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Gorm Development

Architecture

The most notable component of Gorm isgorm.DB, which hold database connection. It could be initialized like this:

db, err := gorm.Open("postgres", "user=gorm dbname=gorm sslmode=disable")

Gorm has chainable API, gorm.DB is the bridge of chains, it save related information and pass it to the next chain.

Lets use below code to explain how it works:

db.Where("name = ?", "jinzhu").Find(&users)

// equivalent code
newdb := db.Where("name =?", "jinzhu")
newdb.Find(&user)

newdb is db's clone, in addition, it contains search conditions from the Where method. Find is a query method, it creates a Scope instance, and pass it as argument to query callbacks.

There are four kinds of callbacks corresponds to sql's CURD: create callbacks, update callbacks, query callbacks, delete callbacks.

Callbacks

Register a new callback

func updateCreated(scope *Scope) {
    if scope.HasColumn("Created") {
        scope.SetColumn("Created", NowFunc())
    }
}

db.Callback().Create().Register("update_created_at", updateCreated)
// register a callback for Create process

Delete an existing callback

db.Callback().Create().Remove("gorm:create")
// delete callback `gorm:create` from Create callbacks

Replace an existing callback

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

Register callback orders

db.Callback().Create().Before("gorm:create").Register("update_created_at", updateCreated)
db.Callback().Create().After("gorm:create").Register("update_created_at", updateCreated)
db.Callback().Query().After("gorm:query").Register("my_plugin:after_query", afterQuery)
db.Callback().Delete().After("gorm:delete").Register("my_plugin:after_delete", afterDelete)
db.Callback().Update().Before("gorm:update").Register("my_plugin:before_update", beforeUpdate)
db.Callback().Create().Before("gorm:create").After("gorm:before_create").Register("my_plugin:before_create", beforeCreate)

Callback API

Gorm is powered by callbacks, so you could refer below links to learn how to write callbacks

View https://github.com/jinzhu/gorm/blob/master/scope.go for all available API

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