如何在 Gorm 中留下连接子查询计数
Posted
技术标签:
【中文标题】如何在 Gorm 中留下连接子查询计数【英文标题】：How to left join subquery count in Gorm 【发布时间】：2021-12-19 21:03:32 【问题描述】：我希望我的 Gorm 查询返回正确的 version_count。我的 Gorm 查询返回 0 version_count，而我的 mysql 查询返回 version_count。
我有下面的 MySQL 查询，用于将子查询计数连接到最终查询结果中。
我有这个用于我的 Gorm 查询：
subQuery := models.DB.Select("services.id as services_id, COUNT(versions.service_id) as version_count").Group("services.id").Preload("Versions").Table("Services").SubQuery()
models.DB.Preload("Versions").Find(&services).Count(&count).Limit(limit).Offset(offset).
Joins("LEFT JOIN (?) as version_counts ON version_counts.services_id = s.id", subQuery)
去结构
type Service struct
ID uint `json:"id" gorm:"primary_key"`
Name string `json:"name"`
Description string `json:"description"`
Versions []Version `json:"versions"`
VersionCount int `json:"version_count"`
CreatedAt string `json:"created_at"`
type Version struct
ID uint `json:"id" gorm:"primary_key"`
Version string `json:"name"`
ServiceID string `json:"service_id"`
CreatedAt string `json:"created_at"`
UpdatedAt string `json:"updated_at"`
有我的查询表。
mysql> select * from services;
+----+---------------------+---------------------+------------+--------+-------------+
| id | created_at | updated_at | deleted_at | name | description |
+----+---------------------+---------------------+------------+--------+-------------+
| 1 | 2021-11-05 21:16:25 | 2021-11-05 21:16:25 | NULL | John | New York |
| 2 | 2021-11-05 21:16:25 | 2021-11-05 21:16:25 | NULL | Martin | Los Angeles |
+----+---------------------+---------------------+------------+--------+-------------+
2 rows in set (0.02 sec)
mysql> select * from versions;
+----+---------------------+---------------------+------------+------------+---------+
| id | created_at | updated_at | deleted_at | service_id | version |
+----+---------------------+---------------------+------------+------------+---------+
| 1 | 2021-11-05 21:16:25 | 2021-11-05 21:16:25 | NULL | 1 | 1.0.0 |
| 2 | 2021-11-05 21:16:25 | 2021-11-05 21:16:25 | NULL | 1 | 1.0.1 |
| 3 | 2021-11-05 21:16:25 | 2021-11-05 21:16:25 | NULL | 1 | 1.0.2 |
| 4 | 2021-11-05 21:16:25 | 2021-11-05 21:16:25 | NULL | 2 | 1.0.0 |
| 5 | 2021-11-05 21:16:25 | 2021-11-05 21:16:25 | NULL | 2 | 1.0.1 |
| 6 | 2021-11-05 21:16:25 | 2021-11-05 21:16:25 | NULL | 2 | 1.0.2 |
| 7 | 2021-11-05 21:16:25 | 2021-11-05 21:16:25 | NULL | 2 | 1.0.3 |
+----+---------------------+---------------------+------------+------------+---------+
7 rows in set (0.01 sec)
mysql> select * from services s join versions v on v.service_id = s.id left join ( select s.id services_id, count(v.service_id) as version_count from services s join versions v on v.service_id = s.id group by s.id) version_counts ON version_counts.services_id = s.id;
+----+---------------------+---------------------+------------+--------+-------------+----+---------------------+---------------------+------------+------------+---------+-------------+---------------+
| id | created_at | updated_at | deleted_at | name | description | id | created_at | updated_at | deleted_at | service_id | version | services_id | version_count |
+----+---------------------+---------------------+------------+--------+-------------+----+---------------------+---------------------+------------+------------+---------+-------------+---------------+
| 1 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | John | New York | 1 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | 1 | 1.0.0 | 1 | 3 |
| 1 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | John | New York | 2 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | 1 | 1.0.1 | 1 | 3 |
| 1 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | John | New York | 3 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | 1 | 1.0.2 | 1 | 3 |
| 2 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | Martin | Los Angeles | 4 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | 2 | 1.0.0 | 2 | 4 |
| 2 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | Martin | Los Angeles | 5 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | 2 | 1.0.1 | 2 | 4 |
| 2 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | Martin | Los Angeles | 6 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | 2 | 1.0.2 | 2 | 4 |
| 2 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | Martin | Los Angeles | 7 | 2021-11-05 20:20:09 | 2021-11-05 20:20:09 | NULL | 2 | 1.0.3 | 2 | 4 |
+----+---------------------+---------------------+------------+--------+-------------+----+---------------------+---------------------+------------+------------+---------+-------------+---------------+
7 rows in set (0.01 sec)
【问题讨论】：
【参考方案1】：我能够使用适当的 version_count 加载响应。
带有原始查询的 Gorm（更短更容易）
models.DB.Preload("Versions").Table("Services s").
Select("*").
Joins("left join (select s.id services_id, count(v.service_id) as version_count " +
"from services s " +
"join versions v on v.service_id = s.id " +
"group by s.id) version_counts " +
"ON version_counts.services_id = s.id").
Find(&services)
Gorm 查询（更复杂）
subQuery := models.DB.Debug().Table("Services s").
Select("s.id services_id, count(v.service_id) as version_count").
Joins("JOIN versions v ON v.service_id = s.id").Group("s.id").SubQuery()
models.DB.Debug().Preload("Versions").Table("Services s").
Select("*").
Joins("left join " +
"(" +
"?" +
") version_counts " +
"ON version_counts.services_id = s.id", subQuery).
Find(&services).Count(&count).Limit(limit).Offset(offset)
【讨论】：
以上是关于如何在 Gorm 中留下连接子查询计数的主要内容，如果未能解决你的问题，请参考以下文章