Mybatis中表关系查询结果集映射
文章目录
- 前言
- 1. 实体类设计
-
- 1.1 用户表
- 1.2 地址表
- 1.3 博客表
- 1.4 粉丝互关表
- 2.插入数据
- 3.表关联查询
-
- 3.1 一对一关系
- 3.2 一对多关系
- 3.3 多对多关系
前言
resultMap 元素是 MyBatis 中最重要最强大的元素。它可以让你从 90% 的 JDBC ResultSets 数据提取代码中解放出来，并在一些情形下允许你进行一些 JDBC 不支持的操作。实际上，在为一些比如连接的复杂语句编写映射代码的时候，一份 resultMap 能够代替实现同等功能的数千行代码。ResultMap 的设计思想是，对简单的语句做到零配置，对于复杂一点的语句，只需要描述语句之间的关系就行了。
ER实体关系：
- 一对一
- 一对多
- 多对多
1. 实体类设计
1.1 用户表
建表sql:
CREATE TABLE `User` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`name` varchar(100) DEFAULT NULL,
`age` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='用户表';
java实体类:
public class User implements Serializable {
private static final long serialVersionUID = 741077730204987800L;
private Long id;
private String name;
private Integer age;
}
1.2 地址表
建表的sql
CREATE TABLE `Address` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`user_id` bigint(20) DEFAULT NULL,
`province` varchar(100) DEFAULT NULL,
`city` varchar(100) DEFAULT NULL,
`county` varchar(100) DEFAULT NULL,
`detail` varchar(100) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='地址表';
java代码：
public class Address implements Serializable {
private static final long serialVersionUID = 960792204085182238L;
private Long id;
private Long userId;
private String province;
private String city;
private String county;
private String detail;
}
1.3 博客表
建表的sql
CREATE TABLE `Blogs` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`user_id` bigint(20) DEFAULT NULL,
`title` varchar(100) DEFAULT NULL,
`content` varchar(100) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
java实体类：
public class Blogs implements Serializable {
private static final long serialVersionUID = -82344806309770256L;
private Long id;
private Long userId;
private String title;
private String content;
}
1.4 粉丝互关表
建表的sql
-- test.Fans definition
CREATE TABLE `Fans` (
`id` varchar(100) DEFAULT NULL,
`user_id` bigint(20) DEFAULT NULL,
`fan_id` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='粉丝互关表';
实体类
public class Fans implements Serializable {
private static final long serialVersionUID = -76540062746539253L;
private String id;
private Long userId;
private String fanId;
}
2.插入数据
INSERT INTO `User`(id, name, age)VALUES(11, 'elite', 20);
INSERT INTO `User`(id, name, age)VALUES(12, 'bob', 19);
INSERT INTO `User`(id, name, age)VALUES(13, 'johon', 22);
INSERT INTO `User`(id, name, age)VALUES(14, 'smith', 21);
INSERT INTO `User`(id, name, age)VALUES(15, 'jackon', 20);
INSERT INTO Address(id, user_id, province, city, county, detail)VALUES(1, 11, 'bj', 'xx', 'xx', '北京西路');
INSERT INTO Address(id, user_id, province, city, county, detail)VALUES(2, 12, 'sh', 'xx', 'xx', '上海路');
INSERT INTO Address(id, user_id, province, city, county, detail)VALUES(3, 13, 'sz', 'xx', 'xx', '深圳南山路');
INSERT INTO Address(id, user_id, province, city, county, detail)VALUES(4, 14, 'gz', 'xx', 'xx', '广州路');
INSERT INTO Address(id, user_id, province, city, county, detail)VALUES(5, 15, 'hz', 'xx', 'xx', '杭州');
INSERT INTO Blogs(id, user_id, title, content)VALUES(1, 11, 'java', 'java数据类型...');
INSERT INTO Blogs(id, user_id, title, content)VALUES(2, 11, 'python', '大数据开发..');
INSERT INTO Blogs(id, user_id, title, content)VALUES(3, 11, 'c#', '桌面应用开发...');
INSERT INTO Fans(id, user_id, fan_id)VALUES(1, 11, 12);
INSERT INTO Fans(id, user_id, fan_id)VALUES(2, 11, 13);
INSERT INTO Fans(id, user_id, fan_id)VALUES(3, 12, 11);
INSERT INTO Fans(id, user_id, fan_id)VALUES(4, 12, 14);
INSERT INTO Fans(id, user_id, fan_id)VALUES(5, 12, 15);
3.表关联查询
3.1 一对一关系
表user和address是一对一的关系，可以直接定义一个dto来接收数据。
定义数据传输对象：
public class UADTO {
private Long id;
private String name;
private Integer age;
private String province;
private String city;
private String county;
private String detail;
}
定义resultmap结果集以及查询
<resultMap type="com.elite.mybatis.dto.UADTO" id="UAMap">
<result property="id" column="id" jdbcType="INTEGER"/>
<result property="name" column="name" jdbcType="VARCHAR"/>
<result property="age" column="age" jdbcType="INTEGER"/>
<result property="userId" column="user_id" jdbcType="INTEGER"/>
<result property="province" column="province" jdbcType="VARCHAR"/>
<result property="city" column="city" jdbcType="VARCHAR"/>
<result property="county" column="county" jdbcType="VARCHAR"/>
<result property="detail" column="detail" jdbcType="VARCHAR"/>
resultMap>
<sql id="uasql">
select
u.id,
u.name,
u.age,
a.province,
a.city,
a.county,
a.detail
from
User u,
Address a
where
u.id = a.user_id
sql>
<select id="getUAInfo" resultMap="UAMap">
<include refid="uasql">include>
select>
测试：
/**
* 测试一对一关系的查询
*/
@Test
public void testOne2One(){
CollectionMapper c = sqlSession.getMapper(CollectionMapper.class);
List<UADTO> uadtoList = c.getUAInfo();
uadtoList.forEach(uadto -> {
System.out.println(uadto.toString());
});
}
3.2 一对多关系
用户和发表的博客ER关系属于一对多关系。
定义传输的DTO对象
/**
* 用户表和博客发布的记录
*/
public class UBDTO {
private Long id;
private String name;
private Integer age;
private List<Blogs> blogs;
}
定义结果集
<resultMap id="UBMap" type="com.elite.mybatis.dto.UBDTO">
<id property="id" column="id" jdbcType="INTEGER"/>
<result property="name" column="name" jdbcType="VARCHAR"/>
<result property="age" column="age" jdbcType="INTEGER"/>
<collection property="blogs" ofType="com.elite.mybatis.entity.Blogs">
<id property="id" column="id" jdbcType="INTEGER"/>
<id property="userId" column="user_id" jdbcType="INTEGER"/>
<result property="title" column="title" jdbcType="VARCHAR"/>
<result property="content" column="content" jdbcType="VARCHAR"/>
collection>
resultMap>
<sql id="ubsql">
select
u.id,
u.name,
u.age,
b.id,
b.user_id,
b.title,
b.content
from
User u inner join Blogs b on (u.id = b.user_id)
sql>
<select id="getUBInfo" resultMap="UBMap">
<include refid="ubsql">include>
select>
测试
/**
* 测试一对多关系的查询
*/
@Test
public void testOne2Multi(){
CollectionMapper c = sqlSession.getMapper(CollectionMapper.class);
List<UBDTO> ubInfo = c.getUBInfo();
ubInfo.forEach(ubdto -> {
System.out.println(ubdto.toString());
});
}
3.3 多对多关系
用户表和粉丝表之间关系
定义dto
/**
* 粉丝互关表
*/
public class UFDTO {
private Long id;
private String name;
private Integer age;
private List<User> fans;
}
定义查询的结果集
<resultMap id="UFMap" type="com.elite.mybatis.dto.UFDTO">
<id property="id" column="id" jdbcType="INTEGER"/>
<result property="name" column="name" jdbcType="VARCHAR"/>
<result property="age" column="age" jdbcType="INTEGER"/>
<collection property="fans" ofType="com.elite.mybatis.entity.User">
<id property="id" column="id" jdbcType="INTEGER"/>
<result property="name" column="name" jdbcType="VARCHAR"/>
<result property="age" column="age" jdbcType="INTEGER"/>
collection>
resultMap>
<sql id="ufsql">
select
u.id,
u.name,
u.age,
f1.id,
f1.name,
f1.age
from
User u,
Fans f,
User f1
where
u.id = f.user_id
and f.fan_id = f1.id
sql>
<select id="getUFInfo" resultMap="UFMap">
<include refid="ufsql">include>
select>
测试
/**
* 测试多对多关系的查询
*/
@Test
public void testMulti2Multi(){
CollectionMapper c = sqlSession.getMapper(CollectionMapper.class);
List<UFDTO> ufdtoList = c.getUFInfo();
ufdtoList.forEach(ufdto -> {
System.out.println(ufdto.toString());
});
}
