pom的依赖配置：
1 <dependencies> 2 <dependency> 3 <groupId>org.mybatis</groupId> 4 <artifactId>mybatis</artifactId> 5 <version>3.4.5</version> 6 </dependency> 7 <dependency> 8 <groupId>junit</groupId> 9 <artifactId>junit</artifactId> 10 <version>4.12</version> 11 </dependency> 12 <dependency> 13 <groupId>mysql</groupId> 14 <artifactId>mysql-connector-java</artifactId> 15 <version>8.0.17</version> 16 </dependency> 17 </dependencies>
MySQL数据库的建表语句：
1 CREATE TABLE `tb_user` ( 2 `id` int(11) NOT NULL AUTO_INCREMENT, 3 `username` varchar(32) NOT NULL COMMENT ‘用户名‘, 4 `sex` char(1) DEFAULT NULL COMMENT ‘性别‘, 5 `birthday` date DEFAULT NULL COMMENT ‘生日‘, 6 `address` varchar(256) DEFAULT NULL COMMENT ‘地址‘, 7 PRIMARY KEY (`id`) 8 ) ;
Java实体类代码：
1 public class User {
2
3 private int id;
4 private String name;
5 private String sex;
6 private Date birthday;
7 private String address;
8
9 @Override
10 public String toString() {
11 return "User{" +
12 "id=" + id +
13 ", name=‘" + name + ‘\‘‘ +
14 ", sex=‘" + sex + ‘\‘‘ +
15 ", birthday=" + birthday +
16 ", address=‘" + address + ‘\‘‘ +
17 ‘}‘;
18 }
19
20 public int getId() {
21 return id;
22 }
23
24 public void setId(int id) {
25 this.id = id;
26 }
27
28 public String getName() {
29 return name;
30 }
31
32 public void setName(String name) {
33 this.name = name;
34 }
35
36 public String getSex() {
37 return sex;
38 }
39
40 public void setSex(String sex) {
41 this.sex = sex;
42 }
43
44 public Date getBirthday() {
45 return birthday;
46 }
47
48 public void setBirthday(Date birthday) {
49 this.birthday = birthday;
50 }
51
52 public String getAddress() {
53 return address;
54 }
55
56 public void setAddress(String address) {
57 this.address = address;
58 }
59 }
MyBatis测试方法代码：
1 @Test
2 public void test01() {
3
4 InputStream inputStream = null;
5 try {
6 inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
7 } catch (IOException e) {
8 e.printStackTrace();
9 }
10
11 SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
12
13 SqlSessionFactory factory = builder.build(inputStream);
14
15 SqlSession sqlSession = factory.openSession();
16
17 List<User> list = sqlSession.selectList("test.queryList");
18
19 list.forEach(System.out::println);
20
21 sqlSession.close();
22
23 }
SqlMapConfig的配置：
1 <?xml version="1.0" encoding="UTF-8" ?> 2 <!DOCTYPE configuration 3 PUBLIC "-//mybatis.org//DTD Config 3.0//EN" 4 "http://mybatis.org/dtd/mybatis-3-config.dtd"> 5 <configuration> 6 <environments default="development"> 7 <environment id="development"> 8 <transactionManager type="JDBC" /> 9 <dataSource type="POOLED"> 10 <property name="driver" value="com.mysql.cj.jdbc.Driver"/> 11 <property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis01?serverTimezone=UTC" /> 12 <property name="username" value="root" /> 13 <property name="password" value="root" /> 14 </dataSource> 15 </environment> 16 </environments> 17 18 <mappers> 19 <mapper resource="UserMapper.xml" /> 20 </mappers> 21 </configuration>
UserMapper的配置：
1 <?xml version="1.0" encoding="utf-8" ?> 2 <!DOCTYPE mapper 3 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 4 "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> 5 <mapper namespace="test"> 6 7 <select id="queryList" resultType="com.saika.mybatis.pojo.User"> 8 SELECT * from user 9 </select> 10 11 </mapper>
实体类属性name与表字段username不一致
方案一
采用SQL语句AS起别名的形式，为查询语句的显示列定义别名，让这个别名与实体类的属性名相同以完成自动映射。
SQL语句：
1 SELECT id,username AS name ,sex,birthday,address FROM user
缺点：
1.如果不一致的字段过多会导致语句过长。
2.如果查询语句有多个，每次都要起别名会导致重复代码增多，多次定义显示列增加了工作量。
方案二
修改实体类set方法的方法名对应表字段名。
MyBatis映射的原理就是通过返回的字段名找实体类的setXxx方法进行封装。
Java代码：
1 public void setUsername(String name) {
2 this.name = name;
3 }
方案三
利用<sql>标签提取SQL语句片段统一配置别名，在原查询语句上用<include>标签引入，简化操作。
SQL语句：
1 <sql id="user"> 2 id,username AS name,sex,birthday,address 3 </sql> 4 5 <select id="queryList" resultType="com.saika.mybatis.pojo.User"> 6 SELECT <include refid="user"></include> FROM user 7 </select>
方案四
使用<resultMap>标签配置手动映射。
id 是这个封装规则的唯一标识，用于被查询标签中的resultMap所引用。
type 用于指定将查询结果封装到哪个实体类中。
column是表的字段。
property是实体类的属性。
SQL语句：
1 <resultMap id="userResultMap" type="com.saika.mybatis.pojo.User"> 2 <result column="username" property="name"/> 3 </resultMap> 4 5 <select id="queryList" resultMap="userResultMap"> 6 SELECT id,username,sex,birthday,address FROM user 7 </select>
注解形式：
1 @Result(property ="name",column = "username")
原文地址：https://www.cnblogs.com/manchuria-saika/p/11978096.html
时间： 2024-10-06 22:35:37