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一对一关联查询
- 创建一个实体类
package com.touchspring.annualparty.base.entity;
import java.util.Date;
public class Chat {
private String id;
private String userId;
private String content;
private Date createAt;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
。。。。。。略 自行补足
或在类名前添加 @Data 注解可省略getter 和 setter
}
- 创建Dto类
package com.touchspring.annualparty.base.dto;
import com.touchspring.annualparty.base.entity.User;
import java.util.Date;
public class ChatDto {
private String id;
private String userId;
private String content;
private Date createAt;
/**
* 用户信息 一对一关联查询的对象
*/
private User user;
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
}
- 编写XML文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.touchspring.annualparty.base.dao.ChatDao">
<resultMap id="BaseResultMap" type="com.touchspring.annualparty.base.entity.Chat">
<id column="id" property="id"/>
<result column="user_id" property="userId"/>
<result column="content" property="content"/>
<result column="create_at" property="createAt"/>
</resultMap>
<resultMap id="BaseDtoResultMap" type="com.touchspring.annualparty.base.dto.ChatDto">
<id column="id" property="id"/>
<result column="user_id" property="userId"/>
<result column="content" property="content"/>
<result column="create_at" property="createAt"/>
<association property="user" javaType="com.touchspring.annualparty.base.entity.User">
<result column="firstName" property="firstName"/>
<result column="lastName" property="lastName"/>
<result column="photo" property="photo"/>
</association>
</resultMap>
<select id="findAllChats" resultMap="BaseDtoResultMap">
SELECT c.*,u.first_name AS firstNmae, u.last_name AS lastName,u.photo AS photo
FROM chat c LEFT JOIN user u
ON c.user_id = u.id
</select>
</mapper>
| property | 映射到列结果的字段或属性。对应实体中setter()的参数 |
| column | 数据库中的列名,或者是列的别名。一般情况下，这和 传递给 resultSet.getString(columnName) 方法的参数一样。 |
一对一关联 association 中使用 JavaType 返回项目实体类 一对多collection关联查询中的使用 ofType 返回项目实体类
结果集如下：
"comments": [
{
"id": "3",
"userId": "10051002",
"topic": "他",
"content": "信标",
"createAt": "2018-12-18 09:41",
"user": {
"id": null,
"lastName": "1",
"firstName": "1",
"title": null,
"function": null,
"department": null,
"country": null,
"telephone": null,
"photo": "2",
"password": null,
"email": null,
"userGroupId": null,
"color": null,
"passportId": null,
"visa": null,
"arrivalFlight": null,
"hotelCheckInAt": null,
"hotelCheckOutAt": null,
"clothingSize": null,
"foodRestriction": null,
"createAt": null
}
}
]一对多关联查询
- 实体类和Dto类创建基本一致，Dto中稍有不同 一对一为实体对象，一对多为List<Object>对象
public class EngineeringDto {
/**
* ID
*/
private String id;
/**
* 名称
*/
private String name;
/**
* 创建时间
*/
private Date createAt;
/**
* 更新时间
*/
private Date updateAt;
/**
* 分包商
*/
private List<Subcontractor> subcontractors;
}- xml文件如下
<mapper namespace="com.touchspring.isite.base.dao.EngineeringDao">
<resultMap id="BaseResultMap" type="com.touchspring.isite.base.entity.Engineering">
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="createAt" property="createAt"/>
<result column="updateAt" property="updateAt"/>
</resultMap>
<resultMap id="BaseResultMapDto" type="com.touchspring.isite.base.dto.EngineeringDto">
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="createAt" property="createAt"/>
<result column="updateAt" property="updateAt"/>
<result column="projectId" property="projectId"/>
<collection property="subcontractors" ofType="com.touchspring.isite.base.entity.Subcontractor">
<result column="subcontractorId" property="id"/>
<result column="subcontractorName" property="name"/>
</collection>
</resultMap>
<select id="findListInProject" resultMap="BaseResultMapDto">
SELECT e.*,s.id subcontractorId,s.name subcontractorName FROM engineering e
LEFT JOIN engineering_subcontractor es
ON e.id = es.engineering_id
LEFT JOIN subcontractor s
ON s.id = es.subcontractor_id
WHERE
<if test="id != null and id != ''">
es.project_id = #{id}
</if>
</select>
</mapper>
- 结果如下
"engineering": [
{
"id": "111",
"name": "机电消防安装",
"createAt": null,
"updateAt": null,
"subcontractors": [
{
"id": "1041156821873725440",
"name": "上海建工集团股份有限公司",
"phone": null,
"subType": null,
"subManager": null,
"subAddress": null,
"parentId": null,
"createAt": null,
"updateAt": null,
"children": null,
"totalCount": null,
"image": null
},
{
"id": "1041199607712976896",
"name": "上海威盟斯建筑工程有限公司",
"phone": null,
"subType": null,
"subManager": null,
"subAddress": null,
"parentId": null,
"createAt": null,
"updateAt": null,
"children": null,
"totalCount": null,
"image": null
}
],
"projectId": null,
"engAndSubRelationIdArr": null
}
]