Database queries function without network connectivity

When every data query requires a live network round-trip, users on flaky connections — subways, elevators, rural areas — get a blank or broken screen. Mobile network reliability is not a product assumption; it is a variable you must handle. ISO 25010:2011 reliability.fault-tolerance and recoverability both penalize apps that have no local query path. Beyond connectivity, local queries are also faster by orders of magnitude: a SQLite SELECT takes microseconds; a network call takes hundreds of milliseconds even on good connections. An offline query layer is the foundation for every other pattern in this bundle.

Add a local database layer using expo-sqlite or WatermelonDB, then route at least one primary data-loading function through it before hitting the network.

// npm install expo-sqlite
import * as SQLite from 'expo-sqlite';

const db = SQLite.openDatabase('app.db');

export const initDB = () =>
  new Promise<void>((resolve, reject) =>
    db.transaction(tx =>
      tx.executeSql(
        'CREATE TABLE IF NOT EXISTS items (id TEXT PRIMARY KEY, data TEXT, updated_at INTEGER);',
        [],
        () => resolve(),
        (_, err) => { reject(err); return false; }
      )
    )
  );

export const queryItems = (): Promise<unknown[]> =>
  new Promise((resolve, reject) =>
    db.transaction(tx =>
      tx.executeSql(
        'SELECT * FROM items ORDER BY updated_at DESC;',
        [],
        (_, result) => resolve(result.rows._array),
        (_, err) => { reject(err); return false; }
      )
    )
  );

On first launch, seed the local DB from the network. On subsequent launches, read from local first, then sync in the background via data-sync-on-reconnect.