Initial commit

lib/bups/dbhelper_example.dart

@@ -0,0 +1,88 @@
+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]);
+  }
+}