Cqrs on Brian Faust

CQRS Starts When Reads Need a Different Model

Mon, 01 May 2023 00:00:00 +0000

An order-details page needs customer name, payment status, shipment progress, line totals, tax labels, and the latest support case. The write model needs to protect payment, cancellation, and fulfilment invariants.

Trying to make one Eloquent graph serve both jobs creates a familiar mess: relationships exist for screen composition, write methods expose persistence concerns, and every request loads a different subset of a model that is never quite complete.

That tension can justify different read and write models. It does not automatically justify two databases, an event store, a command bus, or eventual consistency. CQRS is the model split; the infrastructure is a separate set of decisions.

A Queued Command Changes the Contract

Sat, 01 Apr 2023 00:00:00 +0000

Send the same payment-capture request through two Laravel routes.

The synchronous route returns 204 after the provider has created charge ch_001 and the order records that reference. When the provider returns 503, the HTTP request returns 500 and the order remains unpaid.

The queued route returns 202 while the order is still unpaid and the provider ledger is empty. Its response contains an operation URL. Cancel the order before a worker starts and that operation later becomes refused; the provider is never called.

A Command Bus Must Pay for Its Indirection

Wed, 01 Mar 2023 00:00:00 +0000

Four Laravel routes handle two commands in the reproducible fixture . Two routes inject typed handlers. Two inject Laravel’s dispatcher. All four return 204, and both call graphs leave the same SQLite rows behind.

Then one line disappears from the dispatcher’s handler map. The bus route still resolves its controller, constructs CancelOrder, and enters the pipeline. It returns 500 without selecting a handler. The direct controller has no equivalent registry entry to lose because its constructor already names DirectCancelOrderHandler.

A Valid Command Can Still Be Refused

Wed, 01 Feb 2023 00:00:00 +0000

Send this cancellation request to two orders:

{
 "reason": "customer_request"
}

The placed order returns 204 and becomes cancelled. The shipped order returns 409 and remains shipped. Both requests pass the same Laravel Form Request.

Change the reason to unknown and the result is different again: Laravel returns 422 before the controller constructs a command. Three requests crossed two different decision boundaries. Calling one result “valid” and the others “invalid” hides the part of the system which made each decision.