Bank Account Example

The example/bank application is the absolute most minimal implementation of the flux framework.

It is designed to show you how the core pieces fit together in a single main.go file without any advanced project layout or network routing.

What it demonstrates

1. Domain Events: Defining basic structs like AccountCreated and MoneyDeposited.
2. The Aggregate Root: Embedding flux.AggregateRoot into a BankAccount struct.
3. The apply mutator: Changing the aggregate's internal balance exclusively through events.
4. Command Bus: Wiring up a basic command dispatcher.
5. In-Memory Storage: Using eventstore.New() and flux.NewAggregateRepository to save and load state locally.

Running the Example

Navigate to the directory and run it:

cd example/bank
go run main.go

Expected Output:

Loaded Account: Alice, Balance: $0
Loaded Account: Alice, Balance: $250

Source Code Highlight

The most important part of this example is the Aggregate definition. Notice how Deposit() enforces business invariants, but state mutation only happens inside apply()!

type BankAccount struct {
	flux.AggregateRoot[flux.Event]
	Owner   string
	Balance int
}

func (a *BankAccount) Deposit(amount int) error {
	if amount <= 0 {
		return errors.New("cannot deposit negative amount")
	}
	a.Changeset().Record(MoneyDeposited{Amount: amount})
	return nil
}

func (a *BankAccount) apply(event flux.Event) error {
	switch e := event.(type) {
	case AccountCreated:
		a.Owner = e.Owner
	case MoneyDeposited:
		a.Balance += e.Amount
	}
	return nil
}