I've been struggling for a while to set up a sqlite database with sqflite in flutter. Code is producing a new instance of the database every time I call the getter method for a database. Here is the code:
class DatabaseProvider {
DatabaseProvider._();
static final DatabaseProvider dbProvider = DatabaseProvider._();
static Database? _database;
Future<Database> get database async => _database ??= await _createDatabase();
}
...
You need to initialize the _database in your getter. So, change it to this:
Future<Database> get database async {
if (_database == null) {
// initialize database from _createDatabase result.
_database = await _createDatabase();
}
// because _database have beeen initialized above,
// then we can use ! to tell that the _database can't be null.
return _database!;
}
Related
I'm a beginner in flutter, i want to use SQlite database using sqflite package in my Flutter App, when I declare the_database variable with this syntax static Database _database; , I get a compilation error saying _database must be initialized except I don't know how to initialize it ?
class AnnonceDataBase {
AnnonceDataBase._();
static final AnnonceDataBase instance = AnnonceDataBase._();
static Database _database;
Future<Database> get database async {
if (_database != null) return _database;
_database = await initDB();
return _database;
}
initDB() async {
WidgetsFlutterBinding.ensureInitialized();
return await openDatabase(
join(await getDatabasesPath(), 'annonce_database.db'),
onCreate: (db, version) {
return db.execute(
"CREATE TABLE annonce (id INTEGER PRIMARY KEY, titre Text,prix INTEGER, description TEXT, idAnnonceur INTEGER, active INTEGER)");
},
version: 1,
);
}
}
I will answer here, because without the code this answer would seem out of context on your other question.
You should replace
static Database _database;
with
static Database? _database;
to mark the static variable as an optional (can be null).
I'm a beginner in flutter, i want to use SQlite database using sqflite package in my Flutter App, when I declare the _database variable with this syntax static Database _database; i got a compilation error saying that i must initialize _database, and when i use this syntax static Database? _database;, i have a compilation error under return _database saying A value of type 'Database?' can't be returned from the function 'database' because it has a return type of 'Future<Database>'. and when i put static late Database _database; i have an error in execution saying Error: LateInitializationError: Field '_database' has not been initialized.
my code is
class AnnonceDataBase {
AnnonceDataBase._();
static final AnnonceDataBase instance = AnnonceDataBase._();
static Database _database;
Future<Database> get database async {
if (_database != null) return _database;
_database = await initDB();
return _database;
}
}
I have modified it a bit but it works for you using a singleton to maintain the state of the database
class AnnonceDataBase {
AnnonceDataBase._();
static final AnnonceDataBase _instance = AnnonceDataBase._();
static Database? _database;
factory AnnonceDataBase() => _instance;
Future<Database> get database async {
if (_database != null) return _database!;
_database = await initDB();
return _database!;
}
Future<Database> initDB() async {
String table1 = "CREATE TABLE IF NOT EXISTS table1(id INTEGER PRIMARY KEY,key TEXT NOT NULL UNIQUE,name TEXT,phone NUMERIC)";
String table2 = "CREATE TABLE IF NOT EXISTS table2(id INTEGER PRIMARY KEY,key TEXT NOT NULL UNIQUE,name TEXT,phone NUMERIC)";
String path = await getDatabasesPath();
// Open the database and save the reference.
final Future<Database> database = openDatabase(
// Set the path to the database. Note: Using the `join` function of the
// plugin `path` is best practice to ensure the path is correct
// built for each platform.
p.join(path, 'admin.db'),
// When the database is first created, create a table to store data
onCreate: (db, version) {
db.execute(table1);
return db.execute(table2);
},
// Set the version. This runs the onCreate function and provides a
// path to perform updates and downgrades on the database.
version: 1,
);
return database;
}
}
You can use it like this
#override
void initState() {
AnnonceDataBase._instance.database; //Initialize when loading the application or in the singleton
super.initState();
}
Create a record
Future<void> addData() async {
Database database = AnnonceDataBase._database!;
database.transaction((txn) async {
await txn.rawInsert('INSERT INTO table1(id,key,name,phone) VALUES(?,?,?,?)', ["1", DateTime.now().toString(), "name", "+5555555"]);
});
}
Read all records
Future<void> readData() async {
Database database = AnnonceDataBase._database!;
List<Map> data = await database.rawQuery("SELECT * FROM table1");
debugPrint("data: $data");
}
I'm a beginner in flutter, i want to use SQlite database using sqflite package in my Flutter App, when I declare the _database variable with this syntax static Database _database; i got a compilation error saying that i must initialize _database, and when i use this syntax static Database? _database;, i have a compilation error under return _database saying A value of type 'Database?' can't be returned from the function 'database' because it has a return type of 'Future<Database>'.
my code is
class AnnonceDataBase {
AnnonceDataBase._();
static final AnnonceDataBase instance = AnnonceDataBase._();
static Database _database;
Future<Database> get database async {
if (_database != null) return _database;
_database = await initDB();
return _database;
}
}
Just use like this.
/// late variable initialization
static late Database _database;
Here is more insight why late keyword is used.
https://blog.gskinner.com/archives/2021/03/flutter-lazy-instantiation-with-the-late-keyword.html
Have Fun!
class AppData {
static const _dbName = '<Database-Name>';
static const _dbVersion = 1;
static const _tableName = '<Table-Name>';
AppData._();
static final AppData instance = AppData._();
static Database? _database;
Future<Database?> get database async {
if (_database != null) {
return _database;
}
_database = await _initializeDatabase();
return _database;
}
Future<Database> _initializeDatabase() async {
Directory directory = await getApplicationDocumentsDirectory();
String path = join(directory.path, _dbName);
return await openDatabase(path, version: _dbVersion, onCreate: _onCreate);
}
Future _onCreate(Database db, int version) async {
try {
const createQuery = '''
CREATE TABLE $_tableName(
/// TODO : <Define table structure here using SQL Query>
);
''';
await db.execute(createQuery);
} catch (e) { }
}
}
in this class while declaring the constructor Repository i get this error 'Non-nullable instance field '_database' must be initialized.
Try adding an initializer expression, or add a field initializer in this constructor, or mark it 'late'' i added late but it doesn't work the same error while declaring the static Database _database .
this is the class Repository
import 'package:sqflite/sqflite.dart';
import 'package:todo/repositories/database_connection.dart';
class Repository {
DatabaseConnection _databaseConnection;
Repository() {
_databaseConnection = DatabaseConnection();
}
static Database _database;
Future<Database> get database async {
if (_database != null) return _database;
_database = await _databaseConnection.setDatabase();
return _database;
}
insertData(table, data) async {
var connection = await database;
return await connection.insert(table,data)
}
and this is the DatabaseConnection
class DatabaseConnection {
setDatabase() async {
var directory = await getApplicationDocumentsDirectory();
var path = join(directory.path, 'db_todo_sqflite');
var database =
await openDatabase(path, version: 1, onCreate: _onCreateDatabase);
return database;
}
_onCreateDatabase(Database database, int version) async {
await database.execute(
"CREATE TABLE categories(id INTEGER KEY , name TEXT , descrption TEXT");
}
}
Your database itself is nullable, so you add a ?
static Database? _database;
That makes the _database nullable, but in your getter you are returning a non nullable instance of Database.
The nullable instance would be Database?
Future<Database?> get database async {
...
}
If you are sure that the _database is initialized, and can't be null at that point you return the value, and tell dart that this value is never null.
static Database? _database;
Future<Database> get database async {
if (_database != null) return _database!;
_database = await _databaseConnection.setDatabase();
return _database!;
}
Note the "!" at the return _database!
See also https://dart.dev/null-safety/understanding-null-safety
And https://dart.dev/tools/diagnostic-messages#unchecked_use_of_nullable_value
You are getting an error because
static Database _database is no nullable
Change the code to
static Database? _database
thank all for the response
this how i correct the code
import 'package:sqflite/sqflite.dart';
import 'package:todo/repositories/database_connection.dart';
class Repository {
DatabaseConnection? _databaseConnection;
Repository() {
_databaseConnection = DatabaseConnection();
}
static Database? _database;
Future<Database?> get database async {
if (_database != null) return _database;
_database = await _databaseConnection!.setDatabase();
return _database! ;
}
insertData(table, data) async {
var connection = await database;
return await connection!.insert(table, data);
}
}
You also can use the late modifier:
late DatabaseConnection _databaseConnection;
Just make sure you set this variable before you try to use it.
I have a .db file in the Documents on the device. It has a particular Sqlite database stored on it. How would I import that database file and replace the old one in Flutter? It always has the same name and the same destination in Documents. Here is the code in the DbHelper.dart that initializes the original database, what I'm looking for is replacing that one with the db file I have of another database in the Documents.
DatabaseProvider._();
static final DatabaseProvider db = DatabaseProvider._();
Database _database;
Future<Database> get database async {
print("database getter called");
if (_database != null) {
return _database;
}
_database = await createDatabase();
return _database;
}
Future<Database> createDatabase() async {
String dbPath = await getDatabasesPath();
return await openDatabase(
join(dbPath, 'oldDB.db'),
version: 1,
onCreate: (Database database, int version) async {
print("Creating table");
await database.execute(
"CREATE TABLE $TABLE_PERSON ("
"$COLUMN_ID INTEGER PRIMARY KEY,"
")",
);}
On another page I have a button, for example IMPORT where I would need to have a function that imports the new database file from Documents and replace the old one and persist. How would I go around doing that the most simple way?
This is function that I thought would work, but I am getting asynchronous errors and a lot more weird errors:
class DbHelper {
Future initDb() async {
final dbPath = await ExtStorage.getExternalStoragePublicDirectory(
ExtStorage.DIRECTORY_DOCUMENTS);
final path = join(dbPath, 'backup.db');
final exist = await databaseExists(path);
if (exist) {
print('db imported');
await openDatabase(path);
}
await openDatabase(path);
}
}