Flutter sembast problem with updating values

I am learning by myself a thing or two about Flutter. Here the problem: i am using a simple sembast DB to store a key. I want to give the user the ability to change it. This is how the DB looks like:

{"version":1,"sembast":1}
{"key":"user_key","value":"random-chars"}

How to properly update the 'random-chars' string?

I am trying with put and update functions but my code is generating a new record instead of updating the existing one. Here the codes i have tried:

String dbPath = 'db.db';
DatabaseFactory dbFactory = databaseFactoryIo;

Future replaceKey(String k) async {
    Database db = await dbFactory.openDatabase(dbPath);
    var store = StoreRef.main();
    await store.record('user_key').put(db, k);
    //await store.update(db, k, finder: Finder(filter: Filter.byKey('user_key')));
  }

Solution

I am trying with put and update functions but my code is generating a new record instead of updating the existing one

I'm not sure what you mean by "generating a new record". My guess is that you are looking directly at the db file content. From an app point of view, the record should indeed get updated. Sembast use an append only format that get compacted at some point. This is explained here: https://github.com/tekartik/sembast.dart/blob/master/sembast/doc/storage_format.md