Refactor: Data Persistence

[seanwu1105]

We need levels of data persistence:

• Low level
  • SQL or noSQL DB
  • To store on devices
  • Interface
    • Reactive could be better
      • Reactive should NOT fail outside ngZone
    • Easy to change DB
    • Use a global (singleton?) to register document or table name to check naming conflicts in runtime
• Adapters
  • Converter between high and low levels
• High level
  • Nested JavaScript object complying standard "Proof" API (protocol)
  • To display or data interchange

[seanwu1105]

The low level for data persistence can be achieved with the Filesystem plugin from Capacitor. Each table is a big JSON file to store tuples. We also need a mutex lock to make sure each insertion or deletion on the same table is atomic. Furthermore, the codes for data persistence requires fully covered tests.

[seanwu1105]

Quoted from Slack message:

找個穩定且有在積極維護的替代方案來儲存檔案，但是這件事情需要至少半個 sprint，而且需要多方嘗試與實做試試看來比較，上次有跟 @james 討論過 RxDB 等等替代方案。目前最快的 workaround 是直接 catch 掉所有 Capacitor.Filesystem.deleteFile() 產生的錯誤訊息。但是這個解決方法很爛，而且只會讓未來越來越難 debug。

[seanwu1105]

#227 has implemented a reliable solution to #181 (comment).