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Mybatis使用@one和@Many实现一对一及一对多关联查询

程序员文章站 2022-04-07 23:30:24
目录二、使用@one注解实现一对一关联查询三、使用@many注解实现一对多关联查询四、fetchtype.lazy 和 fetchtype.eager的区别一、准备工作1.创建springboot项目...

一、准备工作

1.创建springboot项目,项目结构如下

Mybatis使用@one和@Many实现一对一及一对多关联查询

2.添加pom.xml配置信息

<dependencies>
        <dependency>
            <groupid>org.mybatis</groupid>
            <artifactid>mybatis</artifactid>
            <version>3.4.2</version>
        </dependency>

        <dependency>
            <groupid>org.mybatis.spring.boot</groupid>
            <artifactid>mybatis-spring-boot-starter</artifactid>
            <version>1.3.0</version>
        </dependency>

        <dependency>
            <groupid>mysql</groupid>
            <artifactid>mysql-connector-java</artifactid>
            <version>5.1.34</version>
        </dependency>
    </dependencies>

3.配置相关信息

将默认的application.properties文件的后缀修改为“.yml”,即配置文件名称为:application.yml,并配置以下信息:

spring:
  #datasource数据源
  datasource:
    url: jdbc:mysql://localhost:3306/mybatis_test?usessl=false&amp
    username: root
    password: root
    driver-class-name: com.mysql.jdbc.driver

#mybatis配置
mybatis:
  type-aliases-package: com.mye.hl07mybatis.api.pojo #别名定义
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.stdoutimpl #指定 mybatis 所用日志的具体实现,未指定时将自动查找
    map-underscore-to-camel-case: true #开启自动驼峰命名规则(camel case)映射
    lazy-loading-enabled: true #开启延时加载开关
    aggressive-lazy-loading: false #将积极加载改为消极加载(即按需加载),默认值就是false
    lazy-load-trigger-methods: "" #阻挡不相干的操作触发,实现懒加载
    cache-enabled: true #打开全局缓存开关(二级环境),默认值就是true

二、使用@one注解实现一对一关联查询

需求:获取用户信息,同时获取一对多关联的权限列表

1.在mysql数据库中创建用户信息表(tb_user)

-- 判断数据表是否存在,存在则删除
drop table if exists tb_user;
 
-- 创建“用户信息”数据表
create table if not exists tb_user
( 
	user_id int auto_increment primary key comment '用户编号',
	user_account varchar(50) not null comment '用户账号',
	user_password varchar(50) not null comment '用户密码',
	blog_url varchar(50) not null comment '博客地址',
	remark varchar(50) comment '备注'
) comment = '用户信息表';
 
-- 添加数据
insert into tb_user(user_account,user_password,blog_url,remark) values('拒绝熬夜啊的博客','123456','https://blog.csdn.net/weixin_43296313/','您好,欢迎访问拒绝熬夜啊的博客');

2.在mysql数据库中创建身份证信息表(tb_idcard)

-- 判断数据表是否存在,存在则删除
drop table if exists tb_idcard;
 
-- 创建“身份证信息”数据表
create table if not exists tb_idcard
( 
	id int auto_increment primary key comment '身份证id',
	user_id int not null comment '用户编号',
	idcard_code varchar(45) comment '身份证号码'
) comment = '身份证信息表';
 
-- 添加数据
insert into tb_idcard(user_id,idcard_code) value(1,'123456789');

3.创建用户信息持久化类(userinfo.java)

@data
@allargsconstructor
@noargsconstructor
public class userinfo {
    private int userid; //用户编号
    private string useraccount; //用户账号
    private string userpassword; //用户密码
    private string blogurl; //博客地址
    private string remark; //备注
    private idcardinfo idcardinfo; //身份证信息
}

4.创建身份证信息持久化类(idcardinfo.java)

@data
@allargsconstructor
@noargsconstructor
public class idcardinfo {
    public int id; //身份证id
    public int userid; //用户编号
    public string idcardcode; //身份证号码
}

5.创建usermapper接口(用户信息mapper动态代理接口)

@repository
@mapper
public interface usermapper {
    /**
     * 获取用户信息和身份证信息
     * 一对一关联查询
     */
    @select("select * from tb_user where user_id = #{userid}")
    @results(id = "userandidcardresultmap", value = {
            @result(property = "userid", column = "user_id", javatype = integer.class, jdbctype = jdbctype.integer, id = true),
            @result(property = "useraccount", column = "user_account",javatype = string.class, jdbctype = jdbctype.varchar),
            @result(property = "userpassword", column = "user_password",javatype = string.class, jdbctype = jdbctype.varchar),
            @result(property = "blogurl", column = "blog_url",javatype = string.class, jdbctype = jdbctype.varchar),
            @result(property = "remark", column = "remark",javatype = string.class, jdbctype = jdbctype.varchar),
            @result(property = "idcardinfo",column = "user_id",
                    one = @one(select = "com.mye.hl07mybatis.api.mapper.usermapper.getidcardinfo", fetchtype = fetchtype.lazy))
    })
    userinfo getuserandidcardinfo(@param("userid")int userid);
 
    /**
     * 根据用户id,获取身份证信息
     */
    @select("select * from tb_idcard where user_id = #{userid}")
    @results(id = "idcardinforesultmap", value = {
            @result(property = "id", column = "id"),
            @result(property = "userid", column = "user_id"),
            @result(property = "idcardcode", column = "idcard_code")})
    idcardinfo getidcardinfo(@param("userid")int userid);
}

6.实现实体类和数据表的映射关系

在springboot启动类中加 @mapperscan(basepackages = “com.mye.hl07mybatis.api.mapper”) 注解。

@springbootapplication
@mapperscan(basepackages = "com.mye.hl07mybatis.api.mapper")
public class hl07mybatisapplication {

    public static void main(string[] args) {
        springapplication.run(hl07mybatisapplication.class, args);
    }
}

7.编写执行方法,获取用户信息和身份证信息(一对一关联查询)

@springboottest(classes = hl07mybatisapplication.class)
@runwith(springrunner.class)
public class hl07mybatisapplicationtests {

    @autowired
    private usermapper usermapper;

    /**
     * 获取用户信息和身份证信息
     * 一对一关联查询
     * @author pan_junbiao
     */
    @test
    public void getuserandidcardinfo() {
        //执行mapper代理对象的查询方法
        userinfo userinfo = usermapper.getuserandidcardinfo(1);
        //打印结果
        if(userinfo!=null) {
            system.out.println("用户编号:" + userinfo.getuserid());
            system.out.println("用户账号:" + userinfo.getuseraccount());
            system.out.println("用户密码:" + userinfo.getuserpassword());
            system.out.println("博客地址:" + userinfo.getblogurl());
            system.out.println("备注信息:" + userinfo.getremark());
            system.out.println("-----------------------------------------");

            //获取身份证信息
            idcardinfo idcardinfo = userinfo.getidcardinfo();
            if(idcardinfo!=null) {
                system.out.println("身份证id:" + idcardinfo.getid());
                system.out.println("用户编号:" + idcardinfo.getuserid());
                system.out.println("身份证号码:" + idcardinfo.getidcardcode());
            }
        }
    }
}

执行结果:

Mybatis使用@one和@Many实现一对一及一对多关联查询

三、使用@many注解实现一对多关联查询

需求:获取用户信息,同时获取一对多关联的权限列表

1.在mysql数据库创建权限信息表(tb_role)

-- 判断数据表是否存在,存在则删除
drop table if exists tb_role;
 
-- 创建“权限信息”数据表
create table if not exists tb_role
( 
	id int auto_increment primary key comment '权限id',
	user_id int not null comment '用户编号',
	role_name varchar(50) not null comment '权限名称'
) comment = '权限信息表';
 
insert into tb_role(user_id,role_name) values(1,'系统管理员'),(1,'新闻管理员'),(1,'广告管理员');

2.创建权限信息持久化类(roleinfo.java)

@data
@allargsconstructor
@noargsconstructor
public class roleinfo {
    private int id; //权限id
    private int userid; //用户编号
    private string rolename; //权限名称
}

3.修改用户信息持久化类(userinfo.java),添加权限列表的属性字段

@data
@allargsconstructor
@noargsconstructor
public class userinfo {
    private int userid; //用户编号
    private string useraccount; //用户账号
    private string userpassword; //用户密码
    private string blogurl; //博客地址
    private string remark; //备注
    private idcardinfo idcardinfo; //身份证信息
    private list<roleinfo> roleinfolist; //权限列表
}

4.编写用户信息mapper动态代理接口(usermapper.java)

/**
 * 获取用户信息和权限列表
 * 一对多关联查询
 * @author pan_junbiao
 */
@select("select * from tb_user where user_id = #{userid}")
@results(id = "userandrolesresultmap", value = {
        @result(property = "userid", column = "user_id", javatype = integer.class, jdbctype = jdbctype.integer, id = true),
        @result(property = "useraccount", column = "user_account",javatype = string.class, jdbctype = jdbctype.varchar),
        @result(property = "userpassword", column = "user_password",javatype = string.class, jdbctype = jdbctype.varchar),
        @result(property = "blogurl", column = "blog_url",javatype = string.class, jdbctype = jdbctype.varchar),
        @result(property = "remark", column = "remark",javatype = string.class, jdbctype = jdbctype.varchar),
        @result(property = "roleinfolist",column = "user_id", many = @many(select = "com.pjb.mapper.usermapper.getrolelist", fetchtype = fetchtype.lazy))
})
public userinfo getuserandrolesinfo(@param("userid")int userid);
 
/**
 * 根据用户id,获取权限列表
 * @author pan_junbiao
 */
@select("select * from tb_role where user_id = #{userid}")
@results(id = "roleinforesultmap", value = {
        @result(property = "id", column = "id"),
        @result(property = "userid", column = "user_id"),
        @result(property = "rolename", column = "role_name")})
public list<roleinfo> getrolelist(@param("userid")int userid);

5.编写执行方法,获取用户信息和权限列表(一对多关联查询)

/**
     * 获取用户信息和权限列表
     * 一对多关联查询
     * @author pan_junbiao
     */
    @test
    public void getuserandrolesinfo() {
        //执行mapper代理对象的查询方法
        userinfo userinfo = usermapper.getuserandrolesinfo(1);
        //打印结果
        if(userinfo!=null) {
            system.out.println("用户编号:" + userinfo.getuserid());
            system.out.println("用户账号:" + userinfo.getuseraccount());
            system.out.println("用户密码:" + userinfo.getuserpassword());
            system.out.println("博客地址:" + userinfo.getblogurl());
            system.out.println("备注信息:" + userinfo.getremark());
            system.out.println("-----------------------------------------");

            //获取权限列表
            list<roleinfo> roleinfolist = userinfo.getroleinfolist();
            if(roleinfolist!=null && roleinfolist.size()>0) {
                system.out.println("用户拥有的权限:");
                for (roleinfo roleinfo : roleinfolist) {
                    system.out.println(roleinfo.getrolename());
                }
            }
        }
    }

执行结果:

Mybatis使用@one和@Many实现一对一及一对多关联查询

四、fetchtype.lazy 和 fetchtype.eager的区别

fetchtype.lazy:懒加载,加载一个实体时,定义懒加载的属性不会马上从数据库中加载。

fetchtype.eager:急加载,加载一个实体时,定义急加载的属性会立即从数据库中加载。

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