Fairway spec

Demos

Boad validation

Web view

Run

go run ./cmd/render -file examples/cart.cue -outdir .board/ -watch

go run ./cmd/tui -dir .board/
cd web && BOARD_DIR=../.board npm run dev

Using in Another Repo

Add dependency:

cue mod init your.module/name
cue mod get github.com/err0r500/event-modeling-dcb-spec@latest

Import schema:

package myboard

import "github.com/err0r500/event-modeling-dcb-spec/em"

em.#Board & {
    name: "MyDomain"
    // ...
}

Validation Rules

Board Structure

Rule	Description
Actor existence	Actors referenced in slices must exist in actors
Event definition	Emitted events must be defined in events
Tag definition	All tags in DCB queries must exist in tags

Change Slice (Command)

Rule	Description
Field source	Command fields must come from trigger (endpoint params/body or externalEvent), mapping, or computed
Field type	Types must match between source and command field
Emit field source	Event fields must come from command.fields, mapping, or computed
Emit field type	Types must match between source and event field
Path param consistency	Endpoint path params (e.g. {cartId}) must exist in params fields

View Slice (Query)

Rule	Description
Event ordering	Can only query events emitted by earlier change slices in flow
ReadModel field source	Fields must come from queried events, computed, or mapping
Computed event queried	Computed source event must be in query
Computed field exists	Computed fields must exist in source event
Mapping event queried	Mapping source event must be in query
Mapping field exists	Mapping field must exist in source event
Mapping type match	ReadModel field type must match event field type
Dotted path resolution	Dotted paths (e.g. "items.price") must resolve to actual fields (Go)
Dotted path type	Resolved field type must match event field type (Go)
Path param consistency	Endpoint path params (e.g. {cartId}) must exist in params fields
Scenario given in query	View scenario given events must be in query types

DCB Query

Rule	Description
Event has tags	Every event in query must have ALL required tags
Parameterized tag value	Tags with param require a value in queries (Go)

GWT Scenarios

Rule	Description
Command name match	Scenario when.name must match slice command name
Given event in query	Given events must be in command's query types
Then event in emits	Success scenario then.events must be in slice's emits
Event value types	Event field values must match field types

---

Future Improvements

Category	Check	Description
Structural	Non-empty emits	Change slice with empty emits is likely a mistake
Structural	Computed/mapping overlap	Same field shouldn't be both computed AND mapped
Type	Tag value type	Parameterized tag value should match tag.param type
Type	View endpoint response	Endpoint should reflect readModel (currently not linked)
Scenario	All emits tested	Every emitted event should appear in at least one success scenario
Scenario	Error scenario for queries	Commands with non-empty query should have error scenarios
DCB	Query not empty when needed	Command that emits to existing aggregate needs query to load state