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import 'dart:io' ;
import 'package:path/path.dart' ;
import 'package:sqflite/sqflite.dart' ;
import 'package:path_provider/path_provider.dart' ;
class DatabaseHelper {
static final _databaseName = "MyDatabase.db" ;
static final _databaseVersion = 1 ;
static final table = 'my_table' ;
static final columnId = '_id' ;
static final columnName = 'name' ;
static final columnAge = 'age' ;
// make this a singleton class
DatabaseHelper ._privateConstructor ();
static final DatabaseHelper instance = DatabaseHelper ._privateConstructor ();
// only have a single app-wide reference to the database
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 _initDatabase ();
return _database;
}
// this opens the database (and creates it if it doesn't exist)
_initDatabase () async {
Directory documentsDirectory = await getApplicationDocumentsDirectory ();
String path = join (documentsDirectory.path, _databaseName);
return await openDatabase (path,
version: _databaseVersion,
onCreate: _onCreate);
}
// SQL code to create the database table
Future _onCreate (Database db, int version) async {
await db.execute ('''
CREATE TABLE $table (
$columnId INTEGER PRIMARY KEY,
$columnName TEXT NOT NULL,
$columnAge INTEGER NOT NULL
)
''' );
}
// Helper methods
// Inserts a row in the database where each key in the Map is a column name
// and the value is the column value. The return value is the id of the
// inserted row.
Future <int > insert (Map <String , dynamic > row) async {
Database db = await instance.database;
return await db.insert (table, row);
}
// All of the rows are returned as a list of maps, where each map is
// a key-value list of columns.
Future <List <Map <String , dynamic >>> queryAllRows () async {
Database db = await instance.database;
return await db.query (table);
}
// All of the methods (insert, query, update, delete) can also be done using
// raw SQL commands. This method uses a raw query to give the row count.
Future <int > queryRowCount () async {
Database db = await instance.database;
return Sqflite .firstIntValue (await db.rawQuery ('SELECT COUNT(*) FROM $table ' ));
}
// We are assuming here that the id column in the map is set. The other
// column values will be used to update the row.
Future <int > update (Map <String , dynamic > row) async {
Database db = await instance.database;
int id = row[columnId];
return await db.update (table, row, where: '$columnId = ?' , whereArgs: [id]);
}
// Deletes the row specified by the id. The number of affected rows is
// returned. This should be 1 as long as the row exists.
Future <int > delete (int id) async {
Database db = await instance.database;
return await db.delete (table, where: '$columnId = ?' , whereArgs: [id]);
}
}
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