Begin working on the database.

lib/db.dart

@@ -0,0 +1,45 @@
+// https://docs.flutter.dev/cookbook/persistence/sqlite
+
+// SQLite
+import 'dart:async';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_expense_tracker/models/frequency.dart';
+import 'package:path/path.dart';
+import 'package:sqflite/sqflite.dart';
+
+// Local
+import '/models/expense.dart';
+
+void loadDB() async {
+  // Avoid errors caused by flutter upgrade.
+  WidgetsFlutterBinding.ensureInitialized();
+
+  final String frequencies =
+      "'${Frequency.values.map((freq) => freq.title).join("','")}'";
+  print(frequencies);
+
+  // Open the database and store the reference.
+  final database = openDatabase(
+    // Set the path to the database. Note: Using the `join` function from the
+    // `path` package is best practice to ensure the path is correctly
+    // constructed for each platform.
+    join(await getDatabasesPath(), 'expense_tracker.db'),
+
+    onCreate: (db, version) {
+      // Run the CREATE TABLE statement on the database.
+      return db.execute(
+        """
+        CREATE TABLE expense
+          ( id INTEGER PRIMARY KEY
+          , name TEXT
+          , cost DOUBLE
+          , frequency TEXT CHECK(frequency IN ($frequencies) )
+          , description TEXT
+        )""",
+      );
+    },
+    // Set the version. This executes the onCreate function and provides a
+    // path to perform database upgrades and downgrades.
+    version: 1,
+  );
+}