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1import 'dart:io';
2
3import 'package:path/path.dart';
4import 'package:sqflite/sqflite.dart';
5import 'package:path_provider/path_provider.dart';
6
7class DatabaseHelper {
8  
9  static final _databaseName = "MyDatabase.db";
10  static final _databaseVersion = 1;
11
12  static final table = 'my_table';
13  
14  static final columnId = '_id';
15  static final columnName = 'name';
16  static final columnAge = 'age';
17
18  // make this a singleton class
19  DatabaseHelper._privateConstructor();
20  static final DatabaseHelper instance = DatabaseHelper._privateConstructor();
21
22  // only have a single app-wide reference to the database
23  static Database _database;
24  Future<Database> get database async {
25    if (_database != null) return _database;
26    // lazily instantiate the db the first time it is accessed
27    _database = await _initDatabase();
28    return _database;
29  }
30  
31  // this opens the database (and creates it if it doesn't exist)
32  _initDatabase() async {
33    Directory documentsDirectory = await getApplicationDocumentsDirectory();
34    String path = join(documentsDirectory.path, _databaseName);
35    return await openDatabase(path,
36        version: _databaseVersion,
37        onCreate: _onCreate);
38  }
39
40  // SQL code to create the database table
41  Future _onCreate(Database db, int version) async {
42    await db.execute('''
43          CREATE TABLE $table (
44            $columnId INTEGER PRIMARY KEY,
45            $columnName TEXT NOT NULL,
46            $columnAge INTEGER NOT NULL
47          )
48          ''');
49  }
50  
51  // Helper methods
52
53  // Inserts a row in the database where each key in the Map is a column name
54  // and the value is the column value. The return value is the id of the
55  // inserted row.
56  Future<int> insert(Map<String, dynamic> row) async {
57    Database db = await instance.database;
58    return await db.insert(table, row);
59  }
60
61  // All of the rows are returned as a list of maps, where each map is 
62  // a key-value list of columns.
63  Future<List<Map<String, dynamic>>> queryAllRows() async {
64    Database db = await instance.database;
65    return await db.query(table);
66  }
67
68  // All of the methods (insert, query, update, delete) can also be done using
69  // raw SQL commands. This method uses a raw query to give the row count.
70  Future<int> queryRowCount() async {
71    Database db = await instance.database;
72    return Sqflite.firstIntValue(await db.rawQuery('SELECT COUNT(*) FROM $table'));
73  }
74
75  // We are assuming here that the id column in the map is set. The other 
76  // column values will be used to update the row.
77  Future<int> update(Map<String, dynamic> row) async {
78    Database db = await instance.database;
79    int id = row[columnId];
80    return await db.update(table, row, where: '$columnId = ?', whereArgs: [id]);
81  }
82
83  // Deletes the row specified by the id. The number of affected rows is 
84  // returned. This should be 1 as long as the row exists.
85  Future<int> delete(int id) async {
86    Database db = await instance.database;
87    return await db.delete(table, where: '$columnId = ?', whereArgs: [id]);
88  }
89}