FactsCallback

FactsCallback<TTo> = (args, currentFacts) => object

Defined in: packages/@livestore/common/dist/schema/EventDef/facts.d.ts:86

Callback function that defines how an event interacts with the facts system. Called during event processing to determine fact constraints.

Type Parameters

TTo

TTo

Parameters

args

TTo

currentFacts

EventDefFacts

Returns

modify

modify: object

modify.set

set: Iterable<EventDefFactInput>

Facts to set (create or update).

modify.unset

unset: Iterable<EventDefFactInput>

Facts to unset (remove).

require

require: Iterable<EventDefFactInput>

Facts that must exist with specific values for this event to be valid.

Example

const factsCallback: FactsCallback<{ id: string }> = (args, currentFacts) => ({
  modify: {
    set: [`item:${args.id}`],  // Create/update this fact
    unset: [],                  // No facts to remove
  },
  require: currentFacts.has('initialized') ? [] : ['initialized'],
})