Update summary on shipped state

[tonypizzicato]

• Fix transitions between stock item states (e.g.decrease onHand count on Shipped)
• Introduce Shipped state for consistency
• Implement transactions proxy*
• Run summary update in transaction
• Wrap all existing transactions in a wrapper

Transactions proxy

Transactions proxy are implemented as a wrapper over gorm.DB

type Transaction struct {
	db      *gorm.DB
	wrapped bool
	Error   error
}

func NewTransaction(db *gorm.DB) *Transaction {
	_, inTxn := db.CommonDB().(*sql.Tx)

	return &Transaction{db, inTxn, nil}
}

func (txn *Transaction) runTransaction(methodName string, whenTxn bool) *Transaction {
	if txn.wrapped {
		return txn
	}

	if _, isTxn := txn.db.CommonDB().(*sql.Tx); isTxn == whenTxn {
		methodValue := reflect.ValueOf(txn.db).MethodByName(methodName)
		if !methodValue.IsValid() {
			panic(fmt.Sprintf("Can't call method %s of Transaction", methodName))
		}

		result := methodValue.Call([]reflect.Value{})

		txn.db = result[0].Interface().(*gorm.DB)
		txn.Error = txn.db.Error
	}

	return txn
}

Transactions is used in repos and knows when it is a repo-itself transaction (created with *sql.DB instance) or when it is already started transaction (instance of *sql.Tx). So it just proxies calls to *gorm.DB when transaction is not started and does nothing when transaction already begun.

Usage

txn := transaction.NewTransaction(repository.db).Begin()

In case when transaction was not started (repository.db is a regular db connection) it just proxies calls to *gorm.DB instance
When repo was instantiated with transaction (means transaction is managed outside repo)

	txn := service.db.Begin()
	shipmentRepo := repositories.NewShipmentRepository(txn)
        ...

	if err := txn.Commit().Error; err != nil {
		txn.Rollback()
		return nil, err
	}

calls to transaction methods in repo itself do nothing.

Running services with outer-managed transactions

To use a service in a service that already started transaction (e.g. https://github.com/FoxComm/highlander/blob/master/middlewarehouse/services/shipment_service.go#L72)
WithTransaction(txn *gorm.DB) IInventoryService method for such services was implemented

Usage

	txn := service.db.Begin()
        ...
	if err := service.inventoryService.WithTransaction(txn).ReserveItems(shipment.OrderRefNum); err != nil {
		txn.Rollback()
		return nil, err
	}

WithTransaction method return a copy of a service with txn *gorm.DB field set to passed transaction.
The same approach was used for repos.

func (service *inventoryService) getUnitRepo() repositories.IStockItemUnitRepository {
	if service.txn == nil {
		return service.unitRepo
	}

	return service.unitRepo.WithTransaction(service.txn)
}

In this case it service runs under outer-managed transaction, it gets a copy of a repo with transaction instead old *gorm.DB instace - service.unitRepo.WithTransaction(service.txn)

Using transaction proxy and WithTransaction approach together

In order to make transactions passing to work this two approaches should be used together.
But, in case of using transaction proxies without WithTransaction (means repos would always have own db instance instead one with started transaction) it would take no effect on code running and repo would start it's own transaction every time as it does right now.
But, in case of using WithTransaction methods without transactions proxy would lead to can't start transaction errors from gorm

[tonypizzicato]

Stock items status update in mwh fixes

[jmataya]

A couple small comments, otherwise this looks good!

[jmataya]

Hmm... thinking about the signature of this method - why do we pass the DB in from the outside, rather than use repository.db? And if we shouldn't be using any property from repository, why is this a member method on IShipmentRepository?

[jmataya]

Do we want to panic here or return an error?

[tonypizzicato]

this case is an error in the code, so i think it's better to fail asap with a panic

[jmataya]

I can buy that logic.

[jmataya]

Really like you pulling this into this service! 👍

[jmataya]

Talked through my concerns 1:1 with @tonypizzicato. These changes look good to me!