(十)Mybatis屬性名與查詢欄位名不相同
阿新 • • 發佈:2018-11-28
注:程式碼已託管在GitHub上,地址是:https://github.com/Damaer/Mybatis-Learning,專案是mybatis-06-resultMap,需要自取,需要配置maven環境以及mysql環境,覺得有用可以點個小星星,小菜鳥在此Thanks~
很多時候我們有這樣的需求,資料庫的欄位名與實體類的屬性名不一致,這個時候我們需要怎麼做呢?有兩種解決方案,第一種:直接在查詢的時候使用別名,將別名設定成與實體類的屬性名一致。第二種:使用resultType,自己定義對映關係。
整個專案的目錄如下:
首先,我們需要搭建資料庫mysql環境(test.sql),id我們寫成了sid,name我們寫成了sname,age我們寫成了sage:
#建立資料庫
CREATE DATABASE `test` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;
#建立資料表
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實體類:
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驅動包 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.29</version>
</dependency>
<!-- junit測試包 -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<!-- 日誌檔案管理包 -->
<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>
主配置檔案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>
<!-- 配置資料庫檔案 -->
<properties resource="jdbc_mysql.properties">
</properties>
<!-- 別名,對資料物件操作全名太長,需要使用別名 -->
<typeAliases>
<!--<typeAlias type="bean.Student" alias="Student"/>-->
<!--直接使用類名即可,對於整個包的路徑配置(別名),簡單快捷 -->
<package name="bean"/>
</typeAliases>
<!-- 配置執行環境 -->
<!-- default 表示預設使用哪一個環境,可以配置多個,比如開發時的測試環境,上線後的正式環境等 -->
<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>
<!-- 註冊對映檔案 -->
<mappers>
<mapper resource="mapper/mapper.xml"/>
</mappers>
</configuration>
資料庫配置檔案(jdbc_mysql.properties):
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test
jdbc.user=root
jdbc.password=123456
日誌配置檔案 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
使用到的工具類(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;
}
}
介面定義(IStudentDao.java):
public interface IStudentDao {
// 返回所有學生的資訊List
public List<Student> selectAllStudents();
// 根據id查詢學生
public Student selectStudentById(int id);
}
介面實現類(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");
//查詢不用修改,所以不用提交事務
} 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檔案:
可以直接使用別名:
<?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=${value}
</select>
</mapper>
或者可以自己定義對映:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="abc">
<resultMap id="StudentMapper" type="Student">
<id column="sid" property="id"/>
<result column="sname" property="name"/>
<result column="sage" property="age"/>
</resultMap>
<select id="selectAllStudents" resultMap="StudentMapper">
select sid as id,sname as name,sage as age,score from student
</select>
<select id="selectStudentById" resultMap="StudentMapper">
select sid as id,sname as name,sage as age,score from student where sid=${value}
</select>
</mapper>
需要注意的點:
- 有一個id屬性,這個是在其他地方使用的時候的id
- Type - 實體類,可以寫別名,要不就要寫帶全路徑的類名
- id - 標籤是為了標記出作為 ID 的結果可以幫助提高整體效能
- result – 注入到欄位或 JavaBean 屬性的普通結果
- association – 一個複雜型別的關聯;許多結果將包裝成這種型別巢狀結果對映 – 關聯可以指定為一個 resultMap 元素,或者引用一個
- collection – 一個複雜型別的集合
巢狀結果對映 – 集合可以指定為一個 resultMap 元素,或者引用一個- discriminator – 使用結果值來決定使用哪個 resultMap
case – 基於某些值的結果對映
巢狀結果對映 – 一個 case 也是一個對映它本身的結果,因此可以包含很多相 同的元素,或者它可以參照一個外部的 resultMap。
如果物件名與屬性名一致,我們可以不把它寫入
測試類MyTest.class:
public class MyTest {
private IStudentDao dao;
@Before
public void Before(){
dao=new StudentDaoImpl();
}
/*
* 查詢列表
*
*/
@Test
public void testselectList(){
List<Student> students=dao.selectAllStudents();
if(students.size()>0){
for(Student student:students){
System.out.println(student);
}
}
}
/*
* 通過id來查詢student
*
*/
@Test
public void testselectStudentById(){
Student student=dao.selectStudentById(1);
System.out.println(student);
}
}