Allow named constructors in custom row classes

moor/lib/src/dsl/table.dart

@@ -144,9 +144,15 @@ class UseRowClass {
   /// or types with arguments, are not allowed.
   final Type type;
 
+  /// The name of the constructor to use.
+  ///
+  /// When this option is not set, the default (unnamed) constructor will be
+  /// used to map database rows to the desired row class.
+  final String constructor;
+
   /// Customize the class used by moor to hold an instance of an annotated
   /// table.
   ///
   /// For details, see the overall documentation on [UseRowClass].
-  const UseRowClass(this.type);
+  const UseRowClass(this.type, {this.constructor = ''});
 }

moor/test/data/tables/todos.dart

@@ -58,7 +58,7 @@ class SharedTodos extends Table {
 
 const _uuid = Uuid();
 
-@UseRowClass(CustomRowClass)
+@UseRowClass(CustomRowClass, constructor: 'map')
 class TableWithoutPK extends Table {
   IntColumn get notReallyAnId => integer()();
   RealColumn get someFloat => real()();
@@ -74,9 +74,13 @@ class CustomRowClass implements Insertable<CustomRowClass> {
 
   final String? notFromDb;
 
-  CustomRowClass(this.notReallyAnId, double someFloat,
-      {required this.custom, this.notFromDb})
-      : anotherName = someFloat; // ignore: prefer_initializing_formals
+  CustomRowClass._(
+      this.notReallyAnId, this.anotherName, this.custom, this.notFromDb);
+
+  factory CustomRowClass.map(int notReallyAnId, double someFloat,
+      {required MyCustomObject custom, String? notFromDb}) {
+    return CustomRowClass._(notReallyAnId, someFloat, custom, notFromDb);
+  }
 
   @override
   Map<String, Expression> toColumns(bool nullToAbsent) {

moor/test/data/tables/todos.g.dart

@@ -1205,7 +1205,7 @@ class $TableWithoutPKTable extends TableWithoutPK
   @override
   CustomRowClass map(Map<String, dynamic> data, {String? tablePrefix}) {
     final effectivePrefix = tablePrefix != null ? '$tablePrefix.' : null;
-    return CustomRowClass(
+    return CustomRowClass.map(
       const IntType()
           .mapFromDatabaseResponse(data['${effectivePrefix}not_really_an_id'])!,
       const RealType()

moor/test/insert_test.dart

@@ -30,9 +30,8 @@ void main() {
 
   test('can insert floating point values', () async {
     // regression test for https://github.com/simolus3/moor/issues/30
-    await db
-        .into(db.tableWithoutPK)
-        .insert(CustomRowClass(42, 3.1415, custom: MyCustomObject('custom')));
+    await db.into(db.tableWithoutPK).insert(
+        CustomRowClass.map(42, 3.1415, custom: MyCustomObject('custom')));
 
     verify(executor.runInsert(
         'INSERT INTO table_without_p_k '

moor_generator/lib/src/analyzer/custom_row_class.dart

@@ -4,14 +4,17 @@ import 'package:analyzer/dart/element/type.dart';
 import 'package:moor_generator/moor_generator.dart';
 import 'package:moor_generator/src/analyzer/errors.dart';
 
-ExistingRowClass /*?*/ validateExistingClass(
-    List<MoorColumn> columns, ClassElement desiredClass, ErrorSink errors) {
-  final ctor = desiredClass.unnamedConstructor;
+ExistingRowClass /*?*/ validateExistingClass(List<MoorColumn> columns,
+    ClassElement desiredClass, String constructor, ErrorSink errors) {
+  final ctor = desiredClass.getNamedConstructor(constructor);
+
   if (ctor == null) {
-    errors.report(ErrorInDartCode(
-      affectedElement: desiredClass,
-      message: 'The desired data class must have an unnamed constructor',
-    ));
+    final msg = constructor == ''
+        ? 'The desired data class must have an unnamed constructor'
+        : 'The desired data class does not have a constructor named '
+            '$constructor';
+
+    errors.report(ErrorInDartCode(affectedElement: desiredClass, message: msg));
     return null;
   }
 

moor_generator/lib/src/analyzer/dart/table_parser.dart

@@ -70,6 +70,7 @@ class TableParser {
 
     String name;
     ClassElement existingClass;
+    String constructorInExistingClass;
 
     if (dataClassName != null) {
       name = dataClassName.getField('name').toStringValue();
@@ -79,6 +80,8 @@ class TableParser {
 
     if (useRowClass != null) {
       final type = useRowClass.getField('type').toTypeValue();
+      constructorInExistingClass =
+          useRowClass.getField('constructor').toStringValue();
 
       if (type is InterfaceType) {
         existingClass = type.element;
@@ -93,7 +96,8 @@ class TableParser {
 
     final verified = existingClass == null
         ? null
-        : validateExistingClass(columns, existingClass, base.step.errors);
+        : validateExistingClass(columns, existingClass,
+            constructorInExistingClass, base.step.errors);
     return _DataClassInformation(name, verified);
   }
 

moor_generator/test/analyzer/dart/custom_row_classes_test.dart

@@ -17,6 +17,16 @@ class RowClass {
   RowClass.create();
 }
 @UseRowClass(RowClass)
+class TableClass extends Table {}
+      ''',
+      'a|lib/invalid_no_named_constructor.dart': '''
+import 'package:moor/moor.dart';
+
+class RowClass {
+  RowClass();
+  RowClass.create();
+}
+@UseRowClass(RowClass, constructor: 'create2')
 class TableClass extends Table {}
       ''',
       'a|lib/mismatching_type.dart': '''
@@ -79,6 +89,16 @@ class TableClass extends Table {
       );
     });
 
+    test('when no constructor with the right name exists', () async {
+      final file =
+          await state.analyze('package:a/invalid_no_named_constructor.dart');
+      expect(
+        file.errors.errors,
+        contains(isA<ErrorInDartCode>().having((e) => e.message, 'message',
+            contains('does not have a constructor named create2'))),
+      );
+    });
+
     test('when a parameter has a mismatching type', () async {
       final file = await state.analyze('package:a/mismatching_type.dart');
       expect(