Write Plugins


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

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

Register Callback

Register a callback into callbacks

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 {
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 {

// Set value to field
err := field.Set(db.Statement.Context, db.Statement.ReflectValue, "newValue")

// All fields for current model

// All primary key fields for current model

// Prioritized primary key field: field with DB name `id` or the first defined primary key

// All relationships for current model

// 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

Delete Callback

Delete a callback from callbacks

// delete callback `gorm:create` from Create callbacks

Replace Callback

Replace a callback having the same name with the new one

db.Callback().Create().Replace("gorm:create", newCreateFunction)
// replace callback `gorm:create` with new function `newCreateFunction` for Create process

Register Callback with orders

Register callbacks with orders

// 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)

Defined Callbacks

GORM has defined some callbacks to power current GORM features, check them out before starting your plugins


GORM provides a Use method to register plugins, the plugin needs to implement the Plugin interface

type Plugin interface {
Name() string
Initialize(*gorm.DB) error

The Initialize method will be invoked when registering the plugin into GORM first time, and GORM will save the registered plugins, access them like:


Checkout Prometheus as example

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