Upgrade database by using onUpgrade callback properly - database

Question

I'm fetching data from a website (JSON) and save it in a database. This works well. However, I want to upgrade the database with a new version number every time the data fetched from the internet changes. For that, I think the best way is to drop the table, upgrade the database number version and recreate the table before filling it with the new data (at least there is a way to insert only new records and update only the old ones that have changed).
I saw that it could be done with the onUpgrade callback on a Database from the sqflite plugin.
So, I created an Helper with an init() method that open the database.
However, I don't understand when the onUpgrade callback is called. Indeed, in this code below, version is always at 1.
I would like to have a method that init the DB and :
creates it if it does not exists OR
open the current version if no number version is specified (something like that) OR
upgrade to a new version by auto-incrementing the version number (by calling database.upgrade() for example).
Do you think this is possible in a unique method or do I need to split that in two methods ? If yes, what's the point of the onUpgrade callback ?
class DBHelper {
// Private constructor
DBHelper._privateConstructor();
// Get an instance of DBHelper
static final DBHelper _dbHelper = DBHelper._privateConstructor();
// Getter to get the instance of the DBHelper
factory DBHelper() => _dbHelper;
static Database _database;
Future<Database> get database async {
if (_database != null) return _database;
// lazily instantiate the db the first time it is accessed
_database = await init();
return _database;
}
Future<Database> init() async {
print("DBHelper: init database");
// Get a location using path_provider
String path = await getDBPath();
// I THINK ALL HAPPENS HERE
return await openDatabase(path, version: 1, onCreate: _onCreate, onUpgrade: _onUpgrade);
}
void _onCreate(Database db, int version) async {
print("DBHelper: _onCreate called");
// When creating the db, create the table
_createTable();
}
void _onUpgrade(Database db, int oldVersion, int newVersion) async{
print("DBHelper: _onUpgrade called");
try {
await db.transaction((Transaction txn) async {
await txn.execute("DROP TABLE TABLE_NAME");
});
} catch (e) {
print("Error : " + e.toString());
}
_createTable();
}
void _createTable() async {
Database db = await database;
try {
await db.transaction((Transaction txn) async {
await txn.execute("CREATE TABLE TABLE_NAME ("
"TABLE_ID INTEGER PRIMARY KEY AUTOINCREMENT,"
"TABLE_INT INTEGER,"
"TABLE_TEXT TEXT,");");
});
} catch (e) {
print("Error : " + e.toString());
}
}
}
Best

Answer 1

Database versioning in sqflite matches what has been done in Android where the version is a constant for a particular version of your app with a particular schema. onCreate/onUpgrade should typically get called only once in the lifecyle of your application. Anyway it won't get called unless you close and re-open your database. See https://github.com/tekartik/sqflite/blob/master/sqflite/doc/migration_example.md.
So I would say that the user version as it exists now does not match your need. So I would not used this value nor onUpgrade in your scenario. However you could defined your own singleton value (i.e. your own versioning system) and drop/create table in a transaction while the database is open. Nothing prevents you from doing that.