声明模型

原文：https://gorm.io/docs/models.html

Models are normal structs with basic Go types, pointers/alias of them or custom types implementing Scanner and Valuer interfaces

​ 模型是具有基本Go类型的普通结构体，或者是它们的指针/别名，或者是实现了Scanner和Valuer接口的自定义类型。

For Example:

​ 例如：

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type User struct {
  ID           uint
  Name         string
  Email        *string
  Age          uint8
  Birthday     *time.Time
  MemberNumber sql.NullString
  ActivatedAt  sql.NullTime
  CreatedAt    time.Time
  UpdatedAt    time.Time
}

约定 Conventions

GORM prefers convention over configuration. By default, GORM uses ID as primary key, pluralizes struct name to snake_cases as table name, snake_case as column name, and uses CreatedAt, UpdatedAt to track creating/updating time

​ GORM 倾向于约定优于配置。默认情况下，GORM使用ID作为主键，将结构体名称转换为snake_cases作为表名，snake_case作为列名，并使用CreatedAt、UpdatedAt来追踪创建/更新时间。

If you follow the conventions adopted by GORM, you’ll need to write very little configuration/code. If convention doesn’t match your requirements, GORM allows you to configure them

​ 如果您遵循GORM采用的约定，您只需要编写很少的配置/代码。如果约定不符合您的要求，GORM允许您进行配置。

gorm.Model

GORM defined a gorm.Model struct, which includes fields ID, CreatedAt, UpdatedAt, DeletedAt

​ GORM定义了一个gorm.Model结构体，其中包含字段ID、CreatedAt、UpdatedAt、DeletedAt。

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// gorm.Model 的定义 gorm.Model definition
type Model struct {
  ID        uint           `gorm:"primaryKey"`
  CreatedAt time.Time
  UpdatedAt time.Time
  DeletedAt gorm.DeletedAt `gorm:"index"`
}

You can embed it into your struct to include those fields, refer Embedded Struct

​ 您可以将其嵌入到您的结构体中以包含这些字段，请参阅嵌入式结构体。

高级功能 Advanced

字段级权限控制 Field-Level Permission

Exported fields have all permissions when doing CRUD with GORM, and GORM allows you to change the field-level permission with tag, so you can make a field to be read-only, write-only, create-only, update-only or ignored

​ 导出的字段在进行GORM CRUD操作时具有所有权限，并且GORM允许您使用标签更改字段级权限，因此您可以使一个字段只读、只写、只创建、只更新或被忽略。

NOTE ignored fields won’t be created when using GORM Migrator to create table

注意：在使用GORM Migrator创建表时，被忽略的字段将不会被创建。

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type User struct {
  Name string `gorm:"<-:create"` // 允许读和创建 allow read and create
  Name string `gorm:"<-:update"` // 允许读和更新 allow read and update
  Name string `gorm:"<-"`        // 允许读和写（创建和更新） allow read and write (create and update)
  Name string `gorm:"<-:false"`  // 允许读，禁止写 allow read, disable write permission
  Name string `gorm:"->"`        // 只读（除非有自定义配置，否则禁止写） readonly (disable write permission unless it configured)
  Name string `gorm:"->;<-:create"` // 允许读和写 allow read and create
  Name string `gorm:"->:false;<-:create"` // 仅创建（禁止从 db 读） createonly (disabled read from db)
  Name string `gorm:"-"`            // 通过 struct 读写会忽略该字段 ignore this field when write and read with struct
  Name string `gorm:"-:all"`        // 通过 struct 读写、迁移会忽略该字段 ignore this field when write, read and migrate with struct
  Name string `gorm:"-:migration"`  // 通过 struct 迁移会忽略该字段 ignore this field when migrate with struct
}

创建/更新时间追踪 Time/Unix (Milli/Nano) 秒 Creating/Updating Time/Unix (Milli/Nano) Seconds Tracking

GORM use CreatedAt, UpdatedAt to track creating/updating time by convention, and GORM will set the current time when creating/updating if the fields are defined

​ GORM使用CreatedAt和UpdatedAt按照约定来追踪创建/更新时间，如果这些字段被定义了，GORM会在创建/更新时设置当前时间。

To use fields with a different name, you can configure those fields with tag autoCreateTime, autoUpdateTime

​ 如果你想使用不同名称的字段，你可以使用标签autoCreateTime和autoUpdateTime来配置这些字段。

If you prefer to save UNIX (milli/nano) seconds instead of time, you can simply change the field’s data type from time.Time to int

​ 如果你更喜欢保存UNIX（毫秒/纳秒）而不是时间，你可以直接将字段的数据类型从time.Time更改为int。

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type User struct {
  CreatedAt time.Time // 在创建时，如果该字段值为零值，则使用当前时间填充 Set to current time if it is zero on creating
  UpdatedAt int       // 在创建时该字段值为零值或者在更新时，使用当前时间戳秒数填充 Set to current unix seconds on updating or if it is zero on creating
  Updated   int64 `gorm:"autoUpdateTime:nano"` // 使用时间戳纳秒数填充更新时间 Use unix nano seconds as updating time
  Updated   int64 `gorm:"autoUpdateTime:milli"`// 使用时间戳毫秒数填充更新时间 Use unix milli seconds as updating time
  Created   int64 `gorm:"autoCreateTime"`      // 使用时间戳秒数填充创建时间 Use unix seconds as creating time
}

嵌入式结构体 Embedded Struct

For anonymous fields, GORM will include its fields into its parent struct, for example:

​ 对于匿名字段，GORM会将其字段包含到其父结构体中，例如：

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type User struct {
  gorm.Model
  Name string
}
// 等效于 equals
type User struct {
  ID        uint           `gorm:"primaryKey"`
  CreatedAt time.Time
  UpdatedAt time.Time
  DeletedAt gorm.DeletedAt `gorm:"index"`
  Name string
}

For a normal struct field, you can embed it with the tag embedded, for example:

​ 对于普通结构体字段，你可以通过使用embedded标签将其嵌入，例如：

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type Author struct {
  Name  string
  Email string
}

type Blog struct {
  ID      int
  Author  Author `gorm:"embedded"`
  Upvotes int32
}
// 等效于 equals
type Blog struct {
  ID    int64
  Name  string
  Email string
  Upvotes  int32
}

And you can use tag embeddedPrefix to add prefix to embedded fields’ db name, for example:

​ 你还可以使用embeddedPrefix标签为嵌入式字段的数据库名称添加前缀，例如：

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type Blog struct {
  ID      int
  Author  Author `gorm:"embedded;embeddedPrefix:author_"`
  Upvotes int32
}
// 等效于 equals
type Blog struct {
  ID          int64
  AuthorName  string
  AuthorEmail string
  Upvotes     int32
}

字段标签 Fields Tags

Tags are optional to use when declaring models, GORM supports the following tags:

​ 声明模型时使用标签是可选的，GORM支持以下标签：

Tags are case insensitive, however camelCase is preferred.

​ 标签不区分大小写，但是camelCase更受欢迎。

关联标签 Associations Tags

GORM allows configure foreign keys, constraints, many2many table through tags for Associations, check out the Associations section for details

​ GORM允许通过关联标签配置外键、约束和多对多表。有关详细信息，请参阅关联部分。