Add setup callback for moor ffi

moor/lib/src/ffi/vm_database.dart

@@ -5,6 +5,13 @@ import 'package:sqlite3/sqlite3.dart';
 
 import 'moor_ffi_functions.dart';
 
+/// Signature of a function that can perform setup work on a [database] before
+/// moor is fully ready.
+///
+/// This could be used to, for instance, set encryption keys for SQLCipher
+/// implementations.
+typedef DatabaseSetup = void Function(Database database);
+
 /// A moor database that runs on the Dart VM.
 class VmDatabase extends DelegatedDatabase {
   VmDatabase._(DatabaseDelegate delegate, bool logStatements)
@@ -12,13 +19,28 @@ class VmDatabase extends DelegatedDatabase {
 
   /// Creates a database that will store its result in the [file], creating it
   /// if it doesn't exist.
-  factory VmDatabase(File file, {bool logStatements = false}) {
-    return VmDatabase._(_VmDelegate(file), logStatements);
+  ///
+  /// If [logStatements] is true (defaults to `false`), generated sql statements
+  /// will be printed before executing. This can be useful for debugging.
+  /// The optional [setup] function can be used to perform a setup just after
+  /// the database is opened, before moor is fully ready. This can be used to
+  /// add custom user-defined sql functions or to provide encryption keys in
+  /// SQLCipher implementations.
+  factory VmDatabase(File file,
+      {bool logStatements = false, DatabaseSetup setup}) {
+    return VmDatabase._(_VmDelegate(file, setup), logStatements);
   }
 
   /// Creates an in-memory database won't persist its changes on disk.
-  factory VmDatabase.memory({bool logStatements = false}) {
-    return VmDatabase._(_VmDelegate(null), logStatements);
+  ///
+  /// If [logStatements] is true (defaults to `false`), generated sql statements
+  /// will be printed before executing. This can be useful for debugging.
+  /// The optional [setup] function can be used to perform a setup just after
+  /// the database is opened, before moor is fully ready. This can be used to
+  /// add custom user-defined sql functions or to provide encryption keys in
+  /// SQLCipher implementations.
+  factory VmDatabase.memory({bool logStatements = false, DatabaseSetup setup}) {
+    return VmDatabase._(_VmDelegate(null, setup), logStatements);
   }
 }
 
@@ -26,11 +48,12 @@ class _VmDelegate extends DatabaseDelegate {
   Database _db;
 
   final File file;
+  final DatabaseSetup setup;
 
-  _VmDelegate(this.file);
+  _VmDelegate(this.file, this.setup);
 
   @override
-  final TransactionDelegate transactionDelegate = const NoTransactionDelegate();
+  TransactionDelegate get transactionDelegate => const NoTransactionDelegate();
 
   @override
   DbVersionDelegate versionDelegate;
@@ -46,6 +69,9 @@ class _VmDelegate extends DatabaseDelegate {
       _db = sqlite3.openInMemory();
     }
     _db.useMoorVersions();
+    if (setup != null) {
+      setup(_db);
+    }
     versionDelegate = _VmVersionDelegate(_db);
     return Future.value();
   }

moor/test/ffi/moor_functions_test.dart

@@ -1,3 +1,4 @@
+@TestOn('vm')
 import 'dart:math';
 
 import 'package:moor/src/ffi/moor_ffi_functions.dart';

moor/test/ffi/setup_test.dart

@@ -0,0 +1,21 @@
+@TestOn('vm')
+import 'package:moor/ffi.dart';
+import 'package:test/test.dart';
+
+import '../data/tables/todos.dart';
+
+void main() {
+  test('can use a custom setup function', () async {
+    final executor = VmDatabase.memory(setup: (db) {
+      db.createFunction(
+        functionName: 'my_function',
+        function: (args) => 'hello from Dart',
+      );
+    });
+
+    final db = TodoDb(executor);
+    final row = await db.customSelect('SELECT my_function() AS r;').getSingle();
+
+    expect(row.readString('r'), 'hello from Dart');
+  });
+}