Custom Persistence

When you want to load and save Store data in unusual or custom ways, you can used the createCustomPersister function to do so in any way you wish.

As well as providing a reference to the Store to persist, you must provide functions that handle how to fetch, write, and listen to, the persistence layer.

Functions To Implement

To build a custom Persister, you should provide four functions:

• getPersisted, an asynchronous function which will fetch content from the persistence layer (or null or undefined if not present).
• setPersisted, an asynchronous function which will send content to the persistence layer.
• addPersisterListener, a function that will register a listener listener on underlying changes to the persistence layer. You can return a listening handle that will be provided again when delPersisterListener is called.
• delPersisterListener, a function that will unregister the listener from the underlying changes to the persistence layer. It receives whatever was returned from your addPersisterListener implementation. @returns A reference to the new Persister object.

Note that the first two functions are asynchronous and must return promises. The latter two are synchronous and should return void (i.e. should not return a value at all).

This API changed in v4.0. Any custom persisters created on previous versions should be upgraded. Most notably, the setPersisted function parameter is provided with a getContent function to get the content from the Store itself, rather than being passed pre-serialized JSON. It also receives information about the changes made during a transaction. The getPersisted function must return the content (or nothing) rather than JSON. startListeningToPersisted has been renamed addPersisterListener, and stopListeningToPersisted has been renamed delPersisterListener.

This example creates a custom Persister object that persists the Store to a local string called storeJson and which would automatically load by polling for changes every second:

import {createCustomPersister} from 'tinybase/persisters';
import {createStore} from 'tinybase';

const store = createStore().setTables({pets: {fido: {species: 'dog'}}});
let storeJson;
let interval;

const persister = createCustomPersister(
  store,
  async () => {
    try {
      return JSON.parse(storeJson);
    } catch {}
  },
  async (getContent) => (storeJson = JSON.stringify(getContent())),
  (listener) => (interval = setInterval(listener, 1000)),
  () => clearInterval(interval),
);

await persister.save();
console.log(storeJson);
// -> '[{"pets":{"fido":{"species":"dog"}}},{}]'

storeJson = '[{"pets":{"fido":{"species":"dog","color":"brown"}}},{}]';
await persister.load();

console.log(store.getTables());
// -> {pets: {fido: {species: 'dog', color: 'brown'}}}

persister.destroy();

Note that the other creation functions (such as the createSessionPersister function and createFilePersister function, for example) all use this function under the covers. See those implementations for ideas on how to implement your own Persister types.