很多时候咱们有这样的需要，数据库的字段名与实体类的属性名不统一，这个时候咱们须要怎么做呢？有两种解决方案，第一种：间接在查问的时候应用别名，将别名设置成与实体类的属性名统一。第二种：应用resultType，本人定义映射关系。
整个我的项目的目录如下：
首先，咱们须要搭建数据库mysql环境(test.sql),id咱们写成了sid,name咱们写成了sname,age咱们写成了sage：
#创立数据库CREATE DATABASE `test` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;#创立数据表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外围包 --> <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> <!-- 日志文件治理包 --> <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，须要应用别名 --> <typeAliases> <!--<typeAlias type="bean.Student" alias="Student"/>--> <!--间接应用类名即可，对于整个包的门路配置（别名），简略快捷 --> <package name="bean"/> </typeAliases> <!-- 配置运行环境 --> <!-- default 示意默认应用哪一个环境，能够配置多个，比方开发时的测试环境，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.Driverjdbc.url=jdbc:mysql://localhost:3306/test?characterEncoding=utf-8&serverTimezone=UTCjdbc.user=rootjdbc.password=123456日志配置文件 log4j.prperties:
log4j.prpplog4j.rootLogger=DEBUG, stdoutlog4j.appender.stdout=org.apache.log4j.ConsoleAppenderlog4j.appender.stdout.layout=org.apache.log4j.PatternLayoutlog4j.appender.stdout.layout.ConversionPattern=[service] %d - %c -%-4r [%t] %-5p %c %x - %m%nlog4j.logger.java.sql.Statement = debuglog4j.logger.java.sql.PreparedStatement = debuglog4j.logger.java.sql.ResultSet =debug应用到的工具类（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(); // 依据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"); //查问不必批改，所以不必提交事务 } 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; }}最次要的mapper文件：
能够间接应用别名：
<?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=${value} </select></mapper>或者能够本人定义映射：
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="abc"> <resultMap id="StudentMapper" type="Student"> <id column="sid" property="id"/> <result column="sname" property="name"/> <result column="sage" property="age"/> </resultMap> <select id="selectAllStudents" resultMap="StudentMapper"> select sid as id,sname as name,sage as age,score from student </select> <select id="selectStudentById" resultMap="StudentMapper"> select sid as id,sname as name,sage as age,score from student where sid=${value} </select></mapper>
须要留神的点：
- <resultMap></resultMap>有一个id属性，这个是在其余中央应用的时候的id
- Type - 实体类，能够写别名，要不就要写带全门路的类名
- id - 标签是为了标记出作为 ID 的后果能够帮忙进步整体性能
- result – 注入到字段或 JavaBean 属性的一般后果
- association – 一个简单类型的关联;许多后果将包装成这种类型嵌套后果映射 – 关联能够指定为一个 resultMap 元素，或者援用一个
- collection – 一个简单类型的汇合
嵌套后果映射 – 汇合能够指定为一个 resultMap 元素，或者援用一个
- discriminator – 应用后果值来决定应用哪个 resultMap
case – 基于某些值的后果映射
嵌套后果映射 – 一个 case 也是一个映射它自身的后果,因而能够蕴含很多相 同的元素，或者它能够参照一个内部的 resultMap。
如果对象名与属性名统一，咱们能够不把它写入<resultMap></resultMap>
测试类MyTest.class:
public class MyTest { private IStudentDao dao; @Before public void Before(){ dao=new StudentDaoImpl(); } /* * 查问列表 * */ @Test public void testselectList(){ List<Student> students=dao.selectAllStudents(); if(students.size()>0){ for(Student student:students){ System.out.println(student); } } } /* * 通过id来查问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，纵使迟缓，驰而不息。这个世界心愿所有都很快，更快，然而我心愿本人能走好每一步，写好每一篇文章，期待和你们一起交换。
此文章仅代表本人（本菜鸟）学习积攒记录，或者学习笔记，如有侵权，请分割作者核实删除。人无完人，文章也一样，文笔稚嫩，在下不才，勿喷，如果有谬误之处，还望指出，感激不尽~