sqflite _onCreate completes asynchronously

[myxiplx]

I'm having a problem with the way the database helpers initialize, create and update the database. Since these functions are making async calls to _onCreate or _onUpgrade, the get database method is returning the database object to the application before it's ready, which then results in "exception: no such table" errors.

If I make a manual call to "get database", and add a 500ms delay before allowing my application to initialize and read any data everything completes fine, but this is clearly not ideal, and from the database helper examples given I don't see any way to avoid this as the issue seems to be fundamentally linked to how openDatabase calls these functions. I consider myself an amateur coder, so I may be missing something here, but I don't see how this could be working for so many people without errors.

In essence, the "await _initDatabase();" line here does not wait for the database to complete an _onCreate or _onUpgrade action before returning:

  Future<Database> get database async {
    if (_database != null) return _database;
    _database = await _initDatabase();
    return _database;
  }

In my application, if I add some print statements to show the flow, the initial opening of the database generates exceptions on create or upgrade, as the application flow is something like:

Creating database
... table1 created
... table2 created
** _initDatabase completes, and returns database to application **
... table3 created
** Application begins loading data **
... data read from table1
... data read from table2
... data read from table3
... exeption: no such table: table4
... exeption: no such table: table5
... exeption: no such table: table6
... table4 created
... table5 created
... table6 created

[davidmartos96]

It could be because you are missing an await inside your initDatabase method?

Could you share it?

[myxiplx]

Here you go, it's essentially unchanged from the example DatabaseHelper:

  // open the database (will create or upgrade as required)
  _initDatabase() async {
    // The path_provider plugin gets the right directory for Android or iOS.
    Directory documentsDirectory = await getApplicationDocumentsDirectory();
    String path = join(documentsDirectory.path, _databaseName);
    print("Database path:" + path);
    // Open the database. Can also add an onUpdate callback parameter.
    return await openDatabase(path,
        version: _databaseVersion,
        onCreate: _onCreate,        //If the database doesn't exist, SQflite will call the onCreate function
        onUpgrade: _onUpgrade, //This is called if the database version is higher than before
        onDowngrade: _onDowngrade);
  }

[myxiplx]

Aaah, got it! Your question got me thinking down different lines. It wasn't not enough "await" lines, it was too many "async". If I remove async from the _onCreate, _onUpgrade, and _onDowngrade functions it works fine.

[davidmartos96]

Great that you found it! I would recommend you to install a linter such as pedantic or lint from pub.dev. They come with predefined lints that help to avoid some common issues and silly mistakes, some of them regarding Futures and async functions.