MyBatis：註解簡化一對一關係
阿新 • • 發佈：2018-11-08
註解式是真的好用！
一對一的關係：客戶擁有一張身份證，而身份證也只有一個客戶。
客戶表中有身份證的cid，可以通過這個cid匹配身份證表中的cid，拿到那個具體的身份證資訊
反之，身份證通過本身的cid匹配客戶表中的cid，以此得到客戶的資訊。
/* Navicat MySQL Data Transfer Source Server : hc Source Server Version : 50723 Source Host : localhost:3306 Source Database : cn Target Server Type : MYSQL Target Server Version : 50723 File Encoding : 65001 Date: 2018-11-07 15:32:01 */ SET FOREIGN_KEY_CHECKS=0; -- ---------------------------- -- Table structure for `person` -- ---------------------------- DROP TABLE IF EXISTS `person`; CREATE TABLE `person` ( `perId` int(11) NOT NULL AUTO_INCREMENT, `perName` varchar(255) DEFAULT NULL, `cardId` int(11) NOT NULL, PRIMARY KEY (`perId`) ) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of person -- ---------------------------- INSERT INTO `person` VALUES ('1', 'haha', '1'); INSERT INTO `person` VALUES ('2', '維爾瓦', '2'); INSERT INTO `person` VALUES ('3', '阿三', '3'); INSERT INTO `person` VALUES ('4', '32阿瑟東', '4'); INSERT INTO `person` VALUES ('5', '安撫', '5');
MYsql中的表，copy後匯入資料庫即可。
<dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.1</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.43</version> </dependency>
pom.xml
package com.hc.model; public class Person { private int perId; private String perName; private Card card; public Person() { } public Person(String perName) { this.perName = perName; } public int getPerId() { return perId; } public void setPerId(int perId) { this.perId = perId; } public String getPerName() { return perName; } public void setPerName(String perName) { this.perName = perName; } public Card getCard() { return card; } public void setCard(Card card) { this.card = card; } }
Person類
package com.hc.model;
public class Card {
private int cardId;
private String cardName;
private Person person;
public Card() {
}
public Card(String cardName) {
this.cardName = cardName;
}
public int getCardId() {
return cardId;
}
public void setCardId(int cardId) {
this.cardId = cardId;
}
public String getCardName() {
return cardName;
}
public void setCardName(String cardName) {
this.cardName = cardName;
}
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
}
卡類
package com.hc.mapper;
import com.hc.model.Person;
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import java.util.List;
public interface PersonMapper {
@Select("select * from Person")
@Results({
@Result(property = "card",column = "cardId",one = @One(select = "com.hc.mapper.CardMapper.selectCardByCid"))
})
public List<Person> allPerson();
@Select("select * from Person where cardId=#{cardId}")
public Person selectPersonByCid(int cardId);
}
person的MApper
person中有card的物件屬性，
Results中的Result，property 為物件屬性名，column 為關聯的id，
因為person與card相關聯的就是cardid
把cid傳給關聯物件Mapper中的方法，並獲得需要的資料
one相對應的是一個物件，如果是多個，即為many
@one中的select固定，呼叫關聯物件Mapper中的方法
package com.hc.mapper;
import com.hc.model.Card;
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import java.util.List;
public interface CardMapper {
@Select("select * from Card where cardId=#{cardId}")
public Card selectCardByCid(int cardId);
@Select("select * from Card")
@Results({
@Result(id = true,property = "cardId",column = "cardId"),
// 關聯 id 必須
@Result(property = "person",column = "cardId",one = @One(select = "com.hc.mapper.PersonMapper.selectPersonByCid"))
})
public List<Card> allCard();
}
卡的Mapper
selectCardByCid：看似只是一個條件查詢，其實可以被Person mapper中的一對一方法@one呼叫
第二個方法，cardid是必須要拿到的，宣告id=true
否則，最終的資料中拿不到這個cid
但是，不宣告，又能拿到card物件，只是cid為0
<?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>
<typeAliases>
<package name="com.hc.model"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/cn?characterEncoding=utf-8"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper class="com.hc.mapper.UserMapper"/>
<mapper class="com.hc.mapper.PersonMapper"/>
<mapper class="com.hc.mapper.CardMapper"/>
<mapper class="com.hc.mapper.AuthorMapper"/>
<mapper class="com.hc.mapper.BookMapper"/>
<mapper class="com.hc.mapper.CourseMapper"/>
<mapper class="com.hc.mapper.StudentMapper"/>
</mappers>
</configuration>mybatis-config.xml
物件Mapper一定要加到mappers中
package com.hc.test;
import com.hc.mapper.CardMapper;
import com.hc.mapper.PersonMapper;
import com.hc.model.Card;
import com.hc.model.Person;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
public class TestPerson {
private SqlSession session;
@Before
public void before() {
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(getClass().getClassLoader().getResourceAsStream("myBatis-config.xml"));
session = factory.openSession();
}
@Test
public void testCard() {
CardMapper cardMapper = session.getMapper(CardMapper.class);
for (Card card : cardMapper.allCard()) {
System.out.println(card.getCardId() + "\t《" + card.getCardName() + "》");
Person person = card.getPerson();
System.out.println(person.getPerId() + "\t" + person.getPerName());
System.out.println("");
}
}
@Test
public void testPerson() {
PersonMapper personMapper;
personMapper = session.getMapper(PersonMapper.class);
for (Person person : personMapper.allPerson()) {
System.out.println(person.getPerId() + "\t" + person.getPerName());
Card card = person.getCard();
System.out.println(card.getCardId() + "\t《" + card.getCardName() + "》");
System.out.println("");
}
}
@After
public void after() {
session.commit();
session.close();
}
}
單元測試
第二個測試方法：拿到所有person，並通過person表的cid，去卡表拿到相對應的card物件。
第一個方法：
拿到所有的card，通過本身的cid，匹配person的cid，取得person物件。