使用 Go-GORM 实现 YAML 到自引用 UUID 的转换

使用 Go-GORM 构建自引用 UUID 多对多关系时遇到问题。尽管尝试使用 uuid.uuid 类型，但无法正确解析 YAML 文件或在 Go-GORM 中识别关系。通过引入一个额外的间接级别，使用一个仅包含 UUID 的新相关活动类型，并为其实现 unmarshalyaml，最终解决了问题。该解决方案在 linked_activities 表中创建了正确的多对多关系。

我正在尝试从 yaml 文件创建自引用的 many2many。引用保存为 uuid，所以我尝试过：

type activity struct {
    id                uuid.uuid    `yaml:"id" gorm:"type:uuid;primarykey"`
    activitystreamid  uuid.uuid    `yaml:"stream" gorm:"type:uuid"`
    maturitylevelid   uuid.uuid    `yaml:"level" gorm:"type:uuid"`
    title             string       `yaml:"title"`
    benefit           string       `yaml:"benefit"`
    shortdescription  string       `yaml:"shortdescription"`
    longdescription   string       `yaml:"longdescription" gorm:"type:text"`
    results           stringarray  `yaml:"results" gorm:"type:text[]"`
    metrics           stringarray  `yaml:"metrics" gorm:"type:text[]"`
    costs             string       `yaml:"costs"`
    personnel         stringarray  `yaml:"personnel" gorm:"type:text[]"`
    notes             string       `yaml:"notes"`
    relatedactivities []*activities `yaml:"relatedactivities" gorm:"type:uuid;many2many:related_activities"`
    type              string       `yaml:"type"`
    questions         []question   `gorm:"type:uuid;many2many:activity_questions;"`
}

问题是，虽然这看起来像是 go-gorm 的正确用法，但它在 yaml 中无法正确解组：

2020/10/31 21:10:28 problem unmarshaling example.yml: yaml: unmarshal errors:
  line 47: cannot unmarshal !!str `e17d573...` into example.activity
exit status 1

当将 relatedactivities 切换为使用 uuid.uuid 时，yaml 工作正常，但在 go-gorm 中无法正确识别：

...
relatedactivities []*uuid.uuid `yaml:"relatedactivities" gorm:"type:uuid;many2many:related_activities"`
...

我在此示例中使用 sqlite：

2020/10/31 21:11:51 .../populateDB.go:60 row value misused
[0.063ms] [rows:0] INSERT INTO `activities` (`id`,`activity_stream_id`,`maturity_level_id`,`title`,`benefit`,`short_description`,`long_description`,`results`,`metrics`,`costs`,`personnel`,`notes`,`related_activities`,`type`,`questions`) VALUES ("a573c126-b3e3-45fb-a9d1-d94c8158cf60","1a7ad26d-9e48-411e-95a6-3be79e1b90ea","1cb6e197-ca82-45ec-a65b-0ecbdd784720","Enforce timely patch management","Clear view","Actively.....","Develop ...","{}","{}","","{}","",("93dff7be-5f95-4f8d-87d2-4f4261002508","2bf0e192-a904-444b-8a2f-38c33256e80a","0082a76b-1a37-44d9-ab04-43bd2168e13d"),"Activity",(NULL))
2020/10/31 21:11:51 row value misused
...

显然发生这种情况是因为自引用是 ("93dff7be-5f95-4f8d-87d2-4f4261002508","2bf0e192-a904-444b-8a2f-38c33256e80a","0082a76b-1a37-44d9-ab04 中的列表- 43bd2168e13d")，但未在新的 many2many 表中创建。

接下来我应该尝试什么？

解决方案

嗯，这就是我最终所做的：额外的间接级别。

没有指向 []*activity，而是添加了一个仅包含 uuid 的新 relatedactivity。

// activity
type activity struct {
    id                uuid.uuid         `yaml:"id" gorm:"type:uuid;primarykey"`
    activitystreamid  uuid.uuid         `yaml:"stream" gorm:"type:uuid"`
    maturitylevelid   uuid.uuid         `yaml:"level" gorm:"type:uuid"`
    title             string            `yaml:"title"`
    benefit           string            `yaml:"benefit"`
    shortdescription  string            `yaml:"shortdescription"`
    longdescription   string            `yaml:"longdescription" gorm:"type:text"`
    results           stringarray       `yaml:"results" gorm:"type:text[]"`
    metrics           stringarray       `yaml:"metrics" gorm:"type:text[]"`
    costs             string            `yaml:"costs"`
    personnel         stringarray       `yaml:"personnel" gorm:"type:text[]"`
    notes             string            `yaml:"notes"`
    relatedactivities []relatedactivity `yaml:"relatedactivities" gorm:"many2many:linked_activities"`
    type              string            `yaml:"type"`
    questions         []question        `gorm:"type:uuid;many2many:activity_questions;"`
}

type relatedactivity struct {
    id uuid.uuid `yaml:"id" gorm:"type:uuid"`
}

还为 relatedactivity 类型实现了 unmarshalyaml，如下所示：

// implements the unmarshaler interface of the yaml pkg.
func (r *relatedactivity) unmarshalyaml(unmarshal func(interface{}) error) error {
    var myuuid uuid.uuid
    err := unmarshal(&myuuid)
    if err != nil {
        return err
    }

    r.id = myuuid

    return nil
}

这在表 linked_activities 中创建了正确的多对多关系：

sqlite> select * from linked_activities ;
27cdd2a3-36a4-4e56-a426-32c7a78fcf4f|e17d5735-1090-4f65-a1fe-6040b56ad0b1
1cc77725-cb23-49f3-9447-7838668f6184|e17d5735-1090-4f65-a1fe-6040b56ad0b1
93dff7be-5f95-4f8d-87d2-4f4261002508|921ff24f-0b9f-4df9-a512-9aa2f8a4a570
93dff7be-5f95-4f8d-87d2-4f4261002508|b3b20a75-740c-4880-a21a-d9aa0c1298c7
d1cb54f1-ddd3-4324-8051-3df320fc0ff8|93dff7be-5f95-4f8d-87d2-4f4261002508
2bf0e192-a904-444b-8a2f-38c33256e80a|00000000-0000-0000-0000-000000000000
15d73a64-818c-4301-9504-c8d938ca2434|2bf0e192-a904-444b-8a2f-38c33256e80a
15d73a64-818c-4301-9504-c8d938ca2434|c1aef013-7df1-400c-bdd3-c660b609b7b2
15d73a64-818c-4301-9504-c8d938ca2434|05073fb1-30c7-4143-a12a-6ba74a44c580
d955a7b3-fbfc-4b6a-a5b3-27af9e01c377|11dd0c95-f891-4b6c-b850-a27f0557a9dd
d955a7b3-fbfc-4b6a-a5b3-27af9e01c377|281369f4-91da-4d4c-84b0-729e344e2c93
d955a7b3-fbfc-4b6a-a5b3-27af9e01c377|05a3e75c-6c65-4ae5-8a11-5cbf4295662b
f2a309b8-2fbc-46cf-b2f1-1c9cde20dc0a|5bcb5237-5a0f-4085-bb12-266c9ecfa84d
f2a309b8-2fbc-46cf-b2f1-1c9cde20dc0a|4f6a0679-6d08-40de-bcc7-75ea1af65679
f2a309b8-2fbc-46cf-b2f1-1c9cde20dc0a|a395d699-17b9-47b2-8d59-95738d716283
bcc960e8-35aa-4ad5-8a9d-39a272cbf6f1|4f6a0679-6d08-40de-bcc7-75ea1af65679

我认为这应该由 gorm 处理，但至少它适合我的情况。

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