stalagmite
v0.0.10
Published
Event sourcing library that helps you building event sourced aggregates.
Downloads
9
Maintainers
Readme
Stalagmite
Stalagmite is a library that helps you building event sourced aggregates.
Installation:
npm install stalagmite
Documentation:
Access documentation here with examples
Example:
In this example we will create a simple aggregate for a counter. Find the complete counter example here
buildAggregate()
import { buildAggregate, Aggregate, AggregateState } from 'stalagmite';
export interface Counter extends Aggregate<CounterState, CounterEvents> {
init(counterId: string, initialCount: number): Outcome;
count(number: number): Outcome;
reset(): Outcome;
}
export interface CounterState extends AggregateState {
id: string;
count: number;
}
function counterEventResolver( // It's this function that mutate the state when applying an event.
state: CounterState,
event: CounterEvents,
): Outcome {
/*...*/
}
const commandId = 'command-id'; // The command you are building the aggregate for.
const aggregate = buildAggregate(commandId, initialState, eventResolver, {
snapshotEvery: 2, // This options will generate snapshots every 2 events added
});
// Expose your business methods and expose aggregate methods.
return {
init: () => {
/*...*/
},
count: () => {
/*...*/
},
reset: () => {
/*...*/
},
...aggregate,
};
To see an eventResolver example click here
Aggregate interface:
// Aggregate interface
aggregate.apply(events: Event | Event[]): ApplyEventOutcome; // Apply an event to the aggregate.
aggregate.addEvent(events: E): Outcome; // Add and apply a new event to the aggregate.
aggregate.getUncommmitedEvents(): E[]; // Returns new events created not commited yet.
aggregate.eventsCommited(): void; // Call this function when you have saved those events in your event store. It clear the uncommited events array.
aggregate.getSequence(): number; // Returns aggregate sequence.
aggregate.state(): S; // Returns a deep copy of the current state.
aggregate.snapshot(): S; // Create an aggregate snapshot and return it.
aggregate.getSnapshot(): S[]; // Get all snapshots created.
aggregate.snapshotsCommited(): void; // Empty the list of snapshots.