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