Successfully migrate the application to SQLIte!

lib/db.dart

@@ -1,45 +1,101 @@
 // https://docs.flutter.dev/cookbook/persistence/sqlite
 
 // SQLite
+import 'dart:io';
 import 'dart:async';
-import 'package:flutter/widgets.dart';
-import 'package:flutter_expense_tracker/models/frequency.dart';
 import 'package:path/path.dart';
+import 'package:path_provider/path_provider.dart';
 import 'package:sqflite/sqflite.dart';
 
+import 'package:flutter/material.dart';
+
 // Local
+import '/models/frequency.dart';
 import '/models/expense.dart';
 
-void loadDB() async {
-  // Avoid errors caused by flutter upgrade.
-  WidgetsFlutterBinding.ensureInitialized();
+// Leaned on this example:
+//   https://learnflutterwithme.com/sqlite
+class DatabaseHelper {
+  DatabaseHelper._privateConstructor();
+  static final DatabaseHelper instance = DatabaseHelper._privateConstructor();
 
-  final String frequencies =
-      "'${Frequency.values.map((freq) => freq.title).join("','")}'";
-  print(frequencies);
+  static Database? _db;
+  Future<Database> get db async => _db ??= await _initDatabase();
 
-  // Open the database and store the reference.
-  final database = openDatabase(
-    // Set the path to the database. Note: Using the `join` function from the
-    // `path` package is best practice to ensure the path is correctly
-    // constructed for each platform.
-    join(await getDatabasesPath(), 'expense_tracker.db'),
+  Future<Database> _initDatabase() async {
+    Directory documentsDirectory = await getApplicationDocumentsDirectory();
+    String path = join(documentsDirectory.path, "com_hyperling_expense.db");
+    return await openDatabase(
+      path,
+      version: 1,
+      onCreate: _onCreate,
+    );
+  }
 
-    onCreate: (db, version) {
-      // Run the CREATE TABLE statement on the database.
-      return db.execute(
-        """
+  Future _onCreate(Database db, int version) async {
+    await db.execute("""
         CREATE TABLE expense
           ( id INTEGER PRIMARY KEY
-          , name TEXT
-          , cost DOUBLE
-          , frequency TEXT CHECK(frequency IN ($frequencies) )
+          , name TEXT NOT NULL UNIQUE
+          , cost DOUBLE NOT NULL
+          , frequency TEXT NOT NULL
           , description TEXT
-        )""",
-      );
-    },
-    // Set the version. This executes the onCreate function and provides a
-    // path to perform database upgrades and downgrades.
-    version: 1,
-  );
+        )
+        """);
+  }
+
+  /// Expense Section
+  ///
+  Future<List<Expense>> getExpenses() async {
+    Database db = await instance.db;
+    var expenses = await db.query("expense", orderBy: "name");
+    List<Expense> expenseList = expenses.isNotEmpty
+        ? expenses.map((c) => Expense.fromMap(c)).toList()
+        : [];
+    return expenseList;
+  }
+
+  Future<int> addExpense(Expense expense) async {
+    Database db = await instance.db;
+    return await db.insert(
+      "expense",
+      expense.toMap(),
+    );
+  }
+
+  Future<int> removeExpense(int id) async {
+    Database db = await instance.db;
+    return await db.delete(
+      "expense",
+      where: "id = ?",
+      whereArgs: [id],
+    );
+  }
+
+  Future<int> updateExpense(Expense expense) async {
+    Database db = await instance.db;
+    return await db.update(
+      "expense",
+      expense.toMap(),
+      where: "id = ?",
+      whereArgs: [expense.id],
+    );
+  }
+
+  Future<bool> checkExpenseNameExists(String name) async {
+    Database db = await instance.db;
+    var expenses = await db.query("expense",
+        where: "name = ?", whereArgs: [name],);
+    return expenses.isNotEmpty;
+  }
+
+  ///
+
+  /// Income Section
+  ///
+
+  ///
+  /// Liquid Asset Section
+
+  ///
 }