（十）Mybatis属性名与查询字段名不相同
注：代码已托管在GitHub上，地址是：https://github.com/Damaer/Mybatis-Learning，项目是mybatis-06-resultMap，需要自取，需要配置maven环境以及mysql环境，觉得有用可以点个小星星，小菜鸟在此Thanks~
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：
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:
<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>4.0.0modelVersion>
<groupId>com.testgroupId>
<artifactId>testartifactId>
<version>1.0-SNAPSHOTversion>
<dependencies>
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.3.0version>
dependency>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>5.1.29version>
dependency>
<dependency>
<groupId>junitgroupId>
<artifactId>junitartifactId>
<version>4.11version>
<scope>testscope>
dependency>
<dependency>
<groupId>log4jgroupId>
<artifactId>log4jartifactId>
<version>1.2.17version>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>slf4j-apiartifactId>
<version>1.7.12version>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>slf4j-log4j12artifactId>
<version>1.7.12version>
dependency>
dependencies>
project>主配置文件mybatis.xml:
<configuration>
<properties resource="jdbc_mysql.properties">
properties>
<typeAliases>
<package name="bean"/>
typeAliases>
<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>
<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
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 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 selectAllStudents() {
List 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：
<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=${value}
select>
mapper>或者可以自己定义映射：
<mapper namespace="abc">
<resultMap id="StudentMapper" type="Student">
<id column="sid" property="id"/>
<result column="sname" property="name"/>
<result column="sage" property="age"/>
resultMap>
<select id="selectAllStudents" resultMap="StudentMapper">
select sid as id,sname as name,sage as age,score from student
select>
<select id="selectStudentById" resultMap="StudentMapper">
select sid as id,sname as name,sage as age,score from student where sid=${value}
select>
mapper>
需要注意的点：
- 有一个id属性，这个是在其他地方使用的时候的id
- Type - 实体类，可以写别名，要不就要写带全路径的类名
- id - 标签是为了标记出作为 ID 的结果可以帮助提高整体性能
- result – 注入到字段或 JavaBean 属性的普通结果
- association – 一个复杂类型的关联;许多结果将包装成这种类型嵌套结果映射 – 关联可以指定为一个 resultMap 元素，或者引用一个
- collection – 一个复杂类型的集合
嵌套结果映射 – 集合可以指定为一个 resultMap 元素，或者引用一个- discriminator – 使用结果值来决定使用哪个 resultMap
case – 基于某些值的结果映射
嵌套结果映射 – 一个 case 也是一个映射它本身的结果,因此可以包含很多相 同的元素，或者它可以参照一个外部的 resultMap。
如果对象名与属性名一致，我们可以不把它写入
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 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);
}
}