EventVersions

The older shapes of one event, so that events stored long ago still reach projections and view models in today’s shape. The log is never rewritten: old payloads are upcast as they are read.

const AccountOpenedV1 = Schema.Struct({ owner: Schema.String })

const Account = Aggregate.make<State>()({
  name: "account",
  events: AccountEvent,
  initial,
  projection,
  versions: {
    AccountOpened: EventVersions.from(AccountOpenedV1).next(
      AccountEvent.cases.AccountOpened,
      ({ owner }) => ({ owner, currency: "CHF" })
    )
  }
})

The first schema is version 1, the shape events had before the history was declared, and every next adds a version. The last one must be the event’s current schema, which is what new events are written with.

Interfaces

EventVersions

Defined in: src/EventVersions.ts:44

Type Parameters

Schemas

Schemas extends ReadonlyArray<VersionSchema>

Latest

Latest

Properties

~latest?

readonly optional ~latest?: Latest

Defined in: src/EventVersions.ts:50

The type of the last version, which an aggregate checks against its event.

schemas

readonly schemas: Schemas

Defined in: src/EventVersions.ts:46

Oldest first: schemas[0] is version 1.

upcasts

readonly upcasts: readonly ((previous) => unknown)[]

Defined in: src/EventVersions.ts:48

upcasts[i] turns version i + 1 into version i + 2.

Methods

next()

next<Next>(schema, upcast): EventVersions<readonly [Schemas, Next], Next["Type"]>

Defined in: src/EventVersions.ts:52

Adds a version, with the function that turns the previous one into it.

Type Parameters

Next

Next extends VersionSchema

Parameters

schema

Next

upcast

(previous) => Untagged<Next["Type"]>

Returns

EventVersions<readonly [Schemas, Next], Next["Type"]>

Type Aliases

Any

Any<Latest> = EventVersions<ReadonlyArray<VersionSchema>, Latest>

Defined in: src/EventVersions.ts:59

Any history whose last version is Latest.

Type Parameters

Latest

Latest = any

---

SchemaAt

SchemaAt<H, V> = H extends EventVersions<infer Schemas, any> ? [never, ...Schemas][V] extends infer S ? S : never : never

Defined in: src/EventVersions.ts:62

The schema of one version, or never when the history has no such version.

Type Parameters

H

H extends Any

V

V extends number

---

Untagged

Untagged<T> = T extends object ? Omit<T, "_tag"> : T

Defined in: src/EventVersions.ts:38

What an upcast returns: the next version, without the _tag the event’s name already gives.

Type Parameters

T

T

---

VersionSchema

VersionSchema = Schema.Top & object

Defined in: src/EventVersions.ts:32

A schema that decodes and encodes without services, as stored payloads need.

Type Declaration

DecodingServices

readonly DecodingServices: never

EncodingServices

readonly EncodingServices: never

Functions

current()

current(versions): number

Defined in: src/EventVersions.ts:80

The version new events of this kind are written with.

Parameters

versions

Any<any> | undefined

Returns

number

---

decoders()

decoders(tag, versions): readonly Decoder<unknown, never>[]

Defined in: src/EventVersions.ts:90

Builds one decoder per old version, each going all the way to the current one. The chains are composed once with Schema.decodeTo, so reading an old event costs one decode however many versions it is behind.

decoders[v - 1] decodes a JSON payload stored at version v. The current version has none, as the aggregate’s own schema reads it.

Parameters

tag

string

versions

Any

Returns

readonly Decoder<unknown, never>[]

---

from()

from<V1>(schema): EventVersions<readonly [V1], V1["Type"]>

Defined in: src/EventVersions.ts:76

Starts a history at version 1.

Type Parameters

V1

V1 extends VersionSchema

Parameters

schema

V1

Returns

EventVersions<readonly [V1], V1["Type"]>