The Order That Choreographs Itself
Nobody in Pacco approves an order - a vehicle reservation does. A tour of DevMentors' parcel-delivery estate, the domain it models, and the fifteen-part series it earns.
Series
The Order That Choreographs Itself
In reading order.
- 15 parts
- ≈ 96 min total
- 15 published
Three Ages of a Domain Model
Same framework, same four-project layout, three maturities - Parcels publishes from handlers, Orders raises events and maps them inline, Availability runs a full pipeline. The lineage made diffable.
The Reservation That Bumps You
Availability's Resource aggregate enforces one real business rule - a higher-priority reservation evicts yours and announces it. The invariant, the struct value object behind it, and the day-integer it becomes on disk.
One Event, Five Contracts
Every transition of Pacco's Order raises the same domain event - OrderStateChanged - and a mapper switches on aggregate status to mint five distinct integration events. A content-based router keyed on state, weighed honestly.
A Checkout With No Conductor
Pacco's flagship flow reconstructed from source - a vehicle is assigned, a reservation lands, an order approves itself, and when a VIP bumps the booking the cancellation ripples through three services with no process manager in sight.
Correlation by Natural Key
Availability's ResourceReserved event carries no order id, no correlation id, no saga id - just a resource and a date. Orders finds the right order anyway, by treating (vehicleId, deliveryDate) as the correlation key, and the expropriation flow shows exactly when that key stops being unique.
Rejected Events and How They Rot
Convey's IRejectedEvent gives Pacco an application-level negative acknowledgement - a rejected twin for every command. Reading the four exception-to-message mappers shows the pattern decaying in four different ways, from a failed reserve announced as a failed release to rejection classes nothing ever constructs.
The Parcel That Wouldn't Leave
Order.DeleteParcel raises a ParcelDeleted event and never removes the parcel from the set, while Parcels' cancel and delete handlers detach exactly one parcel of many. Two bounded contexts maintain the same association independently, both with bugs, and end up permanently disagreeing about a fact.
Same Fact, Two Names
Inside the Customers service a registration completes - and the rest of the estate hears that a customer was created. Three lines of EventMapper perform the best ubiquitous-language translation in Pacco, sitting on top of a lifecycle state machine with one guarded transition and four administrative jumps.
Three Ways to Borrow Another Service's Data
Four Pacco services need customer data and no two agree on how to get it - Orders and Parcels keep id-only replicas fed by events, Availability phones home mid-command, and Pricing pulls the full details document to count one number. One upstream, three consistency stances, five representations of the same entity.
The Outbox With Transactions Turned Off
Every Pacco service that enables Convey's Mongo outbox also sets disableTransactions to true - the aggregate write and the outbox write are separate operations, the pattern's one guarantee switched off in configuration. Meanwhile the inbox that would absorb the resulting duplicates sits beside three handlers that throw on them.
CQRS at the Transport Layer
In Pacco the CQRS split is not a diagram - it is wiring you can read. Every command arrives through two front doors, RabbitMQ subscription and controller-less HTTP dispatch, while queries ride HTTP only; commands assign their own ids in the constructor, and a marker attribute turns each service into its own runtime contract registry.
Optimistic Concurrency That Never Says No
Availability guards every save with a version-filtered ReplaceOneAsync - and discards the result, so a lost update is indistinguishable from a successful one and the integration event ships either way. Three folders away, Orders and Customers inherit the same AggregateRoot name with the versioning quietly deleted.
One Request, Four Services
AssignVehicleToOrder is the one command in Pacco that cannot finish alone - Orders calls Vehicles, then Pricing, and Pricing calls Customers, a synchronous enrichment chain on the write path of a messaging estate. At the end of it sits a deliberately bus-less calculator with a loyalty ladder, an unassigned Id and a discount logged in dollars.
Rich Rules, Demo-Grade Data
The series retrospective - Pacco's domain teaches real rules (state machines, priority expropriation, loyalty ladders, compensations) on top of cardboard data (bare-decimal prices, one vehicle per order, size-cube parcels, no payment, and a capacity check that ships in two halves nobody ever connects). What to steal, what to distrust, and what fourteen parts of source-reading add up to.