Gorm: What's the difference between "unique_index" and "unique"?

[fanybook]

一个是创建表时建索引?
一个是插入记录时的验证?

"unique_index" 和 "unique" 区别能否说一下

------------------------------验证结果--------------------------------
环境：mysql
方式：使用自动迁移生成的表
代码：

    TestUnique1     string      `gorm:"size:255;unique"`
    TestUnique2     string      `gorm:"size:255;unique_index"`

结果：只是索引名字的格式不同，多了uix_user2_ 前缀
test_unique1
uix_user2_test_unique2

[fanybook]

还有，在 gorm.Model 里，ID 是 uint
uint的实际位数和系统有关吧，以mysql举例
32位系统创建出来的字段是 int
32位系统创建出来的字段是 bigint?

这个我去验证一下

------------------------------验证结果--------------------------------
方式：使用自动迁移生成的表
验证：gorm.Model
结果：
3个时间戳字段全部位于最前方
uint 在64位win10的mysql里，生成了int型

[fanybook]

type User2 struct {
     Name         string
     Age          sql.NullInt64
     Birthday     *time.Time
     Email        string  `gorm:"type:varchar(100);unique_index"`
     Role         string  `gorm:"size:255"` // set field size to 255
     MemberNumber *string `gorm:"unique;not null"` // set member number to unique and not null
     Num          int     `gorm:"AUTO_INCREMENT"` // set num to auto incrementable
     Address      string  `gorm:"index:addr"` // create index with name `addr` for address
     IgnoreMe     int     `gorm:"-"` // ignore this field
     CreatedAt       time.Time
     UpdatedAt       time.Time
     DeletedAt       *time.Time
}

这段官方示例中，类型有指针型，这个不影响迁移，但是有什么区别？

使用上有区别吗

[fanybook]

如果我想为mysql的单个字段指定字符集

可以这样吗？

Comment         string  `gorm:"set utf8mb4"`

------------------------------验证结果--------------------------------
方式：使用自动迁移生成的表
结果：不起作用，新的comment 还是 utf8

[ermik]

unique means "has to be unique value", it's an equivalent of setting a UNIQUE constraint on a database table field.
unique_index means "index database on this value, which is unique", it's an equivalent of creating a unique index in the database — you can specify a name of such index and use the annotation with the same name on multiple struct fields:

// just an exampe
type Example struct {
    // two people can have the same name
    Name string `gorm:"primary_key;unique_index:exampleindex"`
    // but usernames have to be unique
    Username string `gorm:"unique;"`
    // colors can be repeating too
    FavoriteColor string `gorm:"unique_index:exampleindex"` 
    // But combinations of User + FavoriteColor have to be UNIQUE
}

[fanybook]

@ermik In MySQL, both via unique_index?

    TestUnique1     string      `gorm:"size:255;unique"`
    TestUnique2     string      `gorm:"size:255;unique_index"`

result：both created unique index, test2 have more prefix than test1
test_unique1
uix_user2_test_unique2

[ermik]

The default unique index creation for UNIQUE field is a ?bug?. I don't know if it's MySQL creating index for UNIQUE fields by default, or if it is gorm doing it.

It won't make your database slower...

To decide which option to use — think of the data you have and the _constraints_ you place on it as in example above.

[fanybook]

@ermik How to change a field's charset to utf8mb4?

gorm:"set utf8mb4" can't work

[cjun714]

DeletedAt *time.Time

In some cases if you want to set nil to a column(for example: end_time), you should define (EndTime * time.Time) in struct.

[ermik]

@fanybook try calling db.Set("gorm:table_options", "charset=utf8mb4")

[ermik]

@cjun714 you can define your own Model struct and embed it on your types.

[fanybook]

db.Set("gorm:table_options", "charset=utf8mb4") can set all varchar and text fields to utf8mb4

set utf8mb4 Only work on a single field

[github-actions[bot]]

This issue will be automatically closed because it is marked as GORM V1 issue, we have released the public testing GORM V2 release and its documents https://v2.gorm.io/docs/ already, the testing release has been used in some production services for a while, and going to release the final version in following weeks, we are still actively collecting feedback before it, please open a new issue for any suggestion or problem, thank you

Also check out https://github.com/go-gorm/gorm/wiki/GORM-V2-Release-Note-Draft for how to use the public testing version and its changelog