Initial support for generated columns

drift/CHANGELOG.md

@@ -7,6 +7,7 @@
   Thanks to [@westito](https://github.com/westito).
 - Allow the generator to emit correct SQL code when using arrays with the
   `new_sql_code_generation` option in specific scenarios.
+- Add the `generatedAs` method to declare generated columns for Dart tables.
 - Improved support for pausing query stream subscriptions. Instead of buffering events,
   query streams will suspend fetching data if all listeners are paused.
 

drift/lib/src/dsl/columns.dart

@@ -62,32 +62,22 @@ typedef BlobColumn = Column<Uint8List?>;
 /// A column that stores floating point numeric values.
 typedef RealColumn = Column<double?>;
 
+class _BaseColumnBuilder<T> {}
+
 /// A column builder is used to specify which columns should appear in a table.
 /// All of the methods defined in this class and its subclasses are not meant to
 /// be called at runtime. Instead, the generator will take a look at your
 /// source code (specifically, it will analyze which of the methods you use) to
 /// figure out the column structure of a table.
-class ColumnBuilder<T> {}
+class ColumnBuilder<T> extends _BaseColumnBuilder<T> {}
+
+/// A column builder for virtual, generated columns.
+///
+/// This is a different class so that some methods are not available
+class VirtualColumnBuilder<T> extends _BaseColumnBuilder<T> {}
 
 /// DSL extension to define a column inside a drift table.
 extension BuildColumn<T> on ColumnBuilder<T> {
-  /// By default, the field name will be used as the column name, e.g.
-  /// `IntColumn get id = integer()` will have "id" as its associated name.
-  /// Columns made up of multiple words are expected to be in camelCase and will
-  /// be converted to snake_case (e.g. a getter called accountCreationDate will
-  /// result in an SQL column called account_creation_date).
-  /// To change this default behavior, use something like
-  /// `IntColumn get id = integer((c) => c.named('user_id'))`.
-  ///
-  /// Note that using [named] __does not__ have an effect on the json key of an
-  /// object. To change the json key, annotate this column getter with
-  /// [JsonKey].
-  ColumnBuilder<T> named(String name) => _isGenerated();
-
-  /// Marks this column as nullable. Nullable columns should not appear in a
-  /// primary key. Columns are non-null by default.
-  ColumnBuilder<T?> nullable() => _isGenerated();
-
   /// Tells drift to write a custom constraint after this column definition when
   /// writing this column, for instance in a CREATE TABLE statement.
   ///
@@ -164,45 +154,6 @@ extension BuildColumn<T> on ColumnBuilder<T> {
   /// apply the default value.
   ColumnBuilder<T> clientDefault(T Function() onInsert) => _isGenerated();
 
-  /// Uses a custom [converter] to store custom Dart objects in a single column
-  /// and automatically mapping them from and to sql.
-  ///
-  /// An example might look like this:
-  /// ```dart
-  ///  // this is the custom object with we want to store in a column. It
-  ///  // can be as complex as you want it to be
-  ///  class MyCustomObject {
-  ///   final String data;
-  ///   MyCustomObject(this.data);
-  /// }
-  ///
-  /// class CustomConverter extends TypeConverter<MyCustomObject, String> {
-  ///   // this class is responsible for turning a custom object into a string.
-  ///   // this is easy here, but more complex objects could be serialized using
-  ///   // json or any other method of your choice.
-  ///   const CustomConverter();
-  ///   @override
-  ///   MyCustomObject mapToDart(String fromDb) {
-  ///     return fromDb == null ? null : MyCustomObject(fromDb);
-  ///   }
-  ///
-  ///   @override
-  ///   String mapToSql(MyCustomObject value) {
-  ///     return value?.data;
-  ///   }
-  /// }
-  ///
-  /// ```
-  ///
-  /// In that case, you could have a table with this column
-  /// ```dart
-  /// TextColumn get custom => text().map(const CustomConverter())();
-  /// ```
-  /// The generated row class will then use a `MyFancyClass` instead of a
-  /// `String`, which would usually be used for [Table.text] columns.
-  ColumnBuilder<T> map<Dart>(TypeConverter<Dart, T> converter) =>
-      _isGenerated();
-
   /// Adds a foreign-key reference from this column.
   ///
   /// The [table] type must be a Dart class name defining a drift table.
@@ -242,6 +193,104 @@ extension BuildColumn<T> on ColumnBuilder<T> {
     _isGenerated();
   }
 
+  /// Declare a generated column.
+  ///
+  /// Generated columns are backed by an expression, declared with
+  /// [generatedAs]:
+  ///
+  /// ```dart
+  /// class Products extends Table {
+  ///   TextColumn get name => text()();
+  ///
+  ///   RealColumn get price => real()();
+  ///   RealColumn get discount => real()();
+  ///   RealColumn get tax => real()();
+  ///   RealColumn get netPrice => real().generatedAs(
+  ///     price * (Constant(1) - discount) * (Constant(1) + tax))();
+  /// }
+  /// ```
+  ///
+  /// Generated columns can either be `VIRTUAL` (the default) or `STORED`
+  /// (enabled with the [stored] parameter). Stored generated columns are
+  /// computed on each update and are stored in the database. Virtual columns
+  /// consume less space, but are re-computed on each read.
+  ///
+  /// Generated columns can't be updated or inserted (neither with the Dart API
+  /// or though SQL queries), so they are not represented in companions.
+  ///
+  /// __Important__: When a generated column can be nullable, don't forget to
+  /// call [BuildGeneralColumn.nullable] on it to reflect this in the generated
+  /// code.
+  /// Also, note that generated columns are part of your databases schema and
+  /// cannot be updated easily. When changing the [generatedAs] expression for a
+  /// column, you need to re-generate the table with a [TableMigration].
+  ///
+  /// Note that generated columns are only available in sqlite3 version
+  /// `3.31.0`. When using `sqlite3_flutter_libs` or a web database, this is not
+  /// a problem.
+  VirtualColumnBuilder<T> generatedAs(Expression<T?> generatedAs,
+          {bool stored = false}) =>
+      _isGenerated();
+}
+
+/// Column builders available for both virtual and non-virtual columns.
+extension BuildGeneralColumn<T> on _BaseColumnBuilder<T> {
+  /// By default, the field name will be used as the column name, e.g.
+  /// `IntColumn get id = integer()` will have "id" as its associated name.
+  /// Columns made up of multiple words are expected to be in camelCase and will
+  /// be converted to snake_case (e.g. a getter called accountCreationDate will
+  /// result in an SQL column called account_creation_date).
+  /// To change this default behavior, use something like
+  /// `IntColumn get id = integer((c) => c.named('user_id'))`.
+  ///
+  /// Note that using [named] __does not__ have an effect on the json key of an
+  /// object. To change the json key, annotate this column getter with
+  /// [JsonKey].
+  ColumnBuilder<T> named(String name) => _isGenerated();
+
+  /// Marks this column as nullable. Nullable columns should not appear in a
+  /// primary key. Columns are non-null by default.
+  ColumnBuilder<T?> nullable() => _isGenerated();
+
+  /// Uses a custom [converter] to store custom Dart objects in a single column
+  /// and automatically mapping them from and to sql.
+  ///
+  /// An example might look like this:
+  /// ```dart
+  ///  // this is the custom object with we want to store in a column. It
+  ///  // can be as complex as you want it to be
+  ///  class MyCustomObject {
+  ///   final String data;
+  ///   MyCustomObject(this.data);
+  /// }
+  ///
+  /// class CustomConverter extends TypeConverter<MyCustomObject, String> {
+  ///   // this class is responsible for turning a custom object into a string.
+  ///   // this is easy here, but more complex objects could be serialized using
+  ///   // json or any other method of your choice.
+  ///   const CustomConverter();
+  ///   @override
+  ///   MyCustomObject mapToDart(String fromDb) {
+  ///     return fromDb == null ? null : MyCustomObject(fromDb);
+  ///   }
+  ///
+  ///   @override
+  ///   String mapToSql(MyCustomObject value) {
+  ///     return value?.data;
+  ///   }
+  /// }
+  ///
+  /// ```
+  ///
+  /// In that case, you could have a table with this column
+  /// ```dart
+  /// TextColumn get custom => text().map(const CustomConverter())();
+  /// ```
+  /// The generated row class will then use a `MyFancyClass` instead of a
+  /// `String`, which would usually be used for [Table.text] columns.
+  ColumnBuilder<T> map<Dart>(TypeConverter<Dart, T> converter) =>
+      _isGenerated();
+
   /// Turns this column builder into a column. This method won't actually be
   /// called in your code. Instead, the generator will take a look at your
   /// source code to figure out your table structure.

drift/lib/src/runtime/query_builder/schema/column_impl.dart

@@ -44,6 +44,10 @@ class GeneratedColumn<T> extends Column<T> {
   /// The sql type name, such as TEXT for texts.
   final String typeName;
 
+  /// If this column is generated (that is, it is a SQL expression of other)
+  /// columns, contains information about how to generate this column.
+  final GeneratedAs? generatedAs;
+
   /// Whether a value is required for this column when inserting a new row.
   final bool requiredDuringInsert;
 
@@ -67,6 +71,7 @@ class GeneratedColumn<T> extends Column<T> {
     this.defaultValue,
     this.additionalChecks,
     this.requiredDuringInsert = false,
+    this.generatedAs,
   }) : _defaultConstraints = defaultConstraints;
 
   /// Applies a type converter to this column.
@@ -86,6 +91,7 @@ class GeneratedColumn<T> extends Column<T> {
       defaultValue,
       additionalChecks,
       requiredDuringInsert,
+      generatedAs,
     );
   }
 
@@ -111,6 +117,15 @@ class GeneratedColumn<T> extends Column<T> {
         if (writeBrackets) into.buffer.write(')');
       }
 
+      final generated = generatedAs;
+      if (generated != null) {
+        into.buffer.write(' GENERATED ALWAYS AS (');
+        generated.generatedAs.writeInto(into);
+        into.buffer
+          ..write(') ')
+          ..write(generated.stored ? 'STORED' : 'VIRTUAL');
+      }
+
       // these custom constraints refer to builtin constraints from drift
       if (_defaultConstraints != null) {
         into.buffer
@@ -221,6 +236,7 @@ class GeneratedColumnWithTypeConverter<D, S> extends GeneratedColumn<S> {
     Expression<S>? defaultValue,
     VerificationResult Function(S, VerificationMeta)? additionalChecks,
     bool requiredDuringInsert,
+    GeneratedAs? generatedAs,
   ) : super(
           name,
           tableName,
@@ -232,6 +248,7 @@ class GeneratedColumnWithTypeConverter<D, S> extends GeneratedColumn<S> {
           defaultValue: defaultValue,
           additionalChecks: additionalChecks,
           requiredDuringInsert: requiredDuringInsert,
+          generatedAs: generatedAs,
         );
 
   /// Compares this column against the mapped [dartValue].
@@ -241,3 +258,17 @@ class GeneratedColumnWithTypeConverter<D, S> extends GeneratedColumn<S> {
     return equals(converter.mapToSql(dartValue) as S);
   }
 }
+
+/// Information filled out by the generator to support generated or virtual
+/// columns.
+class GeneratedAs {
+  /// The expression that this column evaluates to.
+  final Expression generatedAs;
+
+  /// Wehter this column is stored in the database, as opposed to being
+  /// `VIRTUAL` and evaluated on each read.
+  final bool stored;
+
+  /// Creates a [GeneratedAs] clause.
+  GeneratedAs(this.generatedAs, this.stored);
+}

drift/pubspec.yaml

@@ -1,6 +1,6 @@
 name: drift
 description: Drift is a reactive library to store relational data in Dart and Flutter applications.
-version: 1.0.0
+version: 1.1.0-dev
 repository: https://github.com/simolus3/moor
 homepage: https://drift.simonbinder.eu/
 issue_tracker: https://github.com/simolus3/moor/issues

drift/test/data/tables/todos.dart

@@ -38,6 +38,9 @@ class Categories extends Table with AutoIncrement {
       text().named('desc').customConstraint('NOT NULL UNIQUE')();
   IntColumn get priority =>
       intEnum<CategoryPriority>().withDefault(const Constant(0))();
+
+  TextColumn get descriptionInUpperCase =>
+      text().generatedAs(description.upper())();
 }
 
 enum CategoryPriority { low, medium, high }

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

@@ -11,8 +11,12 @@ class Category extends DataClass implements Insertable<Category> {
   final int id;
   final String description;
   final CategoryPriority priority;
+  final String descriptionInUpperCase;
   Category(
-      {required this.id, required this.description, required this.priority});
+      {required this.id,
+      required this.description,
+      required this.priority,
+      required this.descriptionInUpperCase});
   factory Category.fromData(Map<String, dynamic> data, {String? prefix}) {
     final effectivePrefix = prefix ?? '';
     return Category(
@@ -22,6 +26,8 @@ class Category extends DataClass implements Insertable<Category> {
           .mapFromDatabaseResponse(data['${effectivePrefix}desc'])!,
       priority: $CategoriesTable.$converter0.mapToDart(const IntType()
           .mapFromDatabaseResponse(data['${effectivePrefix}priority']))!,
+      descriptionInUpperCase: const StringType().mapFromDatabaseResponse(
+          data['${effectivePrefix}description_in_upper_case'])!,
     );
   }
   @override
@@ -51,6 +57,8 @@ class Category extends DataClass implements Insertable<Category> {
       id: serializer.fromJson<int>(json['id']),
       description: serializer.fromJson<String>(json['description']),
       priority: serializer.fromJson<CategoryPriority>(json['priority']),
+      descriptionInUpperCase:
+          serializer.fromJson<String>(json['descriptionInUpperCase']),
     );
   }
   factory Category.fromJsonString(String encodedJson,
@@ -65,35 +73,45 @@ class Category extends DataClass implements Insertable<Category> {
       'id': serializer.toJson<int>(id),
       'description': serializer.toJson<String>(description),
       'priority': serializer.toJson<CategoryPriority>(priority),
+      'descriptionInUpperCase':
+          serializer.toJson<String>(descriptionInUpperCase),
     };
   }
 
   Category copyWith(
-          {int? id, String? description, CategoryPriority? priority}) =>
+          {int? id,
+          String? description,
+          CategoryPriority? priority,
+          String? descriptionInUpperCase}) =>
       Category(
         id: id ?? this.id,
         description: description ?? this.description,
         priority: priority ?? this.priority,
+        descriptionInUpperCase:
+            descriptionInUpperCase ?? this.descriptionInUpperCase,
       );
   @override
   String toString() {
     return (StringBuffer('Category(')
           ..write('id: $id, ')
           ..write('description: $description, ')
-          ..write('priority: $priority')
+          ..write('priority: $priority, ')
+          ..write('descriptionInUpperCase: $descriptionInUpperCase')
           ..write(')'))
         .toString();
   }
 
   @override
-  int get hashCode => Object.hash(id, description, priority);
+  int get hashCode =>
+      Object.hash(id, description, priority, descriptionInUpperCase);
   @override
   bool operator ==(Object other) =>
       identical(this, other) ||
       (other is Category &&
           other.id == this.id &&
           other.description == this.description &&
-          other.priority == this.priority);
+          other.priority == this.priority &&
+          other.descriptionInUpperCase == this.descriptionInUpperCase);
 }
 
 class CategoriesCompanion extends UpdateCompanion<Category> {
@@ -185,8 +203,16 @@ class $CategoriesTable extends Categories
               requiredDuringInsert: false,
               defaultValue: const Constant(0))
           .withConverter<CategoryPriority>($CategoriesTable.$converter0);
+  final VerificationMeta _descriptionInUpperCaseMeta =
+      const VerificationMeta('descriptionInUpperCase');
+  late final GeneratedColumn<String?> descriptionInUpperCase =
+      GeneratedColumn<String?>('description_in_upper_case', aliasedName, false,
+          typeName: 'TEXT',
+          requiredDuringInsert: false,
+          generatedAs: GeneratedAs(description.upper(), false));
   @override
-  List<GeneratedColumn> get $columns => [id, description, priority];
+  List<GeneratedColumn> get $columns =>
+      [id, description, priority, descriptionInUpperCase];
   @override
   String get aliasedName => _alias ?? 'categories';
   @override
@@ -206,6 +232,12 @@ class $CategoriesTable extends Categories
       context.missing(_descriptionMeta);
     }
     context.handle(_priorityMeta, const VerificationResult.success());
+    if (data.containsKey('description_in_upper_case')) {
+      context.handle(
+          _descriptionInUpperCaseMeta,
+          descriptionInUpperCase.isAcceptableOrUnknown(
+              data['description_in_upper_case']!, _descriptionInUpperCaseMeta));
+    }
     return context;
   }
 

drift/test/data_class_test.dart

@@ -81,6 +81,7 @@ void main() {
       id: 3,
       description: 'description',
       priority: CategoryPriority.low,
+      descriptionInUpperCase: 'ignored',
     );
     final companion = entry.toCompanion(false);
 

drift/test/insert_test.dart

@@ -386,6 +386,7 @@ void main() {
         {
           'id': 1,
           'desc': 'description',
+          'description_in_upper_case': 'DESCRIPTION',
           'priority': 1,
         },
       ]),

drift/test/integration_tests/insert_integration_test.dart

@@ -107,6 +107,7 @@ void main() {
         id: 1,
         description: 'Description',
         priority: CategoryPriority.low,
+        descriptionInUpperCase: 'DESCRIPTION',
       ),
     );
   }, skip: ifOlderThanSqlite335());

drift/test/join_test.dart

@@ -26,7 +26,8 @@ void main() {
         'SELECT t.id AS "t.id", t.title AS "t.title", '
         't.content AS "t.content", t.target_date AS "t.target_date", '
         't.category AS "t.category", c.id AS "c.id", c."desc" AS "c.desc", '
-        'c.priority AS "c.priority" '
+        'c.priority AS "c.priority", '
+        'c.description_in_upper_case AS "c.description_in_upper_case" '
         'FROM todos t LEFT OUTER JOIN categories c ON c.id = t.category;',
         argThat(isEmpty)));
   });
@@ -46,6 +47,7 @@ void main() {
           't.category': 3,
           'c.id': 3,
           'c.desc': 'description',
+          'c.description_in_upper_case': 'DESCRIPTION',
           'c.priority': 2,
         }
       ]);
@@ -74,6 +76,7 @@ void main() {
         id: 3,
         description: 'description',
         priority: CategoryPriority.high,
+        descriptionInUpperCase: 'DESCRIPTION',
       ),
     );
 
@@ -198,15 +201,22 @@ void main() {
 
     when(executor.runSelect(any, any)).thenAnswer((_) async {
       return [
-        {'c.id': 3, 'c.desc': 'Description', 'c.priority': 1, 'c3': 11}
+        {
+          'c.id': 3,
+          'c.desc': 'Description',
+          'c.description_in_upper_case': 'DESCRIPTION',
+          'c.priority': 1,
+          'c4': 11
+        }
       ];
     });
 
     final result = await query.getSingle();
 
     verify(executor.runSelect(
-      'SELECT c.id AS "c.id", c."desc" AS "c.desc", c.priority AS "c.priority"'
+      'SELECT c.id AS "c.id", c."desc" AS "c.desc", '
-      ', LENGTH(c."desc") AS "c3" '
+      'c.priority AS "c.priority", c.description_in_upper_case AS '
+      '"c.description_in_upper_case", LENGTH(c."desc") AS "c4" '
       'FROM categories c;',
       [],
     ));
@@ -217,6 +227,7 @@ void main() {
         Category(
           id: 3,
           description: 'Description',
+          descriptionInUpperCase: 'DESCRIPTION',
           priority: CategoryPriority.medium,
         ),
       ),
@@ -239,7 +250,13 @@ void main() {
 
     when(executor.runSelect(any, any)).thenAnswer((_) async {
       return [
-        {'c.id': 3, 'c.desc': 'Description', 'c.priority': 1, 'c3': 11}
+        {
+          'c.id': 3,
+          'c.desc': 'Description',
+          'c.description_in_upper_case': 'DESCRIPTION',
+          'c.priority': 1,
+          'c4': 11,
+        },
       ];
     });
 
@@ -247,7 +264,8 @@ void main() {
 
     verify(executor.runSelect(
       'SELECT c.id AS "c.id", c."desc" AS "c.desc", c.priority AS "c.priority"'
-      ', LENGTH(c."desc") AS "c3" '
+      ', c.description_in_upper_case AS "c.description_in_upper_case", '
+      'LENGTH(c."desc") AS "c4" '
       'FROM categories c '
       'INNER JOIN todos t ON c.id = t.category;',
       [],
@@ -259,6 +277,7 @@ void main() {
         Category(
           id: 3,
           description: 'Description',
+          descriptionInUpperCase: 'DESCRIPTION',
           priority: CategoryPriority.medium,
         ),
       ),
@@ -287,7 +306,13 @@ void main() {
 
     when(executor.runSelect(any, any)).thenAnswer((_) async {
       return [
-        {'c.id': 3, 'c.desc': 'desc', 'c.priority': 0, 'c3': 10}
+        {
+          'c.id': 3,
+          'c.desc': 'desc',
+          'c.priority': 0,
+          'c4': 10,
+          'c.description_in_upper_case': 'DESC',
+        }
       ];
     });
 
@@ -295,7 +320,9 @@ void main() {
 
     verify(executor.runSelect(
         'SELECT c.id AS "c.id", c."desc" AS "c.desc", '
-        'c.priority AS "c.priority", COUNT(t.id) AS "c3" '
+        'c.priority AS "c.priority", '
+        'c.description_in_upper_case AS "c.description_in_upper_case", '
+        'COUNT(t.id) AS "c4" '
         'FROM categories c INNER JOIN todos t ON t.category = c.id '
         'GROUP BY c.id HAVING COUNT(t.id) >= ?;',
         [10]));
@@ -306,6 +333,7 @@ void main() {
       Category(
         id: 3,
         description: 'desc',
+        descriptionInUpperCase: 'DESC',
         priority: CategoryPriority.low,
       ),
     );

drift/test/schema_test.dart

@@ -30,7 +30,10 @@ void main() {
           'CREATE TABLE IF NOT EXISTS categories '
           '(id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, '
           '"desc" TEXT NOT NULL UNIQUE, '
-          'priority INTEGER NOT NULL DEFAULT 0);',
+          'priority INTEGER NOT NULL DEFAULT 0, '
+          'description_in_upper_case TEXT NOT NULL GENERATED ALWAYS AS '
+          '(UPPER("desc")) VIRTUAL'
+          ');',
           []));
 
       verify(mockExecutor.runCustom(

drift/test/select_test.dart

@@ -175,6 +175,7 @@ void main() {
         {
           'id': 1,
           'desc': 'description',
+          'description_in_upper_case': 'DESCRIPTION',
           'priority': 2,
         }
       ]);
@@ -187,6 +188,7 @@ void main() {
       Category(
         id: 1,
         description: 'description',
+        descriptionInUpperCase: 'DESCRIPTION',
         priority: CategoryPriority.high,
       ),
     );

drift/test/streams_test.dart

@@ -88,7 +88,12 @@ void main() {
       await first.first; // subscribe to first stream, then drop subscription
 
       when(executor.runSelect(any, any)).thenAnswer((_) => Future.value([
-            {'id': 1, 'desc': 'd', 'priority': 0}
+            {
+              'id': 1,
+              'desc': 'd',
+              'description_in_upper_case': 'D',
+              'priority': 0,
+            }
           ]));
       await db
           .into(db.categories)
@@ -104,7 +109,12 @@ void main() {
       final subscription = first.listen((_) {});
 
       when(executor.runSelect(any, any)).thenAnswer((_) => Future.value([
-            {'id': 1, 'desc': 'd', 'priority': 0}
+            {
+              'id': 1,
+              'desc': 'd',
+              'description_in_upper_case': 'D',
+              'priority': 0,
+            }
           ]));
       await db
           .into(db.categories)
@@ -246,7 +256,12 @@ void main() {
 
       // Return a new row on the next select
       when(executor.runSelect(any, any)).thenAnswer((_) => Future.value([
-            {'id': 1, 'desc': 'd', 'priority': 0}
+            {
+              'id': 1,
+              'desc': 'd',
+              'description_in_upper_case': 'D',
+              'priority': 0,
+            }
           ]));
       db.markTablesUpdated([db.categories]);
       await pumpEventQueue();

drift/test/tables_test.dart

@@ -35,20 +35,15 @@ void main() {
   });
 
   test('can convert a companion to a row class', () {
-    const companion = CategoriesCompanion(
+    const companion = SharedTodosCompanion(
-      id: Value(3),
+      todo: Value(3),
-      description: Value('description'),
+      user: Value(4),
-      priority: Value(CategoryPriority.low),
     );
 
-    final user = db.categories.mapFromCompanion(companion);
+    final user = db.sharedTodos.mapFromCompanion(companion);
     expect(
       user,
-      Category(
+      SharedTodo(todo: 3, user: 4),
-        id: 3,
-        description: 'description',
-        priority: CategoryPriority.low,
-      ),
     );
   });
 

drift_dev/lib/src/analyzer/dart/column_parser.dart

@@ -27,6 +27,7 @@ const String _methodCustomConstraint = 'customConstraint';
 const String _methodDefault = 'withDefault';
 const String _methodClientDefault = 'clientDefault';
 const String _methodMap = 'map';
+const String _methodGenerated = 'generatedAs';
 
 const String _errorMessage = 'This getter does not create a valid column that '
     'can be parsed by moor. Please refer to the readme from moor to see how '
@@ -70,6 +71,7 @@ class ColumnParser {
     Expression? clientDefaultExpression;
     Expression? createdTypeConverter;
     DartType? typeConverterRuntime;
+    ColumnGeneratedAs? generatedAs;
     var nullable = false;
 
     final foundFeatures = <ColumnFeature>[];
@@ -249,6 +251,32 @@ class ColumnParser {
           createdTypeConverter = expression;
           typeConverterRuntime = type;
           break;
+        case _methodGenerated:
+          Expression? generatedExpression;
+          var stored = false;
+
+          for (final expr in remainingExpr.argumentList.arguments) {
+            if (expr is NamedExpression && expr.name.label.name == 'stored') {
+              final storedValue = expr.expression;
+              if (storedValue is BooleanLiteral) {
+                stored = storedValue.value;
+              } else {
+                base.step.reportError(ErrorInDartCode(
+                  message: 'Must be a boolean literal',
+                  affectedNode: expr,
+                  affectedElement: element,
+                ));
+              }
+            } else {
+              generatedExpression = expr;
+            }
+          }
+
+          if (generatedExpression != null) {
+            final code = element.source!.contents.data
+                .substring(generatedExpression.offset, generatedExpression.end);
+            generatedAs = ColumnGeneratedAs(code, stored);
+          }
       }
 
       // We're not at a starting method yet, so we need to go deeper!
@@ -322,10 +350,11 @@ class ColumnParser {
       typeConverter: converter,
       declaration: DartColumnDeclaration(element, base.step.file),
       documentationComment: docString,
+      generatedAs: generatedAs,
     );
   }
 
-  ColumnType _startMethodToColumnType(String startMethod) {
+  ColumnType _startMethodToColumnType(String name) {
     return const {
       startBool: ColumnType.boolean,
       startString: ColumnType.text,
@@ -334,7 +363,7 @@ class ColumnParser {
       startDateTime: ColumnType.datetime,
       startBlob: ColumnType.blob,
       startReal: ColumnType.real,
-    }[startMethod]!;
+    }[name]!;
   }
 
   String? _readJsonKey(Element getter) {

drift_dev/lib/src/analyzer/moor/create_table_reader.dart

@@ -55,6 +55,7 @@ class CreateTableReader {
       UsedTypeConverter? converter;
       String? defaultValue;
       String? overriddenJsonKey;
+      ColumnGeneratedAs? generatedAs;
 
       final typeName = column.definition?.typeName;
 
@@ -158,6 +159,7 @@ class CreateTableReader {
         typeConverter: converter,
         overriddenJsonName: overriddenJsonKey,
         declaration: declaration,
+        generatedAs: generatedAs,
       );
 
       foundColumns[column.name] = parsed;

drift_dev/lib/src/model/column.dart

@@ -106,6 +106,10 @@ class MoorColumn implements HasDeclaration, HasType {
   /// Stored as a multi line string with leading triple-slashes `///` for every line
   final String? documentationComment;
 
+  final ColumnGeneratedAs? generatedAs;
+
+  bool get isGenerated => generatedAs != null;
+
   /// The column type from the dsl library. For instance, if a table has
   /// declared an `IntColumn`, the matching dsl column name would also be an
   /// `IntColumn`.
@@ -180,6 +184,7 @@ class MoorColumn implements HasDeclaration, HasType {
     this.typeConverter,
     this.declaration,
     this.documentationComment,
+    this.generatedAs,
   });
 }
 
@@ -256,3 +261,10 @@ class ResolvedDartForeignKeyReference extends ColumnFeature {
   ResolvedDartForeignKeyReference(
       this.otherTable, this.otherColumn, this.onUpdate, this.onDelete);
 }
+
+class ColumnGeneratedAs {
+  final String? dartExpression;
+  final bool stored;
+
+  ColumnGeneratedAs(this.dartExpression, this.stored);
+}

drift_dev/lib/src/model/declarations/columns.dart

@@ -10,7 +10,7 @@ class DartColumnDeclaration implements DartDeclaration, ColumnDeclaration {
   @override
   final SourceRange declaration;
 
-  /// In the Dart api, columns declared via getters.
+  /// In the Dart api, columns are declared via getters.
   @override
   final Element element;
 

drift_dev/lib/src/model/table.dart

@@ -169,7 +169,8 @@ class MoorTable extends MoorEntityWithResultSet {
 
     if (column.defaultArgument != null ||
         column.clientDefaultCode != null ||
-        column.nullable) {
+        column.nullable ||
+        column.isGenerated) {
       // default value would be applied, so it's not required for inserts
       return false;
     }

drift_dev/lib/src/writer/tables/data_class_writer.dart

@@ -211,6 +211,9 @@ class DataClassWriter {
       ..write('final map = <String, Expression> {};');
 
     for (final column in table.columns) {
+      // Generated column - cannot be used for inserts or updates
+      if (column.isGenerated) continue;
+
       // We include all columns that are not null. If nullToAbsent is false, we
       // also include null columns. When generating NNBD code, we can include
       // non-nullable columns without an additional null check.
@@ -266,6 +269,9 @@ class DataClassWriter {
       ..write('(');
 
     for (final column in table.columns) {
+      // Generated columns are not parts of companions.
+      if (column.isGenerated) continue;
+
       final dartName = column.dartGetterName;
       _buffer
         ..write(dartName)

drift_dev/lib/src/writer/tables/table_writer.dart

@@ -97,6 +97,16 @@ abstract class TableOrViewWriter {
       additionalParams['clientDefault'] = column.clientDefaultCode!;
     }
 
+    if (column.generatedAs != null) {
+      final generateAs = column.generatedAs!;
+      final code = generateAs.dartExpression;
+
+      if (code != null) {
+        additionalParams['generatedAs'] =
+            'GeneratedAs($code, ${generateAs.stored})';
+      }
+    }
+
     final innerType = column.innerColumnType(options);
     var type = 'GeneratedColumn<$innerType>';
     expressionBuffer

drift_dev/lib/src/writer/tables/update_companion_writer.dart

@@ -10,6 +10,11 @@ class UpdateCompanionWriter {
 
   late StringBuffer _buffer;
 
+  late final List<MoorColumn> columns = [
+    for (final column in table.columns)
+      if (!column.isGenerated) column,
+  ];
+
   UpdateCompanionWriter(this.table, this.scope) {
     _buffer = scope.leaf();
   }
@@ -36,7 +41,7 @@ class UpdateCompanionWriter {
   }
 
   void _writeFields() {
-    for (final column in table.columns) {
+    for (final column in columns) {
       final modifier = scope.options.fieldModifier;
       final type = column.dartTypeCode(scope.generationOptions);
       _buffer.write('$modifier Value<$type> ${column.dartGetterName};\n');
@@ -49,7 +54,7 @@ class UpdateCompanionWriter {
     }
     _buffer.write('${table.getNameForCompanionClass(scope.options)}({');
 
-    for (final column in table.columns) {
+    for (final column in columns) {
       _buffer.write('this.${column.dartGetterName} = const Value.absent(),');
     }
 
@@ -73,7 +78,7 @@ class UpdateCompanionWriter {
     //    @required String b}): a = Value(a), b = Value(b);
     // We don't need to use this. for the initializers, Dart figures that out.
 
-    for (final column in table.columns) {
+    for (final column in columns) {
       final param = column.dartGetterName;
 
       if (table.isColumnRequiredForInsert(column)) {
@@ -106,9 +111,8 @@ class UpdateCompanionWriter {
   void _writeCustomConstructor() {
     // Prefer a .custom constructor, unless there already is a field called
     // "custom", in which case we'll use createCustom
-    final constructorName = table.columns
+    final constructorName =
-            .map((e) => e.dartGetterName)
+        columns.map((e) => e.dartGetterName).any((name) => name == 'custom')
-            .any((name) => name == 'custom')
             ? 'createCustom'
             : 'custom';
 
@@ -117,7 +121,7 @@ class UpdateCompanionWriter {
       ..write('static Insertable<$dartTypeName> $constructorName')
       ..write('({');
 
-    for (final column in table.columns) {
+    for (final column in columns) {
       // todo (breaking change): This should not consider type converters.
       final typeName = column.dartTypeCode(scope.generationOptions);
       final type = scope.nullableType('Expression<$typeName>');
@@ -128,7 +132,7 @@ class UpdateCompanionWriter {
       ..write('}) {\n')
       ..write('return RawValuesInsertable({');
 
-    for (final column in table.columns) {
+    for (final column in columns) {
       _buffer
         ..write('if (${column.dartGetterName} != null)')
         ..write(asDartLiteral(column.name.name))
@@ -143,7 +147,7 @@ class UpdateCompanionWriter {
       ..write(table.getNameForCompanionClass(scope.options))
       ..write(' copyWith({');
     var first = true;
-    for (final column in table.columns) {
+    for (final column in columns) {
       if (!first) {
         _buffer.write(', ');
       }
@@ -157,7 +161,7 @@ class UpdateCompanionWriter {
     _buffer
       ..write('}) {\n') //
       ..write('return ${table.getNameForCompanionClass(scope.options)}(');
-    for (final column in table.columns) {
+    for (final column in columns) {
       final name = column.dartGetterName;
       _buffer.write('$name: $name ?? this.$name,');
     }
@@ -173,7 +177,7 @@ class UpdateCompanionWriter {
 
     const locals = {'map', 'nullToAbsent', 'converter'};
 
-    for (final column in table.columns) {
+    for (final column in columns) {
       final getterName = column.thisIfNeeded(locals);
 
       _buffer.write('if ($getterName.present) {');
@@ -212,7 +216,7 @@ class UpdateCompanionWriter {
   void _writeToString() {
     overrideToString(
       table.getNameForCompanionClass(scope.options),
-      [for (final column in table.columns) column.dartGetterName],
+      [for (final column in columns) column.dartGetterName],
       _buffer,
     );
   }
@@ -237,7 +241,7 @@ class UpdateCompanionWriter {
       final column =
           table.columns.firstWhereOrNull((e) => e.dartGetterName == field.name);
 
-      if (column != null) {
+      if (column != null && !column.isGenerated) {
         final dartName = column.dartGetterName;
         _buffer.write('$dartName: Value (_object.$dartName),\n');
       }