【Java】Mybatis【10】-- Mybatis属性名和查询字段名不同怎么做？

很多时候我们有这样的需求，数据库的字段名与实体类的属性名不一致，这个时候我们需要怎么做呢？有两种解决方案，第一种：直接在查询的时候使用别名，将别名设置成与实体类的属性名一致。第二种：使用resultType，自己定义映射关系。
整个项目的目录如下：
【Java】Mybatis【10】-- Mybatis属性名和查询字段名不同怎么做？

首先，我们需要搭建数据库mysql环境(test.sql),id我们写成了sid,name我们写成了sname,age我们写成了sage：

#创建数据库
CREATE DATABASE `test` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;
#创建数据表
CREATE TABLE `student` ( `sid` INT NOT NULL AUTO_INCREMENT , `sname` VARCHAR(20) NOT NULL ,
`sage` INT NOT NULL , `score` DOUBLE NOT NULL , PRIMARY KEY (`sid`)) ENGINE = MyISAM;

Student.class实体类：

public class Student {
private Integer id;
private String name;
private int age;
private double score;
public Student(){
}
public Student(String name, int age, double score) {
super();
this.name = name;
this.age = age;
this.score = score;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public double getScore() {
return score;
}
public void setScore(double score) {
this.score = score;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + ", age=" + age
+ ", score=" + score + "]";
}
}

pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.test</groupId>
<artifactId>test</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<!-- mybatis核心包 -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.3.0</version>
</dependency>
<!-- mysql驱动包 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.21</version>
</dependency>
<!-- junit测试包 -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<!-- 日志文件管理包 -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.12</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.12</version>
</dependency>
</dependencies>
</project>

主配置文件mybatis.xml:

<?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>
<!-- 配置数据库文件 -->
<properties resource="jdbc_mysql.properties">
</properties>
<!-- 别名，对数据对象操作全名太长，需要使用别名 -->
<typeAliases>
<!--<typeAlias type="bean.Student" alias="Student"/>-->
<!--直接使用类名即可，对于整个包的路径配置（别名），简单快捷 -->
<package name="bean"/>
</typeAliases>
<!-- 配置运行环境 -->
<!-- default 表示默认使用哪一个环境，可以配置多个，比如开发时的测试环境，上线后的正式环境等 -->
<environments default="mysqlEM">
<environment id="mysqlEM">
<transactionManager type="JDBC">
</transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.user}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<!-- 注册映射文件 -->
<mappers>
<mapper resource="mapper/mapper.xml"/>
</mappers>
</configuration>

数据库配置文件(jdbc_mysql.properties)：

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test?characterEncoding=utf-8&serverTimezone=UTC
jdbc.user=root
jdbc.password=123456

日志配置文件 log4j.prperties:

log4j.prpp
log4j.rootLogger=DEBUG, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=[service] %d - %c -%-4r [%t] %-5p %c %x - %m%n
log4j.logger.java.sql.Statement = debug
log4j.logger.java.sql.PreparedStatement = debug
log4j.logger.java.sql.ResultSet =debug

使用到的工具类（MyBatisUtils.java）：

public class MyBatisUtils {
static private SqlSessionFactory sqlSessionFactory;
static public SqlSession getSqlSession() {
InputStream is;
try {
is = Resources.getResourceAsStream("mybatis.xml");
if (sqlSessionFactory == null) {
sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
}
return sqlSessionFactory.openSession();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
}

接口定义（IStudentDao.java）：

public interface IStudentDao {
// 返回所有学生的信息List
public List<Student> selectAllStudents();
// 根据id查找学生
public Student selectStudentById(int id);
}

接口实现类(StudentDaoImpl.class)：

public class StudentDaoImpl implements IStudentDao {
private SqlSession sqlSession;
public List<Student> selectAllStudents() {
List<Student> students ;
try {
sqlSession = MyBatisUtils.getSqlSession();
students = sqlSession.selectList("selectAllStudents");
//查询不用修改，所以不用提交事务
} finally {
if (sqlSession != null) {
sqlSession.close();
}
}
return students;
}
public Student selectStudentById(int id) {
Student student=null;
try {
sqlSession=MyBatisUtils.getSqlSession();
student=sqlSession.selectOne("selectStudentById",id);
sqlSession.commit();
} finally{
if(sqlSession!=null){
sqlSession.close();
}
}
return student;
}
}

最主要的mapper文件：

可以直接使用别名：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="abc">
<select id="selectAllStudents" resultType="Student">
select sid as id,sname as name,sage as age,score from student
</select>
<select id="selectStudentById" resultType="Student">
select sid as id,sname as name,sage as age,score from student where sid=${value}
</select>
</mapper>

或者可以自己定义映射：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="abc">
<resultMap id="StudentMapper" type="Student">
<id column="sid" property="id"/>
<result column="sname" property="name"/>
<result column="sage" property="age"/>
</resultMap>
<select id="selectAllStudents" resultMap="StudentMapper">
select sid as id,sname as name,sage as age,score from student
</select>
<select id="selectStudentById" resultMap="StudentMapper">
select sid as id,sname as name,sage as age,score from student where sid=${value}
</select>
</mapper>

【Java】Mybatis【10】-- Mybatis属性名和查询字段名不同怎么做？

需要注意的点：

测试类MyTest.class:

public class MyTest {
private IStudentDao dao;
@Before
public void Before(){
dao=new StudentDaoImpl();
}
/*
* 查询列表
*
*/
@Test
public void testselectList(){
List<Student> students=dao.selectAllStudents();
if(students.size()>0){
for(Student student:students){
System.out.println(student);
}
}
}
/*
* 通过id来查询student
*
*/
@Test
public void testselectStudentById(){
Student student=dao.selectStudentById(1);
System.out.println(student);
}
}

【作者简介】：
秦怀，公众号【秦怀杂货店】作者，技术之路不在一时，山高水长，纵使缓慢，驰而不息。这个世界希望一切都很快，更快，但是我希望自己能走好每一步，写好每一篇文章，期待和你们一起交流。

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