Models

Models are pre-built methods for subscribing to computed state from the EventStore.

INFO

Models do not fetch any events from relays, they only subscribe to the events that are already in the event store.

Using models

The eventStore.model method can be used to create a model and returns a rxjs observable that can be subscribed to.

import { TimelineModel } from "applesauce-core/models";

// The first argument is the model constructor and the remaining are passed to the model
const observable = eventStore.model(TimelineModel, { kinds: [1] });

// start the query by subscribing to it
observable.subscribe((events) => {
  console.log(events);
});

// adding events to the event store will update the timeline query
eventStore.add({kind: 1, content: 'new note', ...})

Performance

Models with similar arguments are cached in the event store and reused for performance reasons. This can help with multiple UI components subscribing to the same model.

import { ProfileModel } from "applesauce-core/models";

// Create the first model
const first = eventStore.model(ProfileModel, { pubkey: "pubkey" });

// Create the second model
const second = eventStore.model(ProfileModel, { pubkey: "pubkey" });

// Both will be the same observable
console.log(first === second); // true

Prebuilt Models

There are some common prebuilt models that come with applesauce-core

• ProfileModel subscribes to a single pubkey's profile (kind 0)
• TimelineModel subscribes to a sorted array of events that match filters
• RepliesQuery subscribes to all NIP-10 and NIP-22 replies to an event

And there are a lot more in the docs

Custom Models

A custom model is simply a function that returns a Model function.

import { Model } from "applesauce-core";

function CustomModel(arg: string): Model<string> {
  return (eventStore) =>
    new Observable((observer) => {
      // observable code here
      observer.next("testing");
    });
}

As an example here is a custom model that will parse a NIP-78 app event that contains JSON

import { map } from "rxjs/operators";
import { Model } from "applesauce-core";

/** A model that gets JSON from a app data event */
function AppSettingsModel<T>(pubkey: string): Model<T> {
  return (eventStore) =>
    eventStore.replaceable(30078, pubkey, "app-settings").pipe(
      map((event) => {
        if (!event) return undefined;
        return JSON.parse(event.content) as T;
      }),
    );
}

// Create the model and subscribe to it
const sub = eventStore
  .model(AppSettingsModel, "3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d")
  .subscribe((json) => {
    // json will either be undefined or { theme: string }
    if (json) console.log("updated data", json);
  });

// Add an event to the event store to trigger the model
eventStore.add({
  kind: 30078,
  content: '{"theme": "dark"}',
  // rest of event
});