BankAccountES

Bank Account (Event Sourcing) — Critter Stack Sample

Domain Reference

Inspired by: andreschaffer/event-sourcing-cqrs-examples (Java)

A minimalistic bank domain demonstrating Marten event sourcing with Wolverine aggregate handlers. Not a code port — built from scratch using the Java project's domain concepts.

Domain

• Client — enroll, update profile (event-sourced)
• Account — open, deposit, withdraw (event-sourced, with balance guard)
• Transaction History — inline projection built from deposit/withdrawal events

Patterns Demonstrated

Aggregate Handler Workflow ([AggregateHandler])

Deposit and withdrawal operations use Wolverine's [AggregateHandler] attribute. Wolverine loads the Account aggregate from the event stream, passes it to the handler, appends the returned event, and commits — all in one transaction.

[WolverinePost("/api/accounts/{accountId}/deposits")]
[AggregateHandler]
public static FundsDeposited Post(DepositFunds command, Account account)
{
    var newBalance = account.Balance + command.Amount;
    return new FundsDeposited(command.AccountId, command.Amount, newBalance);
}

Validate Against Aggregate State

Withdrawal validates against the loaded aggregate's balance using a separate Validate method (Railway Programming pattern):

public static ProblemDetails Validate(WithdrawFunds command, Account account)
{
    if (account.Balance < command.Amount)
        return new ProblemDetails { Detail = "Insufficient funds", Status = 400 };
    return WolverineContinue.NoProblems;
}

Inline Snapshot Projections

Account and Client aggregates use SnapshotLifecycle.Inline — the snapshot document is always up-to-date after each event append.

Single-Stream Read Model Projection

AccountTransactionsProjection builds a transaction history per account from deposit/withdrawal events, registered as an inline projection.

Entity Loading with Batch Query

OpenAccount uses [Entity] to load the Client by ClientId — verifying the client exists before opening an account.

Running

Requires PostgreSQL.

dotnet run

Swagger UI at /swagger.

API

Method	Route	Description
POST	/api/clients	Enroll a new client
PUT	/api/clients/{clientId}	Update client profile
GET	/api/clients/{id}	Get client
POST	/api/accounts	Open account for a client
GET	/api/accounts/{id}	Get account
GET	/api/clients/{clientId}/accounts	Get all accounts for a client
POST	/api/accounts/{accountId}/deposits	Deposit funds
POST	/api/accounts/{accountId}/withdrawals	Withdraw funds
GET	/api/accounts/{accountId}/transactions	Transaction history