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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 JSON from the persistence layer (or null or undefined if not present).
  • setPersisted, an asynchronous function which will send JSON to the persistence layer.
  • startListeningToPersisted, a function that will register a didChange listener on underlying changes to the persistence layer.
  • stopListeningToPersisted, a function that will unregister the listener from the underlying changes to the persistence layer.

Note that the first two functions are synchronous and must return promises. The latter two are synchronous and should return void.

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:

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

const persister = createCustomPersister(
  store,
  async () => storeJson,
  async (json) => (storeJson = json),
  (didChange) => (interval = setInterval(didChange, 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.