handleCommand

@delta-base/toolkit

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Function: handleCommand()

handleCommand<State, TEvent>(eventStore, streamId, handler, options): Promise<CommandHandlerResult<State, TEvent>>

Creates a command handler without Decider pattern

Steps:

1. Aggregate the stream to get current state
2. Run business logic using Handler function
3. Append events to stream
4. Return result with new state and events

Type Parameters

State

State

TEvent

TEvent extends Readonly<{ data: EventData; metadata?: PlatformEventMetadata; type: string; }> = Readonly<{ data: EventData; metadata?: PlatformEventMetadata; type: string; }>

Parameters

eventStore

EventStore

The event store instance

streamId

string

The stream identifier

handler

Handler<State, TEvent>

The handler function that processes state and returns events

options

CommandHandlerOptions<State, TEvent>

Command handler options including evolve, initialState, etc.

Returns

Promise<CommandHandlerResult<State, TEvent>>

Promise resolving to command handler result with new state and events

Example

const result = await handleCommand(
  eventStore,
  'user-123',
  (state) => [{ type: 'UserRegistered', data: { userId: '123' } }],
  {
    evolve: (state, event) => ({ ...state, registered: true }),
    initialState: () => ({ registered: false })
  }
);