# Persistence

Ndk comes with several database offerings. The simplest is the MemCacheManager which is an in-memory cache. This is useful for testing and small applications.

Available databases:

MemCacheManager
DbObjectBox
IsarCacheManager

If you want your own database, you need to implement the CacheManager interface. Contributions for more database implementations are welcome!

Its recommended to use the database only for ndk and spin up a secondary db for your own app data.

objectbox example
import 'package:ndk/ndk.dart';
import 'package:ndk_objectbox/ndk_objectbox.dart';

...

  DbObjectBox myObjectboxDb = DbObjectBox();
  await myObjectboxDb.dbRdy;
  final CacheManager db = myObjectboxDb;

  final ndkConfig = NdkConfig(
    cache: db,
    eventSigner: eventSigner,
    eventVerifier: eventVerifier,
  );

  final ndk = Ndk(ndkConfig);

Tip: A simple way to keep your own entities is to use a factory method to convert ndk events to your own entities.

tip: conversion - glue code
/// from camelus.app - nostr_note_model.dart
class NostrNoteModel extends NostrNote {
  ...

  // convert from ndk event to your own entity with additional fields
  factory NostrNoteModel.fromNDKEvent(Nip01Event nip01event) {
    final myTags =
        nip01event.tags.map((tag) => NostrTagModel.fromJson(tag)).toList();

    return NostrNoteModel(
      id: nip01event.id,
      pubkey: nip01event.pubKey,
      created_at: nip01event.createdAt,
      kind: nip01event.kind,
      content: nip01event.content,
      sig: nip01event.sig,
      tags: myTags,
      sig_valid: nip01event.validSig,
      sources: nip01event.sources,
    );
  }
  ...
}