Transition

Transition is a Golang state machine implementation.

it can be used standalone, but it integrates nicely with GORM models. When integrated with GORM, it will also store state change logs in the database automatically.

Usage

Enable Transition for your struct

Embed transition.Transition into your struct, it will enable the state machine feature for the struct:

import "github.com/qor/transition"

type Order struct {
  ID uint
  transition.Transition
}

Define States and Events

var OrderStateMachine = transition.New(&Order{})

// Define initial state
OrderStateMachine.Initial("draft")

// Define a State
OrderStateMachine.State("checkout")

// Define another State and what to do when entering and exiting that state.
OrderStateMachine.State("paid").Enter(func(order interface{}, tx *gorm.DB) error {
  // To get order object use 'order.(*Order)'
  // business logic here
  return
}).Exit(func(order interface{}, tx *gorm.DB) error {
  // business logic here
  return
})

// Define more States
OrderStateMachine.State("cancelled")
OrderStateMachine.State("paid_cancelled")


// Define an Event
OrderStateMachine.Event("checkout").To("checkout").From("draft")

// Define another event and what to do before and after performing the transition.
OrderStateMachine.Event("paid").To("paid").From("checkout").Before(func(order interface{}, tx *gorm.DB) error {
  // business logic here
  return nil
}).After(func(order interface{}, tx *gorm.DB) error {
  // business logic here
  return nil
})

// Different state transitions for one event
cancellEvent := OrderStateMachine.Event("cancel")
cancellEvent.To("cancelled").From("draft", "checkout")
cancellEvent.To("paid_cancelled").From("paid").After(func(order interface{}, tx *gorm.DB) error {
  // Refund
}})

Trigger an Event

// func (*StateMachine) Trigger(name string, value Stater, tx *gorm.DB, notes ...string) error
OrderStatemachine.Trigger("paid", &order, db, "charged offline by jinzhu")
// notes will be used to generate state change logs when works with GORM

// When using without GORM, just pass nil to the db, like
OrderStatemachine.Trigger("cancel", &order, nil)

OrderStatemachine.Trigger("cancel", &order, db)
// order's state will be changed to cancelled if current state is "draft"
// order's state will be changed to paid_cancelled if current state is "paid"

Get/Set State

var order Order

// Get Current State
order.GetState()

// Set State
order.SetState("finished") // this will only update order's state, won't save it into database

State change logs

When working with GORM, Transition will store all state change logs in the database. Use GetStateChangeLogs to get those logs.

// create the table used to store logs first
db.AutoMigrate(&transition.StateChangeLog{})

// get order's state change logs
var stateChangeLogs = transition.GetStateChangeLogs(&order, db)

// type StateChangeLog struct {
//   From       string  // from state
//   To         string  // to state
//   Note       string  // notes
// }

License

Released under the MIT License.