Mybatis、使用注解的方式编写用户和角色一对多关系，并使用延迟加载

1、数据库准备

CREATE TABLE `role` (

`ID` INT(11) NOT NULL COMMENT '编号',
`ROLE_NAME` VARCHAR(30) DEFAULT NULL COMMENT '角色名称',
`ROLE_DESC` VARCHAR(60) DEFAULT NULL COMMENT '角色描述',
PRIMARY KEY (`ID`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO `role`(`ID`,`ROLE_NAME`,`ROLE_DESC`) VALUES (1,'院长','管理整个学院'),(2,'总裁','管理整个公司'),(3,'校长','管理整个学校');
CREATE TABLE `user` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`username` VARCHAR(32) NOT NULL COMMENT '用户名称',
`birthday` DATETIME DEFAULT NULL COMMENT '生日',
`sex` CHAR(1) DEFAULT NULL COMMENT '性别',
`address` VARCHAR(256) DEFAULT NULL COMMENT '地址',
PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO `user`(`id`,`username`,`birthday`,`sex`,`address`) VALUES (41,'老王','2018-02-27 17:47:08','男','北京'),(42,'小二王','2018-03-02 15:09:37','女','北京金燕龙'),(43,'小二王','2018-03-04 11:34:34','女','北京金燕龙'),(45,'传智播客','2018-03-04 12:04:06','男','北京金燕龙'),(46,'老王','2018-03-07 17:37:26','男','北京'),(48,'小马宝莉','2018-03-08 11:44:00','女','北京修正');

2、创建一个Maven项目

在pom.xml引入约束:

<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>cn.wzq</groupId>
<artifactId>MyBatis_day04_01_note_user_role_onetomany</artifactId>
<version>0.0.1-SNAPSHOT</version>
    <dependencies>
       
       <dependency>
           <groupId>log4j</groupId>
           <artifactId>log4j</artifactId>
           <version>1.2.12</version>
       </dependency>
       
       <dependency>
           <groupId>mysql</groupId>
           <artifactId>mysql-connector-java</artifactId>
           <version>5.1.6</version>
       </dependency>
       
       <dependency>
           <groupId>org.mybatis</groupId>
           <artifactId>mybatis</artifactId>
           <version>3.4.5</version>
       </dependency>
       <dependency>
           <groupId>junit</groupId>
           <artifactId>junit</artifactId>
           <version>4.12</version>
       </dependency>
   </dependencies>
</project>

2、创建数据库信息配置文件：jdbc.properties

jdbc.username=root
jdbc.password=root
jdbc.url=jdbc:mysql://localhost:3306/mybatisdb?characterEncoding=utf8

jdbc.driver=com.mysql.jdbc.Driver

3、配置核心配置文件

<?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>
   
   <properties resource="jdbc.properties"></properties>
   
   <typeAliases>
        <package name="cn.wzq.mybatis.domin"/>
   </typeAliases>
   <environments default="development">
      <environment id="development">
        <transactionManager type="JDBC" />
        <dataSource type="POOLED">
          <property name="driver" value="${jdbc.driver}" ></property>
          <property name="url" value="${jdbc.url}" ></property>
          <property name="username" value="${jdbc.username}"></property>
          <property name="password" value="${jdbc.password}"></property>
        </dataSource>
     </environment>
</environments>

<mappers>
   <package name="cn.wzq.mybatis.dao"/>
</mappers>
</configuration>

4、创建user和role对象

public class User {

   private Integer id;
   private String username;
   private String sex;
   private String address;
   private Date birthday;

private List<Role> list;

//get/set/toString省略；

｝

public class Role {
   private Integer id;
   private String ROLE_NAME;
   private String ROLE_DESC;
    //get/set/toString省略；

｝

5、创建IRoleDao接口

public interface IRoleDao {

   //根据用户查询角色
   @Select(value="select * from role where id = #{id}")
   public Role findRole(int uid);

}

6、创建IUserDao接口

public interface IUserDao {

   //查询用户下的所有角色
   @Select(value="select * from user")
   @Results(value= {
           @Result(property="id",column="id",id=true),
           @Result(property="username",column="username"),
           @Result(property="sex",column="sex"),
           @Result(property="address",column="address"),
           @Result(property="birthday",column="birthday"),
           @Result(property="list",javaType=List.class,column="id",
               many=@Many(select="cn.wzq.mybatis.dao.IRoleDao.findRole",fetchType=FetchType.LAZY)
           )
   })
   public List<User> findAll();

}

7、测试

    //查询用户下所有角色
   @Test
   public void findAllTest() {
       SqlSession openSession = sqlSessionFactory.openSession();
       IUserDao userDao = openSession.getMapper(IUserDao.class);
       List<User> list = userDao.findAll();
       for (User user : list) {
           System.out.println(user.getId());
           //System.out.println(user.getList()); //需要使用时释放注解
       }

}

整体目录结构