MyBatis与其使用方法讲解

ORM

在讲解Mybatis之前,我们需了解一个概念ORM(Object-Relational Mapping)对象关系映射,其是数据库与Java对象进行映射的一个技术.通过使用ORM,我们可以不用编写负责的Sql语句,而是通过操作对象来实现增删改查操作

缺优分析

• 优点
  
  
  
  • 提高开发效率,减少代码的重复性和维护成本
    
  • 增加代码的可读性,降低复杂度
    
  • 对数据库查询的细节进行抽象,隐藏了sql语句
    
  
  
• 缺点
  
  
  
  • 在进行多表联查时,或存在where条件时,ORM语句会变得复杂
    
  
  

MyBatis

• mybatis是一个支持自定义SQL的持久层框架,通过XML文件来实现SQL配置和数据映射,MyBatis允许开发者手动编写SQL语句,提高灵活性
  

Mybatis通过mapper文件,将sql查询和Java对象绑定到一起,简化了JDBC代码的编写,手动设置参数,获取结果集的工作

MyBatis的工作流程

• 其分为以下几步
  

MyBatis的基本使用

环境准备

• 引入依赖包:
  

1. <dependency>
2. <?xml version="1.0" encoding="UTF-8"?>
3. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
5. <mapper namespace="com.example.mapper.UserMapper">
6.    
7. </mapper><groupId>mysql</groupId>
8. <?xml version="1.0" encoding="UTF-8"?>
9. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
10.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
11. <mapper namespace="com.example.mapper.UserMapper">
12.    
13. </mapper>mysql-connector-java</artifactId>
14. <?xml version="1.0" encoding="UTF-8"?>
15. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
16.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
17. <mapper namespace="com.example.mapper.UserMapper">
18.    
19. </mapper><version>8.0.23</version>
20. </dependency>

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• 创建mybatis配置文件(mybatis-config.xml)
  

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
3. <configuration>
4. <?xml version="1.0" encoding="UTF-8"?>
5. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
6.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
7. <mapper namespace="com.example.mapper.UserMapper">
8.    
9. </mapper>
10. <?xml version="1.0" encoding="UTF-8"?>
11. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
12.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
13. <mapper namespace="com.example.mapper.UserMapper">
14.    
15. </mapper><environments default="mysql">
16. <?xml version="1.0" encoding="UTF-8"?>
17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
19. <mapper namespace="com.example.mapper.UserMapper">
20.    
21. </mapper><?xml version="1.0" encoding="UTF-8"?>
22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
24. <mapper namespace="com.example.mapper.UserMapper">
25.    
26. </mapper><environment id="mysql">
27. <?xml version="1.0" encoding="UTF-8"?>
28. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
29.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
30. <mapper namespace="com.example.mapper.UserMapper">
31.    
32. </mapper><?xml version="1.0" encoding="UTF-8"?>
33. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
34.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
35. <mapper namespace="com.example.mapper.UserMapper">
36.    
37. </mapper><?xml version="1.0" encoding="UTF-8"?>
38. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
39.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
40. <mapper namespace="com.example.mapper.UserMapper">
41.    
42. </mapper>
43. <?xml version="1.0" encoding="UTF-8"?>
44. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
45.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
46. <mapper namespace="com.example.mapper.UserMapper">
47.    
48. </mapper><?xml version="1.0" encoding="UTF-8"?>
49. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
50.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
51. <mapper namespace="com.example.mapper.UserMapper">
52.    
53. </mapper><?xml version="1.0" encoding="UTF-8"?>
54. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
55.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
56. <mapper namespace="com.example.mapper.UserMapper">
57.    
58. </mapper><transactionManager type="JDBC"></transactionManager>
59. <?xml version="1.0" encoding="UTF-8"?>
60. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
61.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
62. <mapper namespace="com.example.mapper.UserMapper">
63.    
64. </mapper><?xml version="1.0" encoding="UTF-8"?>
65. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
66.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
67. <mapper namespace="com.example.mapper.UserMapper">
68.    
69. </mapper><?xml version="1.0" encoding="UTF-8"?>
70. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
71.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
72. <mapper namespace="com.example.mapper.UserMapper">
73.    
74. </mapper>
75. <?xml version="1.0" encoding="UTF-8"?>
76. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
77.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
78. <mapper namespace="com.example.mapper.UserMapper">
79.    
80. </mapper><?xml version="1.0" encoding="UTF-8"?>
81. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
82.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
83. <mapper namespace="com.example.mapper.UserMapper">
84.    
85. </mapper><?xml version="1.0" encoding="UTF-8"?>
86. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
87.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
88. <mapper namespace="com.example.mapper.UserMapper">
89.    
90. </mapper><dataSource type="POOLED">
91. <?xml version="1.0" encoding="UTF-8"?>
92. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
93.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
94. <mapper namespace="com.example.mapper.UserMapper">
95.    
96. </mapper><?xml version="1.0" encoding="UTF-8"?>
97. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
98.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
99. <mapper namespace="com.example.mapper.UserMapper">
100.    
101. </mapper><?xml version="1.0" encoding="UTF-8"?>
102. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
103.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
104. <mapper namespace="com.example.mapper.UserMapper">
105.    
106. </mapper><?xml version="1.0" encoding="UTF-8"?>
107. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
108.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
109. <mapper namespace="com.example.mapper.UserMapper">
110.    
111. </mapper><property name="driver" value="com.mysql.cj.jdbc.Driver"/>
112. <?xml version="1.0" encoding="UTF-8"?>
113. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
114.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
115. <mapper namespace="com.example.mapper.UserMapper">
116.    
117. </mapper><?xml version="1.0" encoding="UTF-8"?>
118. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
119.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
120. <mapper namespace="com.example.mapper.UserMapper">
121.    
122. </mapper><?xml version="1.0" encoding="UTF-8"?>
123. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
124.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
125. <mapper namespace="com.example.mapper.UserMapper">
126.    
127. </mapper><?xml version="1.0" encoding="UTF-8"?>
128. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
129.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
130. <mapper namespace="com.example.mapper.UserMapper">
131.    
132. </mapper><property name="url" value="jdbc:mysql://localhost:3306/数据库名称?userSSL=false&serverTimezone=Asia/Shanghai"/>
133. <?xml version="1.0" encoding="UTF-8"?>
134. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
135.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
136. <mapper namespace="com.example.mapper.UserMapper">
137.    
138. </mapper><?xml version="1.0" encoding="UTF-8"?>
139. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
140.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
141. <mapper namespace="com.example.mapper.UserMapper">
142.    
143. </mapper><?xml version="1.0" encoding="UTF-8"?>
144. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
145.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
146. <mapper namespace="com.example.mapper.UserMapper">
147.    
148. </mapper><?xml version="1.0" encoding="UTF-8"?>
149. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
150.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
151. <mapper namespace="com.example.mapper.UserMapper">
152.    
153. </mapper><property name="username" value="帐号"/>
154. <?xml version="1.0" encoding="UTF-8"?>
155. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
156.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
157. <mapper namespace="com.example.mapper.UserMapper">
158.    
159. </mapper><?xml version="1.0" encoding="UTF-8"?>
160. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
161.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
162. <mapper namespace="com.example.mapper.UserMapper">
163.    
164. </mapper><?xml version="1.0" encoding="UTF-8"?>
165. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
166.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
167. <mapper namespace="com.example.mapper.UserMapper">
168.    
169. </mapper><?xml version="1.0" encoding="UTF-8"?>
170. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
171.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
172. <mapper namespace="com.example.mapper.UserMapper">
173.    
174. </mapper><property name="password" value="密码"/>
175. <?xml version="1.0" encoding="UTF-8"?>
176. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
177.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
178. <mapper namespace="com.example.mapper.UserMapper">
179.    
180. </mapper><?xml version="1.0" encoding="UTF-8"?>
181. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
182.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
183. <mapper namespace="com.example.mapper.UserMapper">
184.    
185. </mapper><?xml version="1.0" encoding="UTF-8"?>
186. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
187.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
188. <mapper namespace="com.example.mapper.UserMapper">
189.    
190. </mapper></dataSource>
191. <?xml version="1.0" encoding="UTF-8"?>
192. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
193.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
194. <mapper namespace="com.example.mapper.UserMapper">
195.    
196. </mapper><?xml version="1.0" encoding="UTF-8"?>
197. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
198.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
199. <mapper namespace="com.example.mapper.UserMapper">
200.    
201. </mapper></environment>
202. <?xml version="1.0" encoding="UTF-8"?>
203. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
204.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
205. <mapper namespace="com.example.mapper.UserMapper">
206.    
207. </mapper></environments>
208. <?xml version="1.0" encoding="UTF-8"?>
209. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
210.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
211. <mapper namespace="com.example.mapper.UserMapper">
212.    
213. </mapper>
214. <?xml version="1.0" encoding="UTF-8"?>
215. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
216.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
217. <mapper namespace="com.example.mapper.UserMapper">
218.    
219. </mapper>
220. <?xml version="1.0" encoding="UTF-8"?>
221. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
222.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
223. <mapper namespace="com.example.mapper.UserMapper">
224.    
225. </mapper><mappers>
226. <?xml version="1.0" encoding="UTF-8"?>
227. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
228.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
229. <mapper namespace="com.example.mapper.UserMapper">
230.    
231. </mapper><?xml version="1.0" encoding="UTF-8"?>
232. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
233.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
234. <mapper namespace="com.example.mapper.UserMapper">
235.    
236. </mapper><mapper resource="映射配置文件全路径"></mapper>
237. <?xml version="1.0" encoding="UTF-8"?>
238. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
239.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
240. <mapper namespace="com.example.mapper.UserMapper">
241.    
242. </mapper></mappers>
243. </configuration>

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• springboot中的application.yml
  

1. mybatis:
2.   # mapper配置文件
3.   mapper-locations: classpath:mapper/*.xml
4.   # resultType别名，没有这个配置resultType包名要写全，配置后只要写类名
5.   type-aliases-package: com.mashang.xiaomistore.domain
6.   configuration:
7. <?xml version="1.0" encoding="UTF-8"?>
8. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
9.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
10. <mapper namespace="com.example.mapper.UserMapper">
11.    
12. </mapper>#下划线自动转驼峰
13. <?xml version="1.0" encoding="UTF-8"?>
14. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
15.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
16. <mapper namespace="com.example.mapper.UserMapper">
17.    
18. </mapper>map-underscore-to-camel-case: true

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• 创建Mapper映射文件
  

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
3. <mapper namespace="com.company.mapper.StudentMapper">
4. <?xml version="1.0" encoding="UTF-8"?>
5. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
6.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
7. <mapper namespace="com.example.mapper.UserMapper">
8.    
9. </mapper><select id="queryAll" resultType="com.company.entity.Student">
10. <?xml version="1.0" encoding="UTF-8"?>
11. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
12.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
13. <mapper namespace="com.example.mapper.UserMapper">
14.    
15. </mapper><?xml version="1.0" encoding="UTF-8"?>
16. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
17.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
18. <mapper namespace="com.example.mapper.UserMapper">
19.    
20. </mapper>SELECT * FROM student
21. <?xml version="1.0" encoding="UTF-8"?>
22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
24. <mapper namespace="com.example.mapper.UserMapper">
25.    
26. </mapper></select>
27. </mapper>

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• 创建Mapper接口:
  

1. public interface StudentMapper {
2. <?xml version="1.0" encoding="UTF-8"?>
3. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
5. <mapper namespace="com.example.mapper.UserMapper">
6.    
7. </mapper>List<Student> queryAll();
8. }

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MyBatis日志配置

• 引入SpringBoot中的log4j
  

1. <dependency>
2. <?xml version="1.0" encoding="UTF-8"?>
3. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
5. <mapper namespace="com.example.mapper.UserMapper">
6.    
7. </mapper><groupId>org.springframework.boot</groupId>
8. <?xml version="1.0" encoding="UTF-8"?>
9. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
10.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
11. <mapper namespace="com.example.mapper.UserMapper">
12.    
13. </mapper>spring-boot-starter-log4j2</artifactId>
14. <?xml version="1.0" encoding="UTF-8"?>
15. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
16.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
17. <mapper namespace="com.example.mapper.UserMapper">
18.    
19. </mapper><version>3.4.3</version>
20. </dependency>

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• 在SpringBoot中在application.yml中mybatis配置项中进行配置
  

1. mybatis:
2.   configuration:
3. <?xml version="1.0" encoding="UTF-8"?>
4. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
5.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
6. <mapper namespace="com.example.mapper.UserMapper">
7.    
8. </mapper>log-impl: org.apache.ibatis.logging.log4j.Log4jImpl

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• 配置log4j.properties文件
  

1. ### 设置###
2. log4j.rootLogger = debug,stdout,D,E
4. ### 输出信息到控制抬 ###
5. log4j.appender.stdout = org.apache.log4j.ConsoleAppender
6. log4j.appender.stdout.Target = System.out
7. log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
8. log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n
10. ### 输出DEBUG 级别以上的日志到=D://logs/error.log ###
11. log4j.appender.D = org.apache.log4j.DailyRollingFileAppender
12. log4j.appender.D.File = D://logs/log.log
13. log4j.appender.D.Append = true
14. log4j.appender.D.Threshold = DEBUG
15. log4j.appender.D.layout = org.apache.log4j.PatternLayout
16. log4j.appender.D.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n
18. ### 输出ERROR 级别以上的日志到=D://logs/error.log ###
19. log4j.appender.E = org.apache.log4j.DailyRollingFileAppender
20. log4j.appender.E.File =D://logs/error.log
21. log4j.appender.E.Append = true
22. log4j.appender.E.Threshold = ERROR
23. log4j.appender.E.layout = org.apache.log4j.PatternLayout
24. log4j.appender.E.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

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• 一个基本的mybatis的XML模板如下
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>

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CURD实现

select查询

• 使用标签实现基本查询
  1. <select id ="getUserById" resultType="com.company.domain.entity.User">
  2.                 SELECT * FORM user
  3. </select>

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  • id:对应Mapper接口中的方法名,必须一致
    
  • resultType:指定返回结果映射到哪个Java类
    
  
  
• 传参#{}与${}的区别
  
  
  
  • #{}的特点
    
    
    
    • 事先进行预编译:使用#{}的参数会被Mybatis当作JDBC中的?占位符
      
    • 防止sql注入:由于会事先进行预编译,Mybatis能够防止Sql注入
      
    • 类型转换:会根据参数类型进行适当的类型转换
      
    
    
  • ${}的特点
    
    
    
    • 字符串拼接:&{}直接将字符串进行替换,相当于在Sql中直接拼接传入的参数
      
    • 存在sql注入的风险:没有预编译,会引发sql注入问题
      
    
    
  
  
• 多条件查询
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>SELECT * FROM user<?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper> WHERE name = #{name} AND age = #{age}

  复制代码
• 模糊查询
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper><?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper>SELECT *<?xml version="1.0" encoding="UTF-8"?>
  12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  14. <mapper namespace="com.example.mapper.UserMapper">
  15.    
  16. </mapper><?xml version="1.0" encoding="UTF-8"?>
  17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  19. <mapper namespace="com.example.mapper.UserMapper">
  20.    
  21. </mapper>FROM user<?xml version="1.0" encoding="UTF-8"?>
  22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  24. <mapper namespace="com.example.mapper.UserMapper">
  25.    
  26. </mapper><?xml version="1.0" encoding="UTF-8"?>
  27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  29. <mapper namespace="com.example.mapper.UserMapper">
  30.    
  31. </mapper>WHERE name LIKE CONCAT('%', #{name}, '%')

  复制代码
  
  
  • 使用LIKE关键字和CONCAT()函数进行查询
    
  
  

insert插入

• 使用标签实现基本插入操作
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper><?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper><?xml version="1.0" encoding="UTF-8"?>
  12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  14. <mapper namespace="com.example.mapper.UserMapper">
  15.    
  16. </mapper>INSERT INTO user(name, age)<?xml version="1.0" encoding="UTF-8"?>
  17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  19. <mapper namespace="com.example.mapper.UserMapper">
  20.    
  21. </mapper><?xml version="1.0" encoding="UTF-8"?>
  22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  24. <mapper namespace="com.example.mapper.UserMapper">
  25.    
  26. </mapper>VALUES (#{name}, #{age})<?xml version="1.0" encoding="UTF-8"?>
  27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  29. <mapper namespace="com.example.mapper.UserMapper">
  30.    
  31. </mapper>

  复制代码
  
  
  • parameterType:表示入参类型
    
  
  
• 实现回填自增主键
  
  
  
  • 使用userGeneratedKeys和keyProperty实现
    
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>INSERT INTO user (name, age)<?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper> VALUES (#{name}, #{age})

  复制代码
  
  
  • userGeneratedKeys:表示是否启动自增
    
  • keyProperty:表示将生成的主键赋值给哪个java对象的哪个属性如user.id
    
  
  

update更新

• 使用标签实现基本更新
  1.         <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper><?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper> UPDATE user<?xml version="1.0" encoding="UTF-8"?>
  12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  14. <mapper namespace="com.example.mapper.UserMapper">
  15.    
  16. </mapper><?xml version="1.0" encoding="UTF-8"?>
  17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  19. <mapper namespace="com.example.mapper.UserMapper">
  20.    
  21. </mapper>SET name=#{name},<?xml version="1.0" encoding="UTF-8"?>
  22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  24. <mapper namespace="com.example.mapper.UserMapper">
  25.    
  26. </mapper><?xml version="1.0" encoding="UTF-8"?>
  27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  29. <mapper namespace="com.example.mapper.UserMapper">
  30.    
  31. </mapper><?xml version="1.0" encoding="UTF-8"?>
  32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  34. <mapper namespace="com.example.mapper.UserMapper">
  35.    
  36. </mapper>age =#{age}<?xml version="1.0" encoding="UTF-8"?>
  37. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  38.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  39. <mapper namespace="com.example.mapper.UserMapper">
  40.    
  41. </mapper><?xml version="1.0" encoding="UTF-8"?>
  42. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  43.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  44. <mapper namespace="com.example.mapper.UserMapper">
  45.    
  46. </mapper>WHERE id = #{id}<?xml version="1.0" encoding="UTF-8"?>
  47. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  48.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  49. <mapper namespace="com.example.mapper.UserMapper">
  50.    
  51. </mapper>

  复制代码

delete删除

• 使用标签基本查询
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper><?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper><?xml version="1.0" encoding="UTF-8"?>
  12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  14. <mapper namespace="com.example.mapper.UserMapper">
  15.    
  16. </mapper>DELETE<?xml version="1.0" encoding="UTF-8"?>
  17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  19. <mapper namespace="com.example.mapper.UserMapper">
  20.    
  21. </mapper><?xml version="1.0" encoding="UTF-8"?>
  22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  24. <mapper namespace="com.example.mapper.UserMapper">
  25.    
  26. </mapper>FROM user<?xml version="1.0" encoding="UTF-8"?>
  27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  29. <mapper namespace="com.example.mapper.UserMapper">
  30.    
  31. </mapper><?xml version="1.0" encoding="UTF-8"?>
  32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  34. <mapper namespace="com.example.mapper.UserMapper">
  35.    
  36. </mapper>WHERE id = #{id}<?xml version="1.0" encoding="UTF-8"?>
  37. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  38.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  39. <mapper namespace="com.example.mapper.UserMapper">
  40.    
  41. </mapper>

  复制代码

传参方式

• 多参数传参(使用@Param)
  
  
  
  • 当方法有多个参数时,使用@Param注解明确参数名
    
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>SELECT * FROM user<?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper> WHERE name = #{name} AND age = #{age}

  复制代码
  
  
  • Mapper接口
    
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>User getUserByNameAndAge(<?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper><?xml version="1.0" encoding="UTF-8"?>
  12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  14. <mapper namespace="com.example.mapper.UserMapper">
  15.    
  16. </mapper><?xml version="1.0" encoding="UTF-8"?>
  17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  19. <mapper namespace="com.example.mapper.UserMapper">
  20.    
  21. </mapper>@Param("name") String name,<?xml version="1.0" encoding="UTF-8"?>
  22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  24. <mapper namespace="com.example.mapper.UserMapper">
  25.    
  26. </mapper><?xml version="1.0" encoding="UTF-8"?>
  27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  29. <mapper namespace="com.example.mapper.UserMapper">
  30.    
  31. </mapper><?xml version="1.0" encoding="UTF-8"?>
  32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  34. <mapper namespace="com.example.mapper.UserMapper">
  35.    
  36. </mapper>@Param("age") Integer age);

  复制代码
• 对象参数
  
  
  
  • 当参数为一个Java对象时,MyBatis自动将对象属性映射到Sql语句中的占位符
    
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>INSERT INTO user (name, age)<?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper> VALUES (#{name}, #{age})

  复制代码
  
  
  • #{name}对应user.name,#{age}对应user.age
    
  • Mapper接口
    
  1. void insertUser(User user);

  复制代码
• Map参数
  
  
  
  • 通过Map传递多个参数或动态参数
    
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>SELECT * FROM user<?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper> WHERE name = #{name} AND age = #{age}

  复制代码
  
  
  • Mapper接口
    
  1. User getUserByMap(Map<String, Object> params);

  复制代码
• 集合/数组参数
  
  
  
  • 适用于批量查询,比如WHERE id IN (…)
    
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>SELECT * FROM user<?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper> WHERE id IN<?xml version="1.0" encoding="UTF-8"?>
  12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  14. <mapper namespace="com.example.mapper.UserMapper">
  15.    
  16. </mapper><?xml version="1.0" encoding="UTF-8"?>
  17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  19. <mapper namespace="com.example.mapper.UserMapper">
  20.    
  21. </mapper><?xml version="1.0" encoding="UTF-8"?>
  22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  24. <mapper namespace="com.example.mapper.UserMapper">
  25.    
  26. </mapper>#{id}<?xml version="1.0" encoding="UTF-8"?>
  27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  29. <mapper namespace="com.example.mapper.UserMapper">
  30.    
  31. </mapper>

  复制代码
  
  
  • 是动态sql中的知识点等下会系统讲解
    
  • Mapper接口
    
  1. List<User> getUsersByIds(@Param("ids") List<Integer> ids);

  复制代码

动态sql

与标签

• :生成WHERE子句,并自动判断去掉开头多余的AND/OR关键字,使sql更简洁
  
• :用于判断传参条件,根据条件决定是否拼接某段SQL语句,适用于传参条件不固定,只有在满足条件时接入某个子串
  

1. <?xml version="1.0" encoding="UTF-8"?>
2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
4. <mapper namespace="com.example.mapper.UserMapper">
5.    
6. </mapper>SELECT * FROM user<?xml version="1.0" encoding="UTF-8"?>
7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
9. <mapper namespace="com.example.mapper.UserMapper">
10.    
11. </mapper><?xml version="1.0" encoding="UTF-8"?>
12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
14. <mapper namespace="com.example.mapper.UserMapper">
15.    
16. </mapper><?xml version="1.0" encoding="UTF-8"?>
17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
19. <mapper namespace="com.example.mapper.UserMapper">
20.    
21. </mapper><?xml version="1.0" encoding="UTF-8"?>
22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
24. <mapper namespace="com.example.mapper.UserMapper">
25.    
26. </mapper><?xml version="1.0" encoding="UTF-8"?>
27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
29. <mapper namespace="com.example.mapper.UserMapper">
30.    
31. </mapper><?xml version="1.0" encoding="UTF-8"?>
32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
34. <mapper namespace="com.example.mapper.UserMapper">
35.    
36. </mapper>AND name LIKE CONCAT('%', #{name}, '%')<?xml version="1.0" encoding="UTF-8"?>
37. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
38.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
39. <mapper namespace="com.example.mapper.UserMapper">
40.    
41. </mapper><?xml version="1.0" encoding="UTF-8"?>
42. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
43.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
44. <mapper namespace="com.example.mapper.UserMapper">
45.    
46. </mapper><?xml version="1.0" encoding="UTF-8"?>
47. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
48.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
49. <mapper namespace="com.example.mapper.UserMapper">
50.    
51. </mapper><?xml version="1.0" encoding="UTF-8"?>
52. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
53.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
54. <mapper namespace="com.example.mapper.UserMapper">
55.    
56. </mapper><?xml version="1.0" encoding="UTF-8"?>
57. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
58.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
59. <mapper namespace="com.example.mapper.UserMapper">
60.    
61. </mapper><?xml version="1.0" encoding="UTF-8"?>
62. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
63.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
64. <mapper namespace="com.example.mapper.UserMapper">
65.    
66. </mapper><?xml version="1.0" encoding="UTF-8"?>
67. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
68.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
69. <mapper namespace="com.example.mapper.UserMapper">
70.    
71. </mapper>AND age = #{age}<?xml version="1.0" encoding="UTF-8"?>
72. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
73.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
74. <mapper namespace="com.example.mapper.UserMapper">
75.    
76. </mapper><?xml version="1.0" encoding="UTF-8"?>
77. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
78.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
79. <mapper namespace="com.example.mapper.UserMapper">
80.    
81. </mapper><?xml version="1.0" encoding="UTF-8"?>
82. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
83.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
84. <mapper namespace="com.example.mapper.UserMapper">
85.    
86. </mapper>

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• 当name为非空,会添加AND name LIKE CONCAT('%', #{name}, '%') 当age为非空时会添加 AND age = #{age}
  
• 结合标签使用,能自动处理首个AND,使得SQL语句正确
  

• 其作用在于动态拼接SQL片段前添加或去除特点字符,比如前缀,后缀,以及多余的分隔符如,
  
• 常用于INSERT和UPDATE语句,避免出现多余逗号
  

INSERT语句

1. <?xml version="1.0" encoding="UTF-8"?>
2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
4. <mapper namespace="com.example.mapper.UserMapper">
5.    
6. </mapper>INSERT INTO user<?xml version="1.0" encoding="UTF-8"?>
7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
9. <mapper namespace="com.example.mapper.UserMapper">
10.    
11. </mapper><?xml version="1.0" encoding="UTF-8"?>
12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
14. <mapper namespace="com.example.mapper.UserMapper">
15.    
16. </mapper><?xml version="1.0" encoding="UTF-8"?>
17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
19. <mapper namespace="com.example.mapper.UserMapper">
20.    
21. </mapper>name,<?xml version="1.0" encoding="UTF-8"?>
22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
24. <mapper namespace="com.example.mapper.UserMapper">
25.    
26. </mapper><?xml version="1.0" encoding="UTF-8"?>
27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
29. <mapper namespace="com.example.mapper.UserMapper">
30.    
31. </mapper>age,<?xml version="1.0" encoding="UTF-8"?>
32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
34. <mapper namespace="com.example.mapper.UserMapper">
35.    
36. </mapper><?xml version="1.0" encoding="UTF-8"?>
37. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
38.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
39. <mapper namespace="com.example.mapper.UserMapper">
40.    
41. </mapper>email,<?xml version="1.0" encoding="UTF-8"?>
42. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
43.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
44. <mapper namespace="com.example.mapper.UserMapper">
45.    
46. </mapper><?xml version="1.0" encoding="UTF-8"?>
47. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
48.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
49. <mapper namespace="com.example.mapper.UserMapper">
50.    
51. </mapper>VALUES<?xml version="1.0" encoding="UTF-8"?>
52. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
53.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
54. <mapper namespace="com.example.mapper.UserMapper">
55.    
56. </mapper><?xml version="1.0" encoding="UTF-8"?>
57. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
58.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
59. <mapper namespace="com.example.mapper.UserMapper">
60.    
61. </mapper><?xml version="1.0" encoding="UTF-8"?>
62. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
63.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
64. <mapper namespace="com.example.mapper.UserMapper">
65.    
66. </mapper>#{name},<?xml version="1.0" encoding="UTF-8"?>
67. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
68.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
69. <mapper namespace="com.example.mapper.UserMapper">
70.    
71. </mapper><?xml version="1.0" encoding="UTF-8"?>
72. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
73.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
74. <mapper namespace="com.example.mapper.UserMapper">
75.    
76. </mapper>#{age},<?xml version="1.0" encoding="UTF-8"?>
77. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
78.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
79. <mapper namespace="com.example.mapper.UserMapper">
80.    
81. </mapper><?xml version="1.0" encoding="UTF-8"?>
82. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
83.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
84. <mapper namespace="com.example.mapper.UserMapper">
85.    
86. </mapper>#{email},<?xml version="1.0" encoding="UTF-8"?>
87. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
88.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
89. <mapper namespace="com.example.mapper.UserMapper">
90.    
91. </mapper>

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• 标签包裹字段列表和对应值部分
  
• suffixOverrides=”,” 表示自动去除多余的逗号,确保sql语法正确
  

UPDATE语句

• 标签是的特性化
  

1. <?xml version="1.0" encoding="UTF-8"?>
2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
4. <mapper namespace="com.example.mapper.UserMapper">
5.    
6. </mapper>UPDATE user<?xml version="1.0" encoding="UTF-8"?>
7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
9. <mapper namespace="com.example.mapper.UserMapper">
10.    
11. </mapper><?xml version="1.0" encoding="UTF-8"?>
12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
14. <mapper namespace="com.example.mapper.UserMapper">
15.    
16. </mapper><?xml version="1.0" encoding="UTF-8"?>
17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
19. <mapper namespace="com.example.mapper.UserMapper">
20.    
21. </mapper>name = #{name},<?xml version="1.0" encoding="UTF-8"?>
22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
24. <mapper namespace="com.example.mapper.UserMapper">
25.    
26. </mapper><?xml version="1.0" encoding="UTF-8"?>
27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
29. <mapper namespace="com.example.mapper.UserMapper">
30.    
31. </mapper>age = #{age},<?xml version="1.0" encoding="UTF-8"?>
32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
34. <mapper namespace="com.example.mapper.UserMapper">
35.    
36. </mapper><?xml version="1.0" encoding="UTF-8"?>
37. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
38.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
39. <mapper namespace="com.example.mapper.UserMapper">
40.    
41. </mapper>email = #{email},<?xml version="1.0" encoding="UTF-8"?>
42. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
43.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
44. <mapper namespace="com.example.mapper.UserMapper">
45.    
46. </mapper><?xml version="1.0" encoding="UTF-8"?>
47. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
48.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
49. <mapper namespace="com.example.mapper.UserMapper">
50.    
51. </mapper>WHERE id = #{id}

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• 标签内部原理类似,会自动去除多余逗号
  

• 用于遍历集合,数组和Map,常用于批量操作或动态生成IN子句
  
• 其主要属性
  
  
  
  • collection:集合或数组名称(可用@Param()指定对应名称,默认为list或array)
    
  • item:循环时每个元素的别名
    
  • open:循环生成sql片段的前缀
    
  • separator:循环时的分隔符
    
  • close:循环生成sql片段的后缀
    
  
  

1. <?xml version="1.0" encoding="UTF-8"?>
2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
4. <mapper namespace="com.example.mapper.UserMapper">
5.    
6. </mapper>SELECT * FROM user<?xml version="1.0" encoding="UTF-8"?>
7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
9. <mapper namespace="com.example.mapper.UserMapper">
10.    
11. </mapper><?xml version="1.0" encoding="UTF-8"?>
12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
14. <mapper namespace="com.example.mapper.UserMapper">
15.    
16. </mapper><?xml version="1.0" encoding="UTF-8"?>
17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
19. <mapper namespace="com.example.mapper.UserMapper">
20.    
21. </mapper><?xml version="1.0" encoding="UTF-8"?>
22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
24. <mapper namespace="com.example.mapper.UserMapper">
25.    
26. </mapper><?xml version="1.0" encoding="UTF-8"?>
27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
29. <mapper namespace="com.example.mapper.UserMapper">
30.    
31. </mapper><?xml version="1.0" encoding="UTF-8"?>
32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
34. <mapper namespace="com.example.mapper.UserMapper">
35.    
36. </mapper>AND id IN<?xml version="1.0" encoding="UTF-8"?>
37. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
38.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
39. <mapper namespace="com.example.mapper.UserMapper">
40.    
41. </mapper><?xml version="1.0" encoding="UTF-8"?>
42. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
43.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
44. <mapper namespace="com.example.mapper.UserMapper">
45.    
46. </mapper><?xml version="1.0" encoding="UTF-8"?>
47. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
48.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
49. <mapper namespace="com.example.mapper.UserMapper">
50.    
51. </mapper><?xml version="1.0" encoding="UTF-8"?>
52. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
53.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
54. <mapper namespace="com.example.mapper.UserMapper">
55.    
56. </mapper><?xml version="1.0" encoding="UTF-8"?>
57. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
58.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
59. <mapper namespace="com.example.mapper.UserMapper">
60.    
61. </mapper><?xml version="1.0" encoding="UTF-8"?>
62. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
63.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
64. <mapper namespace="com.example.mapper.UserMapper">
65.    
66. </mapper><?xml version="1.0" encoding="UTF-8"?>
67. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
68.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
69. <mapper namespace="com.example.mapper.UserMapper">
70.    
71. </mapper>#{id}<?xml version="1.0" encoding="UTF-8"?>
72. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
73.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
74. <mapper namespace="com.example.mapper.UserMapper">
75.    
76. </mapper><?xml version="1.0" encoding="UTF-8"?>
77. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
78.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
79. <mapper namespace="com.example.mapper.UserMapper">
80.    
81. </mapper><?xml version="1.0" encoding="UTF-8"?>
82. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
83.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
84. <mapper namespace="com.example.mapper.UserMapper">
85.    
86. </mapper><?xml version="1.0" encoding="UTF-8"?>
87. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
88.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
89. <mapper namespace="com.example.mapper.UserMapper">
90.    
91. </mapper><?xml version="1.0" encoding="UTF-8"?>
92. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
93.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
94. <mapper namespace="com.example.mapper.UserMapper">
95.    
96. </mapper><?xml version="1.0" encoding="UTF-8"?>
97. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
98.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
99. <mapper namespace="com.example.mapper.UserMapper">
100.    
101. </mapper>

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• 当ids不为null时,进入生成的sql片段为 SELECT * FROM AND  WHERE id IN(#{id},#{id},…)
  
• 其中标签遍历集合ids,用逗号进行分隔,并在开头添加(括号,结尾添加)括号
  
• 最终标签会去除第一个AND,使sql合法SELECT * FROM id WHERE IN(#{id},#{id},…)
  

MyBatis的映射

基本映射

用于单一的字段对应

• 假设有一个user表,其中有字段id,name,age其在Java中有个简单的对应类User,其属性分别也是id,name,age那么在Mapper.xml进行select查询时
  1. SELECT id, name, age FROM user WHERE id = #{id}

  复制代码
• MyBatis会将查询的结果中每一列值自动赋值给User对象中相同的属性
  
  
  
  • 数据库列表的id→User对象的id
    
  • 数据库列表的name→User对象的name
    
  • 数据库列表的age→User对象的age
    
  
  
• 这样可能就会出现一种情况,数据库列表的列名与对象的属性名不一致,通常使用开启驼峰转换来解决→在application.yml的mybatis配置中添加如下配置:
  1. mybatis:<?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>map-underscore-to-camel-case: true

  复制代码

一对一映射

当查询中需要查询一个对象时

• 现假设,数据库有两张表一个user(用户)表,另一个user_detail(用户详细信息)表,在Java中我们可以创建两个类User和UserDetail类
  
• 然后再创建一个UserVo类,其中包含User的属性和一个UserDatail对象
  

1. public class User {<?xml version="1.0" encoding="UTF-8"?>
2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
4. <mapper namespace="com.example.mapper.UserMapper">
5.    
6. </mapper>private Integer id;<?xml version="1.0" encoding="UTF-8"?>
7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
9. <mapper namespace="com.example.mapper.UserMapper">
10.    
11. </mapper>private String name;<?xml version="1.0" encoding="UTF-8"?>
12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
14. <mapper namespace="com.example.mapper.UserMapper">
15.    
16. </mapper>private Integer age;}public class UserDetail {<?xml version="1.0" encoding="UTF-8"?>
17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
19. <mapper namespace="com.example.mapper.UserMapper">
20.    
21. </mapper>private Integer detailId;<?xml version="1.0" encoding="UTF-8"?>
22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
24. <mapper namespace="com.example.mapper.UserMapper">
25.    
26. </mapper>private String address;<?xml version="1.0" encoding="UTF-8"?>
27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
29. <mapper namespace="com.example.mapper.UserMapper">
30.    
31. </mapper>private String phone;}public class UserVo {<?xml version="1.0" encoding="UTF-8"?>
32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
34. <mapper namespace="com.example.mapper.UserMapper">
35.    
36. </mapper>private Integer id;<?xml version="1.0" encoding="UTF-8"?>
37. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
38.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
39. <mapper namespace="com.example.mapper.UserMapper">
40.    
41. </mapper>private String name;<?xml version="1.0" encoding="UTF-8"?>
42. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
43.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
44. <mapper namespace="com.example.mapper.UserMapper">
45.    
46. </mapper>private Integer age;<?xml version="1.0" encoding="UTF-8"?>
47. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
48.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
49. <mapper namespace="com.example.mapper.UserMapper">
50.    
51. </mapper>private UserDetail userDetail;  // 一对一关系：一个用户对应一份详细信息 }

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XML配置如下:

1. <?xml version="1.0" encoding="UTF-8"?>
2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
4. <mapper namespace="com.example.mapper.UserMapper">
5.    
6. </mapper><?xml version="1.0" encoding="UTF-8"?>
7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
9. <mapper namespace="com.example.mapper.UserMapper">
10.    
11. </mapper><?xml version="1.0" encoding="UTF-8"?>
12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
14. <mapper namespace="com.example.mapper.UserMapper">
15.    
16. </mapper><?xml version="1.0" encoding="UTF-8"?>
17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
19. <mapper namespace="com.example.mapper.UserMapper">
20.    
21. </mapper><?xml version="1.0" encoding="UTF-8"?>
22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
24. <mapper namespace="com.example.mapper.UserMapper">
25.    
26. </mapper><?xml version="1.0" encoding="UTF-8"?>
27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
29. <mapper namespace="com.example.mapper.UserMapper">
30.    
31. </mapper><?xml version="1.0" encoding="UTF-8"?>
32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
34. <mapper namespace="com.example.mapper.UserMapper">
35.    
36. </mapper><?xml version="1.0" encoding="UTF-8"?>
37. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
38.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
39. <mapper namespace="com.example.mapper.UserMapper">
40.    
41. </mapper><?xml version="1.0" encoding="UTF-8"?>
42. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
43.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
44. <mapper namespace="com.example.mapper.UserMapper">
45.    
46. </mapper><?xml version="1.0" encoding="UTF-8"?>
47. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
48.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
49. <mapper namespace="com.example.mapper.UserMapper">
50.    
51. </mapper><?xml version="1.0" encoding="UTF-8"?>
52. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
53.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
54. <mapper namespace="com.example.mapper.UserMapper">
55.    
56. </mapper><?xml version="1.0" encoding="UTF-8"?>
57. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
58.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
59. <mapper namespace="com.example.mapper.UserMapper">
60.    
61. </mapper><?xml version="1.0" encoding="UTF-8"?>
62. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
63.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
64. <mapper namespace="com.example.mapper.UserMapper">
65.    
66. </mapper>SELECT u.id, u.name, u.age, ud.detail_id, ud.address, ud.phone<?xml version="1.0" encoding="UTF-8"?>
67. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
68.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
69. <mapper namespace="com.example.mapper.UserMapper">
70.    
71. </mapper>FROM user u<?xml version="1.0" encoding="UTF-8"?>
72. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
73.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
74. <mapper namespace="com.example.mapper.UserMapper">
75.    
76. </mapper>LEFT JOIN user_detail ud ON u.id = ud.user_id<?xml version="1.0" encoding="UTF-8"?>
77. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
78.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
79. <mapper namespace="com.example.mapper.UserMapper">
80.    
81. </mapper>WHERE u.id = #{id}

复制代码

• 标签
  
  
  
  • 用于定义一组映射规则,将查询的结果转换为一个指定类型的Java对象
    
  • 属性
    
    
    
    • id:为该映射指定一个唯一标识,供其在XML中引用使用,如
      
    • type:指定映射结果对应的Java类型(对象的全路径)
      
    
    
  
  
• 标签
  
  
  
  • 用于将数据库列映射到Java对象的属性,在中使用
    
  • 属性
    
    
    
    • property:Java对象中的属性名称,如其表示将查询到的user_name列的值赋值给userName属性
      
    • cloumn:数据库查询结果中的列名,如column="user_name”表示sql查询列名为user_name的值
      
    
    
  
  
• 标签
  
  
  
  • 类似于主要用于映射主键字段
    
  • 属性
    
    
    
    • property:与相同,映射到Java对象的主键属性
      
    • column:对应数据库中的主键列名
      
    
    
  
  
• 标签
  
  
  
  • 表示一个一对一关连
    
  • 当查询到结果时,MyBatis会将用户的基本字段{id,name,age}直接映射到UserVo中,同时将详细信息{detail_id,address,phone}封装为一个UserDetail对象,并赋值到UserVo的userDetail对象中
    
  
  

一对多映射

提供用于有列表对象的查询

• 现假设一个老师(Teacher)类和一个学生(student)类,一个老师可以对应多个学生,在Java中我们可以设计Teacher类, 使用List属性来存放老师的所有学生
  1. public class Teacher {<?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper>private Integer id;<?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper>private String teacherName;<?xml version="1.0" encoding="UTF-8"?>
  12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  14. <mapper namespace="com.example.mapper.UserMapper">
  15.    
  16. </mapper>private Integer age;<?xml version="1.0" encoding="UTF-8"?>
  17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  19. <mapper namespace="com.example.mapper.UserMapper">
  20.    
  21. </mapper>private List students; // 一对多关系：一个老师对应多个学生}public class Student {<?xml version="1.0" encoding="UTF-8"?>
  22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  24. <mapper namespace="com.example.mapper.UserMapper">
  25.    
  26. </mapper>private Integer id;<?xml version="1.0" encoding="UTF-8"?>
  27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  29. <mapper namespace="com.example.mapper.UserMapper">
  30.    
  31. </mapper>private String name;<?xml version="1.0" encoding="UTF-8"?>
  32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  34. <mapper namespace="com.example.mapper.UserMapper">
  35.    
  36. </mapper>private Integer age;}

  复制代码
  XML配置如下:
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  3.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.example.mapper.UserMapper">
  5.    
  6. </mapper><?xml version="1.0" encoding="UTF-8"?>
  7. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  8.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  9. <mapper namespace="com.example.mapper.UserMapper">
  10.    
  11. </mapper><?xml version="1.0" encoding="UTF-8"?>
  12. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  13.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  14. <mapper namespace="com.example.mapper.UserMapper">
  15.    
  16. </mapper><?xml version="1.0" encoding="UTF-8"?>
  17. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  18.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  19. <mapper namespace="com.example.mapper.UserMapper">
  20.    
  21. </mapper><?xml version="1.0" encoding="UTF-8"?>
  22. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  23.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  24. <mapper namespace="com.example.mapper.UserMapper">
  25.    
  26. </mapper><?xml version="1.0" encoding="UTF-8"?>
  27. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  28.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  29. <mapper namespace="com.example.mapper.UserMapper">
  30.    
  31. </mapper><?xml version="1.0" encoding="UTF-8"?>
  32. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  33.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  34. <mapper namespace="com.example.mapper.UserMapper">
  35.    
  36. </mapper><?xml version="1.0" encoding="UTF-8"?>
  37. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  38.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  39. <mapper namespace="com.example.mapper.UserMapper">
  40.    
  41. </mapper><?xml version="1.0" encoding="UTF-8"?>
  42. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  43.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  44. <mapper namespace="com.example.mapper.UserMapper">
  45.    
  46. </mapper><?xml version="1.0" encoding="UTF-8"?>
  47. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  48.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  49. <mapper namespace="com.example.mapper.UserMapper">
  50.    
  51. </mapper><?xml version="1.0" encoding="UTF-8"?>
  52. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  53.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  54. <mapper namespace="com.example.mapper.UserMapper">
  55.    
  56. </mapper><?xml version="1.0" encoding="UTF-8"?>
  57. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  58.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  59. <mapper namespace="com.example.mapper.UserMapper">
  60.    
  61. </mapper><?xml version="1.0" encoding="UTF-8"?>
  62. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  63.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  64. <mapper namespace="com.example.mapper.UserMapper">
  65.    
  66. </mapper>SELECT t.id as teacher_id, t.teacher_name, t.age as teacher_age,<?xml version="1.0" encoding="UTF-8"?>
  67. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  68.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  69. <mapper namespace="com.example.mapper.UserMapper">
  70.    
  71. </mapper><?xml version="1.0" encoding="UTF-8"?>
  72. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  73.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  74. <mapper namespace="com.example.mapper.UserMapper">
  75.    
  76. </mapper>   s.id as student_id, s.name as student_name, s.age as student_age<?xml version="1.0" encoding="UTF-8"?>
  77. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  78.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  79. <mapper namespace="com.example.mapper.UserMapper">
  80.    
  81. </mapper>FROM teacher t<?xml version="1.0" encoding="UTF-8"?>
  82. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  83.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  84. <mapper namespace="com.example.mapper.UserMapper">
  85.    
  86. </mapper>LEFT JOIN student s ON t.id = s.teacher_id<?xml version="1.0" encoding="UTF-8"?>
  87. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  88.     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  89. <mapper namespace="com.example.mapper.UserMapper">
  90.    
  91. </mapper>WHERE t.id = #{id}

  复制代码
  
  
  • 标签:用于表示一对多关系,把查询结果中的学生记录封装成一个列表,并赋值到Teacher对象中的student属性
    
  
  

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