Mobile local database, which one I chosen?

There are many ways to store databases for mobile.  I have the rules when choosing a mobile DB: Lightweight, Low memory, Fast, secure, and easy to use. I have used a few databases for mobile, in conclusion, I refer to using SQLite or Realm.

Both these databases are relational databases and designed for mobile.

If your application needs a simple database, SQLite is a good choice, it also supports transactions besides CRUD basic.

// SQL Lite
function getSettings(callBack) {
  db.transaction(function (txn) {
    txn.executeSql(
      'SELECT * FROM Settings',
      [],
      function (tx, res) {
        let settings = {};
        if (res.rows.length > 0) {
          const len = res.rows.length;
          for (let i = 0; i < len; i++) {
            const row = res.rows.item(i);
            if (row.datatype === 'bool') {
              settings[row.code] = row.value === 'true';
            } else {
              settings[row.code] = row.value;
            }
          }
        }
        callBack(settings);
      },
      handleErrorCB,
    );
  });
}

If your app needs need a database more complex, Realm is better than SQLite, Realm has a good engine to help us to work on native objects and always sync with the real DB, whatever you change it will sync with DB (changes in write method).

Realm is also faster than SQLite and more secure.

Realm provides Realm studio to connect with the DB to view, edit, and design…

The application can have a local database, and a remote database, It can be automatically synced with the remote DB.

// Realm
async function getSetting(): Promise<SettingModel> {
  const settings = realm.objects<SettingModel>(TABLE_NAME);
  if (settings.length === 0) {
    return getDefaultSetting();
  }
  return createSettingFromData(settings[0]);
}

async function saveSetting(settingInput: SettingModel): Promise<SettingModel> {
  if (settingInput.id === '') {
    settingInput.id = Guid.create().toString();
  }
  const settings = realm.objects<SettingModel>(TABLE_NAME);
  let setting: SettingModel;
  if (settings.length > 0) {
    setting = settings[0];
  }

  const result = realm.write(() => {
    if (!setting) {
      return realm.create(TABLE_NAME, settingInput, Realm.UpdateMode.Modified);
    } else {
      setting.companyName = settingInput.companyName;
      setting.taxPercent = settingInput.taxPercent;
      setting.isIncludeTax = settingInput.isIncludeTax;
      setting.phone = settingInput.phone;
      setting.address = settingInput.address;
      setting.currency = settingInput.currency;
      setting.language = settingInput.language;
      return setting;
    }
  });

  return createSettingFromData(result);
}

But Real files can not open concurrently by multiple threads, it is inconvenient in some cases. RealmObject is live objects, some time got issues when modifying objects.