编写插件
原文：https://gorm.io/docs/write_plugins.html
回调 Callbacks
GORM itself is powered by Callbacks, it has callbacks for Create, Query, Update, Delete, Row, Raw, you could fully customize GORM with them as you want
GORM 本身由 Callbacks 提供支持，它具有用于 Create、Query、Update、Delete、Row、Raw 的回调，您可以根据需要完全自定义 GORM。
Callbacks are registered into the global *gorm.DB, not the session-level, if you require *gorm.DB with different callbacks, you need to initialize another *gorm.DB
回调被注册到全局的 *gorm.DB 中，而不是会话级别。如果您需要具有不同回调的 *gorm.DB，则需要初始化另一个 *gorm.DB。
注册回调 Register Callback
Register a callback into callbacks
将回调注册到回调中
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| func cropImage(db *gorm.DB) {
if db.Statement.Schema != nil {
// crop image fields and upload them to CDN, dummy code
for _, field := range db.Statement.Schema.Fields {
switch db.Statement.ReflectValue.Kind() {
case reflect.Slice, reflect.Array:
for i := 0; i < db.Statement.ReflectValue.Len(); i++ {
// Get value from field
if fieldValue, isZero := field.ValueOf(db.Statement.Context, db.Statement.ReflectValue.Index(i)); !isZero {
if crop, ok := fieldValue.(CropInterface); ok {
crop.Crop()
}
}
}
case reflect.Struct:
// Get value from field
if fieldValue, isZero := field.ValueOf(db.Statement.Context, db.Statement.ReflectValue); !isZero {
if crop, ok := fieldValue.(CropInterface); ok {
crop.Crop()
}
}
// Set value to field
err := field.Set(db.Statement.Context, db.Statement.ReflectValue, "newValue")
}
}
// All fields for current model
db.Statement.Schema.Fields
// All primary key fields for current model
db.Statement.Schema.PrimaryFields
// Prioritized primary key field: field with DB name `id` or the first defined primary key
db.Statement.Schema.PrioritizedPrimaryField
// All relationships for current model
db.Statement.Schema.Relationships
// Find field with field name or db name
field := db.Statement.Schema.LookUpField("Name")
// processing
}
}
db.Callback().Create().Register("crop_image", cropImage)
// register a callback for Create process
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删除回调 Delete Callback
Delete a callback from callbacks
从回调中删除回调
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| db.Callback().Create().Remove("gorm:create")
// delete callback `gorm:create` from Create callbacks
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替换回调 Replace Callback
Replace a callback having the same name with the new one
用新函数替换具有相同名称的回调
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| db.Callback().Create().Replace("gorm:create", newCreateFunction)
// replace callback `gorm:create` with new function `newCreateFunction` for Create process
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按顺序注册回调 Register Callback with orders
Register callbacks with orders
按顺序注册回调
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| // before gorm:create
db.Callback().Create().Before("gorm:create").Register("update_created_at", updateCreated)
// after gorm:create
db.Callback().Create().After("gorm:create").Register("update_created_at", updateCreated)
// after gorm:query
db.Callback().Query().After("gorm:query").Register("my_plugin:after_query", afterQuery)
// after gorm:delete
db.Callback().Delete().After("gorm:delete").Register("my_plugin:after_delete", afterDelete)
// before gorm:update
db.Callback().Update().Before("gorm:update").Register("my_plugin:before_update", beforeUpdate)
// before gorm:create and after gorm:before_create
db.Callback().Create().Before("gorm:create").After("gorm:before_create").Register("my_plugin:before_create", beforeCreate)
// before any other callbacks
db.Callback().Create().Before("*").Register("update_created_at", updateCreated)
// after any other callbacks
db.Callback().Create().After("*").Register("update_created_at", updateCreated)
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定义的回调 Defined Callbacks
GORM has defined some callbacks to power current GORM features, check them out before starting your plugins
GORM 有一些预定义的回调来增强当前 GORM 功能，在开始插件之前请先查看它们。
插件 Plugin
GORM provides a Use method to register plugins, the plugin needs to implement the Plugin interface
GORM 提供了一个 Use 方法来注册插件，插件需要实现 Plugin 接口。
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| type Plugin interface {
Name() string
Initialize(*gorm.DB) error
}
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The Initialize method will be invoked when registering the plugin into GORM first time, and GORM will save the registered plugins, access them like:
Initialize 方法将在将插件注册到 GORM 时首次调用，GORM 将保存已注册的插件，如下所示：
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| db.Config.Plugins[pluginName]
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Checkout Prometheus as example
以 Prometheus为例