某大型企业，集团公司旗下有若干子公司，每个公司一名 CEO。同时，集团文件要求各子公司的 CEO 不得兼任。此时，CEO 与子公司的关系就是一对一的，分别对 CEO 和公司进行建模。要求输入公司 ID 即可查询到该公司的信息，包括 CEO 详细信息。
二 操作步骤 2.1 新建项目mvn archetype:generate -DgroupId=com.ivandu.mybatis -D artifactId=mybatis -DarchetypeArtifactId=maven-archetype-quickstart2.2 关联远程已有仓库
git init git add . git commit -m "一对一" git remote add origin https://github.com/cxwn/mybatis.git git push -u -f origin master2.3 创建数据库、表
根据背景描述，我们可以创建如下两张表：
create table ceo
(
id_ceo int primary key auto_increment, -- ID
name_ceo varchar(20), -- 姓名
age_ceo int -- 年龄
);
insert into ceo(name_ceo, age_ceo)
values ('John', 39);
insert into ceo(name_ceo, age_ceo)
values ('Bill', 45);
insert into ceo(name_ceo, age_ceo)
values ('Musk', 40);
create table company
(
id_com int primary key auto_increment, -- 公司ID
name_com varchar(20), -- 公司名称
id_ceo_com int unique,
foreign key (id_ceo_com) references ceo (id_ceo)
);
insert into company(name_com, id_ceo_com)
values ('ChinaACompany', 1);
insert into company(name_com, id_ceo_com)
values ('ChinaCCompany', 3);
insert into company(name_com, id_ceo_com)
values ('ChinaBCompany', 2);
2.4 项目配置
2.4.1 pom.xml
2.4.2 src/resources/mybatis.cfg.xml4.0.0 com.ivandu.mybatis mybatis jar 1.0.0 mybatis UTF-8 11 11 11 org.mybatis mybatis 3.5.7 mysql mysql-connector-java 8.0.26 log4j log4j 1.2.17 junit junit 4.13.2 test org.apache.maven.plugins maven-compiler-plugin 3.8.0 src/main/java ***.*
2.4.3 src/resources/log4j.properties
# Global logging configuration log4j.rootLogger=INFO, stdout # Console output... log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.layout=org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n2.5 创建实例类 Model 2.5.1 CEO 类
package com.ivandu.mybatis.model;
public class CEO {
private Integer id;
private String name;
private Integer age;
public CEO(Integer id, String name, Integer age) {
this.id = id;
this.name = name;
this.age = age;
}
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 Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
}
2.5.2 Company 类
package com.ivandu.mybatis.model;
public class Company {
private Integer id;
private String name;
private CEO ceo;
public Company(){}
public Company(Integer id, String name, CEO ceo) {
this.id = id;
this.name = name;
this.ceo = ceo;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getId() {
return this.id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public CEO getCeo() {
return ceo;
}
public void setCeo(CEO ceo) {
this.ceo = ceo;
}
}
2.6 创建 Mapper
2.6.1 CompanyMapper.java
package com.ivandu.mybatis.mapper;
import com.ivandu.mybatis.model.Company;
public interface CompanyMapper {
Company selectCompanyById(Integer id) throws Exception;
}
2.6.2 CompanyMapper.xml
2.7 测试运行
package com.ivandu.mybatis;
import com.ivandu.mybatis.mapper.CompanyMapper;
import com.ivandu.mybatis.model.Company;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.BeforeClass;
import org.junit.Test;
import java.io.InputStream;
public class OneToOneTest {
public static SqlSessionFactory sqlSessionFactory;
@BeforeClass
public static void init() throws Exception{
String resource = "mybatis.cfg.xml";
InputStream reader = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
reader.close();
}
@Test
public void selectCompanyById(){
Company company;
SqlSession sqlSession = sqlSessionFactory.openSession();
try (sqlSession) {
CompanyMapper companyMapper = sqlSession.getMapper(CompanyMapper.class);
company = companyMapper.selectCompanyById(2);
System.out.println(company.getId() + "t" +
company.getName() + "t" +
company.getCeo().getAge() + "t" +
company.getCeo().getId() + "t" +
company.getCeo().getName());
} catch (Exception e) {
e.printStackTrace();
}
}
}
三 总结
3.1 错误及故障排除
Error querying database. Cause: org.apache.ibatis.reflection.ReflectionException: Error instantiating class com.ivandu.mybatis.model.Company with invalid types (Integer,String,CEO) or values (1,ChinaBigCompany,1). Cause: java.lang.IllegalArgumentException: argument type mismatch.
解决：实体类中加入无参构造函数。
GitHub：https://github.com/cxwn/mybatis.git tag:2.0.0
