0 COMMENT '訂單創(chuàng)建時間(時間戳科吭,秒)',
up_time BIGINT NOT NULL DEFAULT 0 COMMENT '訂單最后修改時間(時間戳昏滴,秒)'
) COMMENT '訂單表';
INSERT INTO t_order VALUES (1,2,unix_timestamp(now()),unix_timestamp(now())),(2,1,unix_timestamp(now()),unix_timestamp(now()));
DROP TABLE IF EXISTS t_order_detail;
CREATE TABLE t_order_detail(
id int AUTO_INCREMENT PRIMARY KEY COMMENT '訂單明細id',
order_id INT NOT NULL DEFAULT 0 COMMENT '訂單id猴鲫,來源于t_order.id',
goods_id INT NOT NULL DEFAULT 0 COMMENT '商品id,來源于t_goods.id',
num INT NOT NULL DEFAULT 0 COMMENT '商品數量',
total_price DECIMAL(12,2) NOT NULL DEFAULT 0 COMMENT '商品總金額'
) COMMENT '訂單表';
INSERT INTO t_order_detail VALUES (1,1,1,2,17.76),(2,1,1,1,16.66),(3,2,1,1,8.88);
select * from t_user;
select * from t_goods;
select * from t_order;
select * from t_order_detail;
單表查詢(3種方式)
需求
需要按照訂單id查詢訂單信息谣殊。
方式1
創(chuàng)建每個表對應的Model
db中表的字段是采用下劃線分割的拂共,model中我們是采用駱駝命名法來命名的,如OrderModel
:
package com.javacode2018.chat05.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;
}
其他幾個Model也類似姻几。
Mapper xml
<select id="getById" resultType="com.javacode2018.chat05.demo1.model.OrderModel">
<![CDATA[
SELECT a.id,a.user_id as userId,a.create_time createTime,a.up_time upTime FROM t_order a WHERE a.id = #{value}
]]>
</select>
注意上面的resultType
宜狐,標識結果的類型。
Mapper接口方法
OrderModel getById(int id);
mybatis全局配置文件
<?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"/>
<!-- 環(huán)境配置蛇捌,可以配置多個環(huán)境 -->
<environments default="demo4">
<environment id="demo4">
<!-- 事務管理器工廠配置 -->
<transactionManager type="JDBC"/>
<!-- 數據源工廠配置肌厨,使用工廠來創(chuàng)建數據源 -->
<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>
測試用例
com.javacode2018.chat05.demo1.Demo1Test#getById
@Before
public void before() throws IOException {
//指定mybatis全局配置文件
String resource = "demo1/mybatis-config.xml";
//讀取全局配置文件
InputStream inputStream = Resources.getResourceAsStream(resource);
//構建SqlSessionFactory對象
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);
}
}
運行輸出
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 t_order 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=1577947790, upTime=1577947790)
原理
sql中我們使用了別名,將t_order
中的字段轉換成了和OrderModel
中字段一樣的名稱豁陆,最后mybatis內部會通過反射柑爸,將查詢結果按照名稱到OrderModel
中查找同名的字段,然后進行賦值盒音。
方式2
若我們項目中表對應的Model中的字段都是采用駱駝命名法表鳍,mybatis中可以進行一些配置,可以使表中的字段和對應Model中駱駝命名法的字段進行自動映射祥诽。
需要在mybatis全局配置文件中加入下面配置:
<settings>
<!-- 是否開啟自動駝峰命名規(guī)則映射譬圣,及從xx_yy映射到xxYy -->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
Mapper xml
<select id="getById1" resultType="com.javacode2018.chat05.demo1.model.OrderModel">
<![CDATA[
SELECT a.id,a.user_id,a.create_time,a.up_time FROM t_order a WHERE a.id = #{value}
]]>
</select>
注意上面的sql,我們沒有寫別名了雄坪,由于我們開啟了自動駱駝命名映射厘熟,所以查詢結果會按照下面的關系進行自動映射:
sql對應的字段 | OrderModel中的字段 |
---|---|
id | id |
user_id | userId |
create_time | createTime |
up_time | upTime |
Mapper接口
OrderModel getById1(int id);
測試用例
com.javacode2018.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);
}
}
運行輸出
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 t_order 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=1577947790, upTime=1577947790)
輸出中可以看出,sql中的字段是下劃線的方式维哈,OrderModel中的字段是駱駝命名法绳姨,結果也自動裝配成功,這個就是開啟mapUnderscoreToCamelCase
產生的效果阔挠。
方式3
mapper xml中有個更強大的元素resultMap
飘庄,通過這個元素可以定義查詢結果的映射關系。
Mapper xml
<resultMap id="orderModelMap2" type="com.javacode2018.chat05.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 t_order a WHERE a.id = #{value}
]]>
</select>
上面resultMap
有2個元素需要指定:
- id:resultMap標識
- type:將結果封裝成什么類型购撼,此處我們需要將結果分裝為
OrderModel
注意上面的select元素跪削,有個resultMap
,標識查詢結果使用哪個resultMap
進行映射迂求,此處我們使用的是orderModelMap2
碾盐,所以查詢結果會按照orderModelMap2
關聯(lián)的resultMap
進行映射。
Mapper接口
OrderModel getById2(int id);
測試用例
com.javacode2018.chat05.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);
}
}
運行輸出
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 t_order 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=1577947790, upTime=1577947790)
一對一關聯(lián)查詢(4種方式)
需求
通過訂單id查詢訂單的時候揩局,將訂單關聯(lián)的用戶信息也返回毫玖。
我們修改一下OrderModel
代碼,內部添加一個UserModel
,如下:
package com.javacode2018.chat05.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;
//下單用戶信息
private UserModel userModel;
}
UserModel內容:
package com.javacode2018.chat05.demo2.model;
import lombok.*;
@Getter
@Setter
@Builder
@ToString
@NoArgsConstructor
@AllArgsConstructor
public class UserModel {
private Integer id;
private String name;
}
方式1
Mapper xml
<resultMap id="orderModelMap1" type="com.javacode2018.chat05.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
t_order a,
t_user b
WHERE
a.user_id = b.id
AND a.id = #{value}
]]>
</select>
注意重點在于上面的這兩行:
<result column="user_id" property="userModel.id"/>
<result column="name" property="userModel.name"/>
這個地方使用到了級聯(lián)賦值孕豹,多級之間用.
進行引用涩盾,此處我們只有一級励背,可以有很多級春霍。
Mapper 接口
OrderModel getById1(int id);
測試用例
com.javacode2018.chat05.demo2.Demo2Test#getById1
@Before
public void before() throws IOException {
//指定mybatis全局配置文件
String resource = "demo2/mybatis-config.xml";
//讀取全局配置文件
InputStream inputStream = Resources.getResourceAsStream(resource);
//構建SqlSessionFactory對象
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);
}
}
運行輸出
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 t_order a, t_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=1577947790, upTime=1577947790, userModel=UserModel(id=2, name=路人甲Java))
方式2
這次我們需要使用mapper xml中另外一個元素association
,這個元素可以配置關聯(lián)對象的映射關系叶眉,看示例址儒。
Mapper xml
<resultMap id="orderModelMap2" type="com.javacode2018.chat05.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
t_order a,
t_user b
WHERE
a.user_id = b.id
AND a.id = #{value}
]]>
</select>
注意上面下面這部分代碼:
<association property="userModel">
<id column="user_id" property="id"/>
<result column="name" property="name" />
</association>
注意上面的property
屬性,這個就是配置sql查詢結果和OrderModel.userModel
對象的映射關系衅疙,將user_id
和userModel中的id進行映射
,name和userModel中的name進行映射
莲趣。
Mapper接口
OrderModel getById2(int id);
測試用例
@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);
}
}
運行結果
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 t_order a, t_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=1577947790, upTime=1577947790, userModel=UserModel(id=2, name=路人甲Java))
從結果的最后一行可以看出,所有字段的值映射都是ok的饱溢。
方式3
先按照訂單id查詢訂單數據喧伞,然后在通過訂單中user_id
去用戶表查詢用戶數據,通過兩次查詢绩郎,組合成目標結果潘鲫,mybatis已經內置了這種操作,如下肋杖。
UserMapper.xml
我們先定義一個通過用戶id查詢用戶信息的select元素溉仑,如下
<select id="getById" resultType="com.javacode2018.chat05.demo2.model.UserModel">
<![CDATA[
SELECT id,name FROM t_user where id = #{value}
]]>
</select>
OrderModel.xml
<resultMap id="orderModelMap3" type="com.javacode2018.chat05.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.javacode2018.chat05.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
t_order a
WHERE
a.id = #{value}
]]>
</select>
OrderModel.userModel
屬性的值來在于另外一個查詢,這個查詢是通過association
元素的select
屬性指定的状植,此處使用的是
com.javacode2018.chat05.demo2.mapper.UserMapper.getById
這個查詢是有條件的浊竟,條件通過association
的column
進行傳遞的,此處傳遞的是getById3
查詢結果中的user_id
字段津畸。
Mapper接口
OrderModel getById3(int id);
測試用例
com.javacode2018.chat05.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);
}
}
運行輸出
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 t_order 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 t_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=1577947790, upTime=1577947790, userModel=UserModel(id=2, name=路人甲Java))
從輸出中可以看出有2次查詢丧肴,先按照訂單id查詢訂單,然后通過訂單記錄中用戶id去用戶表查詢用戶信息因宇,最終執(zhí)行了2次查詢。
方式4
方式3中給第二個查詢傳遞了一個參數,如果需要給第二個查詢傳遞多個參數怎么辦呢歹鱼?可以這么寫
<association property="屬性" select="查詢對應的select的id" column="{key1=父查詢字段1,key2=父查詢字段2,key3=父查詢字段3}" />
這種相當于給子查詢傳遞了一個map,子查詢中需要用過map的key獲取對應的條件区丑,看案例:
OrderMapper.xml
<resultMap id="orderModelMap4" type="com.javacode2018.chat05.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.javacode2018.chat05.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
t_order a
WHERE
a.id = #{value}
]]>
</select>
UserMapper.xml
<select id="getById1" resultType="com.javacode2018.chat05.demo2.model.UserModel">
<![CDATA[
SELECT id,name FROM t_user where id = #{uid1} and id = #{uid2}
]]>
</select>
Mapper接口
OrderModel getById4(int id);
測試用例
com.javacode2018.chat05.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);
}
}
運行輸出
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 t_order 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 t_user where id = ? and id = ?
19:59.934 [main] DEBUG c.j.c.d.mapper.UserMapper.getById1 - ====> Parameters: 2(Integer), 1577947790(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=1577947790, upTime=1577947790, userModel=null)
輸出中看一下第二個查詢的條件,傳過來的是第一個查詢的user_id和create_time
茫虽。
一對多查詢(2種方式)
需求
根據訂單id查詢出訂單信息刊苍,并且查詢出訂單明細列表。
先修改一下OrderModel代碼濒析,如下:
package com.javacode2018.chat05.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;
//訂單詳情列表
private List<OrderDetailModel> orderDetailModelList;
}
OrderModel中添加了一個集合orderDetailModelList
用來存放訂單詳情列表正什。
方式1
OrderMapper.xml
<resultMap id="orderModelMap1" type="com.javacode2018.chat05.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.javacode2018.chat05.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
t_order a,
t_order_detail b
WHERE
a.id = b.order_id
AND a.id = #{value}
]]>
</select>
注意上面的getById1
中的sql,這個sql中使用到了t_order和t_order_detail
連接查詢号杏,這個查詢會返回多條結果婴氮,但是最后結果按照orderModelMap1
進行映射,最后只會返回一個OrderModel
對象盾致,關鍵在于collection
元素主经,這個元素用來定義集合中元素的映射關系,有2個屬性需要注意:
- property:對應的屬性名稱
- ofType:集合中元素的類型庭惜,此處是
OrderDetailModel
原理是這樣的罩驻,注意orderModelMap1
中有個
<id column="id" property="id"/>
查詢出來的結果會按照這個配置中指定的column
進行分組,即按照訂單id
進行分組护赊,每個訂單對應多個訂單明細惠遏,訂單明細會按照collection
的配置映射為ofType元素指定的對象。
實際resultMap元素中的id元素可以使用result
元素代替骏啰,只是用id
可以提升性能节吮,mybatis可以通過id元素配置的列的值判斷唯一一條記錄,如果我們使用result
元素判耕,那么判斷是否是同一條記錄的時候透绩,需要通過所有列去判斷了,所以通過id
可以提升性能壁熄,使用id元素在一對多中可以提升性能帚豪,在單表查詢中使用id元素還是result元素,性能都是一樣的草丧。
Mapper接口
OrderModel getById1(Integer id);
測試用例
com.javacode2018.chat05.demo3.Demo3Test#getById1
@Before
public void before() throws IOException {
//指定mybatis全局配置文件
String resource = "demo3/mybatis-config.xml";
//讀取全局配置文件
InputStream inputStream = Resources.getResourceAsStream(resource);
//構建SqlSessionFactory對象
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);
}
}
運行輸出
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 t_order a, t_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=1577947790, upTime=1577947790, orderDetailModelList=[OrderDetailModel(id=1, orderId=1, goodsId=1, num=2, totalPrice=17.76), OrderDetailModel(id=2, orderId=1, goodsId=1, num=1, totalPrice=16.66)])
注意最后一條輸出志鞍,和期望的結果一致。
方式2
通過2次查詢方仿,然后對結果進行分裝,先通過訂單id查詢訂單信息,然后通過訂單id查詢訂單明細列表仙蚜,然后封裝結果此洲。mybatis中默認支持這么玩,還是通過collection
元素來實現的委粉。
OrderDetailMapper.xml
<select id="getListByOrderId1" resultType="com.javacode2018.chat05.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
t_order_detail a
WHERE
a.order_id = #{value}
]]>
</select>
OrderMapper.xml
<resultMap id="orderModelMap2" type="com.javacode2018.chat05.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.javacode2018.chat05.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
t_order a
WHERE
a.id = #{value}
]]>
</select>
重點在于下面這句配置:
<collection property="orderDetailModelList" select="com.javacode2018.chat05.demo3.mapper.OrderDetailMapper.getListByOrderId1" column="id"/>
表示orderDetailModelList
屬性的值通過select
屬性指定的查詢獲取呜师,即:
com.javacode2018.chat05.demo3.mapper.OrderDetailMapper.getListByOrderId1
查詢參數是通過column
屬性指定的,此處使用getById2
sql中的id
作為條件贾节,即訂單id汁汗。
Mapper接口
OrderModel getById2(int id);
測試用例
com.javacode2018.chat05.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);
}
}
運行輸出
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 t_order 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 t_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=1577947790, upTime=1577947790, orderDetailModelList=[OrderDetailModel(id=1, orderId=1, goodsId=1, num=2, totalPrice=17.76), OrderDetailModel(id=2, orderId=1, goodsId=1, num=1, totalPrice=16.66)])
輸出中有2次查詢,先通過訂單id查詢訂單信息栗涂,然后通過訂單id查詢訂單明細知牌,mybatis內部對結果進行了組裝。
綜合案例
入口
com.javacode2018.chat05.demo4.Demo4Test
這個案例中將上面多種查詢混合在一起了斤程,有興趣的可以去看看角寸,加深理解。
總結
- mybatis全局配置文件中通過
mapUnderscoreToCamelCase
可以開啟sql中的字段和javabean中的駱駝命名法的字段進行自動映射 - 掌握resultMap元素常見的用法
- 一對一關聯(lián)查詢使用
resultMap->association
元素(2種方式) - 一對多查詢使用
resultMap->collection
元素(2種方式) - resultMap中使用
id
元素主要在復雜的關聯(lián)查詢中可以提升效率忿墅,可以通過這個來判斷記錄的唯一性扁藕,如果沒有這個,需要通過所有的result相關的列才能判斷記錄的唯一性
建議
mybatis為我們提供了強大的關聯(lián)查詢疚脐,不過個人建議盡量少用亿柑,最好是采用單表的方式查詢,在程序中通過多次查詢棍弄,然后自己對結果進行組裝
望薄。
Model中最好只定義一些和單表字段關聯(lián)的屬性,不要摻雜著其他對象 的引用照卦。