Merge pull request #1774 from westito/unique-constraint

Unique constraint DSL for Dart tables

docs/lib/snippets/tables/advanced.dart

@@ -0,0 +1,17 @@
+import 'package:drift/drift.dart';
+
+// #docregion unique
+class WithUniqueConstraints extends Table {
+  IntColumn get a => integer().unique()();
+
+  IntColumn get b => integer()();
+  IntColumn get c => integer()();
+
+  @override
+  List<Set<Column>> get uniqueKeys => [
+        {b, c}
+      ];
+
+  // Effectively, this table has two unique key sets: (a) and (b, c).
+}
+// #enddocregion unique

docs/pages/docs/Getting started/advanced_dart_tables.md

@@ -1,7 +1,7 @@
 ---
 data:
   title: "Dart tables"
-  description: Further information on Dart tables
+  description: Further information on defining tables in Dart.
   weight: 150
 template: layouts/docs/single
 ---
@@ -11,6 +11,8 @@ __Prefer sql?__ If you prefer, you can also declare tables via `CREATE TABLE` st
 Drift's sql analyzer will generate matching Dart code. [Details]({{ "starting_with_sql.md" | pageUrl }}).
 {% endblock %}
 
+{% assign snippets = 'package:moor_documentation/snippets/tables/advanced.dart.excerpt.json' | readString | json_decode %}
+
 As shown in the [getting started guide]({{ "index.md" | pageUrl }}), sql tables can be written in Dart:
 ```dart
 class Todos extends Table {
@@ -128,6 +130,19 @@ Note that the primary key must essentially be constant so that the generator can
 - it must be defined with the `=>` syntax, function bodies aren't supported
 - it must return a set literal without collection elements like `if`, `for` or spread operators
 
+## Unique Constraints
+
+Starting from version 1.6.0, `UNIQUE` SQL constraints can be defined on Dart tables too.
+A unique constraint contains one or more columns. The combination of all columns in a constraint
+must be unique in the table, or the databas will report an error on inserts.
+
+With drift, a unique constraint can be added to a single column by marking it as `.unique()` in
+the column builder.
+A unique set spanning multiple columns can be added by overriding the `uniqueKeys` getter in the
+`Table` class:
+
+{% include "blocks/snippet" snippets = snippets name = 'unique' %}
+
 ## Supported column types
 
 Drift supports a variety of column types out of the box. You can store custom classes in columns by using

drift/CHANGELOG.md

@@ -1,5 +1,7 @@
 ## 1.6.0-dev
 
+- Add the `unique()` method to columns and the `uniqueKeys` override to tables
+  to define unique constraints in Dart tables.
 - Add the very experimental `package:drift/wasm.dart` library. It uses WebAssembly
   to access sqlite3 without any external JavaScript libraries, but requires you to
   add a [WebAssembly module](https://github.com/simolus3/sqlite3.dart/tree/main/sqlite3#wasm-web-support)

drift/example/main.g.dart

@@ -172,6 +172,8 @@ class $TodoCategoriesTable extends TodoCategories
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   TodoCategory map(Map<String, dynamic> data, {String? tablePrefix}) {
     return TodoCategory.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -460,6 +462,8 @@ class $TodoItemsTable extends TodoItems
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   TodoItem map(Map<String, dynamic> data, {String? tablePrefix}) {
     return TodoItem.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);

drift/lib/src/dsl/columns.dart

@@ -95,8 +95,8 @@ extension BuildColumn<T> on ColumnBuilder<T> {
   /// [constraint] if that is desired.
   ///
   /// This can be used to implement constraints that drift does not (yet)
-  /// support (e.g. unique keys, etc.). If you've found a common use-case for
+  /// support. If you've found a common use-case for  this, it should be
-  /// this, it should be considered a limitation of drift itself. Please feel
+  /// considered a limitation of drift itself. Please feel
   /// free to open an issue at https://github.com/simolus3/drift/issues/new to
   /// report that.
   ///
@@ -252,6 +252,12 @@ extension BuildGeneralColumn<T> on _BaseColumnBuilder<T> {
   /// primary key. Columns are non-null by default.
   ColumnBuilder<T?> nullable() => _isGenerated();
 
+  /// Adds UNIQUE constraint to column.
+  ///
+  /// Unique constraints spanning multiple keys can be added to a table by
+  /// overriding [Table.uniqueKeys].
+  ColumnBuilder<T?> unique() => _isGenerated();
+
   /// Uses a custom [converter] to store custom Dart objects in a single column
   /// and automatically mapping them from and to sql.
   ///

drift/lib/src/dsl/table.dart

@@ -62,6 +62,34 @@ abstract class Table extends HasResultSet {
   @visibleForOverriding
   Set<Column>? get primaryKey => null;
 
+  /// Unique constraints in this table.
+  ///
+  /// When two rows have the same value in _any_  set specified in [uniqueKeys],
+  /// the database will reject the second row for inserts.
+  ///
+  /// Override this to specify unique keys:
+  ///
+  /// ```dart
+  /// class IngredientInRecipes extends Table {
+  ///  @override
+  ///  Set<Column> get uniqueKeys =>
+  ///     [{recipe, ingredient}, {recipe, amountInGrams}];
+  ///
+  ///  IntColumn get recipe => integer()();
+  ///  IntColumn get ingredient => integer()();
+  ///
+  ///  IntColumn get amountInGrams => integer().named('amount')();
+  /// ```
+  ///
+  /// The getter must return a list of set literals using the `=>` syntax so
+  /// that the drift generator can understand the code.
+  ///
+  /// Note that individual columns can also be marked as unique with
+  /// [BuildGeneralColumn.unique]. This is equivalent to adding a single-element
+  /// set to this list.
+  @visibleForOverriding
+  List<Set<Column>>? get uniqueKeys => null;
+
   /// Custom table constraints that should be added to the table.
   ///
   /// See also:

drift/lib/src/runtime/query_builder/migration.dart

@@ -288,6 +288,21 @@ class Migrator {
       context.buffer.write(')');
     }
 
+    if (table.uniqueKeys.isNotEmpty) {
+      for (final key in table.uniqueKeys) {
+        context.buffer.write(', UNIQUE (');
+        final uqList = key.toList(growable: false);
+        for (var i = 0; i < uqList.length; i++) {
+          final column = uqList[i];
+
+          context.buffer.write(escapeIfNeeded(column.name));
+
+          if (i != uqList.length - 1) context.buffer.write(', ');
+        }
+        context.buffer.write(')');
+      }
+    }
+
     final constraints = dslTable.customConstraints;
 
     for (var i = 0; i < constraints.length; i++) {

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

@@ -28,6 +28,14 @@ mixin TableInfo<TableDsl extends Table, D> on Table
   @override
   Set<Column> get primaryKey => $primaryKey;
 
+  /// The unique key of this table. Can be empty if no custom primary key has
+  /// been specified.
+  ///
+  /// Additional to the [Table.primaryKey] columns declared by an user, this
+  /// also contains auto-increment integers, which are primary key by default.
+  @override
+  List<Set<GeneratedColumn>> get uniqueKeys => const [];
+
   /// The table name in the sql table. This can be an alias for the actual table
   /// name. See [actualTableName] for a table name that is not aliased.
   @Deprecated('Use aliasedName instead')

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

@@ -271,6 +271,8 @@ class ConfigTable extends Table with TableInfo<ConfigTable, Config> {
   @override
   Set<GeneratedColumn> get $primaryKey => {configKey};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   Config map(Map<String, dynamic> data, {String? tablePrefix}) {
     return Config.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -458,6 +460,8 @@ class WithDefaults extends Table with TableInfo<WithDefaults, WithDefault> {
   @override
   Set<GeneratedColumn> get $primaryKey => <GeneratedColumn>{};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   WithDefault map(Map<String, dynamic> data, {String? tablePrefix}) {
     return WithDefault.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -546,6 +550,8 @@ class NoIds extends Table with TableInfo<NoIds, NoIdRow> {
   @override
   Set<GeneratedColumn> get $primaryKey => {payload};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   NoIdRow map(Map<String, dynamic> data, {String? tablePrefix}) {
     final effectivePrefix = tablePrefix != null ? '$tablePrefix.' : '';
     return NoIdRow(
@@ -767,6 +773,8 @@ class WithConstraints extends Table
   @override
   Set<GeneratedColumn> get $primaryKey => <GeneratedColumn>{};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   WithConstraint map(Map<String, dynamic> data, {String? tablePrefix}) {
     return WithConstraint.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -1036,6 +1044,8 @@ class Mytable extends Table with TableInfo<Mytable, MytableData> {
   @override
   Set<GeneratedColumn> get $primaryKey => {someid};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   MytableData map(Map<String, dynamic> data, {String? tablePrefix}) {
     return MytableData.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -1256,6 +1266,8 @@ class Email extends Table
   @override
   Set<GeneratedColumn> get $primaryKey => <GeneratedColumn>{};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   EMail map(Map<String, dynamic> data, {String? tablePrefix}) {
     return EMail.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -1443,6 +1455,8 @@ class WeirdTable extends Table with TableInfo<WeirdTable, WeirdData> {
   @override
   Set<GeneratedColumn> get $primaryKey => <GeneratedColumn>{};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   WeirdData map(Map<String, dynamic> data, {String? tablePrefix}) {
     return WeirdData.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);

drift/test/data/tables/todos.dart

@@ -16,13 +16,19 @@ class TodosTable extends Table with AutoIncrement {
   TextColumn get title => text().withLength(min: 4, max: 16).nullable()();
   TextColumn get content => text()();
   @JsonKey('target_date')
-  DateTimeColumn get targetDate => dateTime().nullable()();
+  DateTimeColumn get targetDate => dateTime().nullable().unique()();
 
   IntColumn get category => integer().references(Categories, #id).nullable()();
+
+  @override
+  List<Set<Column>>? get uniqueKeys => [
+        {title, category},
+        {title, targetDate},
+      ];
 }
 
 class Users extends Table with AutoIncrement {
-  TextColumn get name => text().withLength(min: 6, max: 32)();
+  TextColumn get name => text().withLength(min: 6, max: 32).unique()();
   BoolColumn get isAwesome => boolean().withDefault(const Constant(true))();
 
   BlobColumn get profilePicture => blob()();

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

@@ -249,6 +249,8 @@ class $CategoriesTable extends Categories
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   Category map(Map<String, dynamic> data, {String? tablePrefix}) {
     return Category.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -503,7 +505,9 @@ class $TodosTableTable extends TodosTable
   @override
   late final GeneratedColumn<DateTime?> targetDate = GeneratedColumn<DateTime?>(
       'target_date', aliasedName, true,
-      type: const IntType(), requiredDuringInsert: false);
+      type: const IntType(),
+      requiredDuringInsert: false,
+      defaultConstraints: 'UNIQUE');
   final VerificationMeta _categoryMeta = const VerificationMeta('category');
   @override
   late final GeneratedColumn<int?> category = GeneratedColumn<int?>(
@@ -552,6 +556,11 @@ class $TodosTableTable extends TodosTable
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [
+        {title, category},
+        {title, targetDate},
+      ];
+  @override
   TodoEntry map(Map<String, dynamic> data, {String? tablePrefix}) {
     return TodoEntry.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -782,7 +791,8 @@ class $UsersTable extends Users with TableInfo<$UsersTable, User> {
       additionalChecks:
           GeneratedColumn.checkTextLength(minTextLength: 6, maxTextLength: 32),
       type: const StringType(),
-      requiredDuringInsert: true);
+      requiredDuringInsert: true,
+      defaultConstraints: 'UNIQUE');
   final VerificationMeta _isAwesomeMeta = const VerificationMeta('isAwesome');
   @override
   late final GeneratedColumn<bool?> isAwesome = GeneratedColumn<bool?>(
@@ -850,6 +860,8 @@ class $UsersTable extends Users with TableInfo<$UsersTable, User> {
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   User map(Map<String, dynamic> data, {String? tablePrefix}) {
     return User.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -1030,6 +1042,8 @@ class $SharedTodosTable extends SharedTodos
   @override
   Set<GeneratedColumn> get $primaryKey => {todo, user};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   SharedTodo map(Map<String, dynamic> data, {String? tablePrefix}) {
     return SharedTodo.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -1184,6 +1198,8 @@ class $TableWithoutPKTable extends TableWithoutPK
   @override
   Set<GeneratedColumn> get $primaryKey => <GeneratedColumn>{};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   CustomRowClass map(Map<String, dynamic> data, {String? tablePrefix}) {
     final effectivePrefix = tablePrefix != null ? '$tablePrefix.' : '';
     return CustomRowClass.map(
@@ -1341,6 +1357,8 @@ class $PureDefaultsTable extends PureDefaults
   @override
   Set<GeneratedColumn> get $primaryKey => {txt};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   PureDefault map(Map<String, dynamic> data, {String? tablePrefix}) {
     return PureDefault.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);

drift/test/expressions/expressions_integration_test.dart

@@ -61,7 +61,7 @@ void main() {
         );
     await db.into(db.users).insert(
           UsersCompanion.insert(
-              name: 'User name',
+              name: 'User name 2',
               profilePicture: Uint8List(0),
               creationTime: Value(secondTime)),
         );

drift/test/integration_tests/select_integration_test.dart

@@ -19,7 +19,7 @@ void main() {
       b.insertAll(db.users, [
         for (var i = 0; i < 1000; i++)
           UsersCompanion.insert(
-              name: 'user name', profilePicture: Uint8List(0)),
+              name: 'user name $i', profilePicture: Uint8List(0)),
       ]);
     });
 

drift/test/schema_test.dart

@@ -22,8 +22,9 @@ void main() {
       verify(mockExecutor.runCustom(
           'CREATE TABLE IF NOT EXISTS todos '
           '(id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, title TEXT NULL, '
-          'content TEXT NOT NULL, target_date INTEGER NULL, '
+          'content TEXT NOT NULL, target_date INTEGER NULL UNIQUE, '
-          'category INTEGER NULL REFERENCES categories (id));',
+          'category INTEGER NULL REFERENCES categories (id), '
+          'UNIQUE (title, category), UNIQUE (title, target_date));',
           []));
 
       verify(mockExecutor.runCustom(
@@ -39,7 +40,7 @@ void main() {
       verify(mockExecutor.runCustom(
           'CREATE TABLE IF NOT EXISTS users '
           '(id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, '
-          'name TEXT NOT NULL, '
+          'name TEXT NOT NULL UNIQUE, '
           'is_awesome INTEGER NOT NULL DEFAULT 1 CHECK (is_awesome IN (0, 1)), '
           'profile_picture BLOB NOT NULL, '
           'creation_time INTEGER NOT NULL '
@@ -91,7 +92,7 @@ void main() {
       verify(mockExecutor.runCustom(
           'CREATE TABLE IF NOT EXISTS users '
           '(id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, '
-          'name TEXT NOT NULL, '
+          'name TEXT NOT NULL UNIQUE, '
           'is_awesome INTEGER NOT NULL DEFAULT 1 CHECK (is_awesome IN (0, 1)), '
           'profile_picture BLOB NOT NULL, '
           'creation_time INTEGER NOT NULL '

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

@@ -23,6 +23,7 @@ const String _methodReferences = 'references';
 const String _methodAutoIncrement = 'autoIncrement';
 const String _methodWithLength = 'withLength';
 const String _methodNullable = 'nullable';
+const String _methodUnique = 'unique';
 const String _methodCustomConstraint = 'customConstraint';
 const String _methodDefault = 'withDefault';
 const String _methodClientDefault = 'clientDefault';
@@ -218,6 +219,9 @@ class ColumnParser {
         case _methodNullable:
           nullable = true;
           break;
+        case _methodUnique:
+          foundFeatures.add(const UniqueKey());
+          break;
         case _methodCustomConstraint:
           foundCustomConstraint = base.readStringLiteral(
               remainingExpr.argumentList.arguments.first, () {
@@ -355,6 +359,17 @@ class ColumnParser {
       );
     }
 
+    if (foundFeatures.contains(const UniqueKey()) &&
+        foundFeatures.contains(const PrimaryKey())) {
+      base.step.reportError(
+        ErrorInDartCode(
+          severity: Severity.error,
+          affectedElement: getter.declaredElement,
+          message: 'Primary key column cannot have UNIQUE constraint',
+        ),
+      );
+    }
+
     final docString =
         getter.documentationComment?.tokens.map((t) => t.toString()).join('\n');
     return MoorColumn(

drift_dev/lib/src/analyzer/dart/table_parser.dart

@@ -12,6 +12,7 @@ class TableParser {
 
     final columns = (await _parseColumns(element)).toList();
     final primaryKey = await _readPrimaryKey(element, columns);
+    final uniqueKeys = await _readUniqueKeys(element, columns);
 
     final dataClassInfo = _readDataClassInformation(columns, element);
 
@@ -23,6 +24,7 @@ class TableParser {
       existingRowClass: dataClassInfo.existingClass,
       customParentClass: dataClassInfo.extending,
       primaryKey: primaryKey,
+      uniqueKeys: uniqueKeys,
       overrideWithoutRowId: await _overrideWithoutRowId(element),
       declaration: DartTableDeclaration(element, base.step.file),
     );
@@ -34,6 +36,38 @@ class TableParser {
       ));
     }
 
+    if (primaryKey != null &&
+        primaryKey.length == 1 &&
+        primaryKey.first.features.contains(const UniqueKey())) {
+      base.step.errors.report(ErrorInDartCode(
+        message: 'Primary key column cannot have UNIQUE constraint',
+        affectedElement: element,
+      ));
+    }
+
+    if (uniqueKeys != null &&
+        uniqueKeys.any((key) =>
+            uniqueKeys.length == 1 &&
+            key.first.features.contains(const UniqueKey()))) {
+      base.step.errors.report(ErrorInDartCode(
+        message:
+            'Column provided in a single-column uniqueKey set already has a '
+            'column-level UNIQUE constraint',
+        affectedElement: element,
+      ));
+    }
+
+    if (uniqueKeys != null &&
+        primaryKey != null &&
+        uniqueKeys
+            .any((unique) => const SetEquality().equals(unique, primaryKey))) {
+      base.step.errors.report(ErrorInDartCode(
+        message: 'The uniqueKeys override contains the primary key, which is '
+            'already unique by default.',
+        affectedElement: element,
+      ));
+    }
+
     var index = 0;
     for (final converter in table.converters) {
       converter
@@ -188,6 +222,68 @@ class TableParser {
     return parsedPrimaryKey;
   }
 
+  Future<List<Set<MoorColumn>>?> _readUniqueKeys(
+      ClassElement element, List<MoorColumn> columns) async {
+    final uniqueKeyGetter = element.lookUpGetter('uniqueKeys', element.library);
+
+    if (uniqueKeyGetter == null || uniqueKeyGetter.isFromDefaultTable) {
+      // resolved uniqueKeys is from the Table dsl superclass. That means there
+      // is no unique key list
+      return null;
+    }
+
+    final ast =
+        await base.loadElementDeclaration(uniqueKeyGetter) as MethodDeclaration;
+    final body = ast.body;
+    if (body is! ExpressionFunctionBody) {
+      base.step.reportError(ErrorInDartCode(
+          affectedElement: uniqueKeyGetter,
+          message: 'This must return a list of set literal using the => '
+              'syntax!'));
+      return null;
+    }
+    final expression = body.expression;
+    final parsedUniqueKeys = <Set<MoorColumn>>[];
+
+    if (expression is ListLiteral) {
+      for (final keySet in expression.elements) {
+        if (keySet is SetOrMapLiteral) {
+          final uniqueKey = <MoorColumn>{};
+          for (final entry in keySet.elements) {
+            if (entry is Identifier) {
+              final column = columns.singleWhereOrNull(
+                  (column) => column.dartGetterName == entry.name);
+              if (column == null) {
+                base.step.reportError(
+                  ErrorInDartCode(
+                    affectedElement: uniqueKeyGetter,
+                    affectedNode: entry,
+                    message: 'Column not found in this table',
+                  ),
+                );
+              } else {
+                uniqueKey.add(column);
+              }
+            } else {
+              print('Unexpected entry in expression.elements: $entry');
+            }
+          }
+          parsedUniqueKeys.add(uniqueKey);
+        } else {
+          base.step.reportError(ErrorInDartCode(
+              affectedElement: uniqueKeyGetter,
+              message: 'This must return a set list literal!'));
+        }
+      }
+    } else {
+      base.step.reportError(ErrorInDartCode(
+          affectedElement: uniqueKeyGetter,
+          message: 'This must return a set list literal!'));
+    }
+
+    return parsedUniqueKeys;
+  }
+
   Future<bool?> _overrideWithoutRowId(ClassElement element) async {
     final getter = element.lookUpGetter('withoutRowId', element.library);
 

drift_dev/lib/src/model/column.dart

@@ -203,6 +203,11 @@ class PrimaryKey extends ColumnFeature {
   const PrimaryKey();
 }
 
+/// A `UNIQUE` column constraint.
+class UniqueKey extends ColumnFeature {
+  const UniqueKey();
+}
+
 class AutoIncrement extends PrimaryKey {
   static const AutoIncrement _instance = AutoIncrement._();
 

drift_dev/lib/src/model/table.dart

@@ -92,6 +92,10 @@ class MoorTable extends MoorEntityWithResultSet {
   /// For the full primary key, see [fullPrimaryKey].
   final Set<MoorColumn>? primaryKey;
 
+  /// The set of unique keys if they have been explicitly defined by
+  /// overriding `uniqueKeys` in the table class.
+  final List<Set<MoorColumn>>? uniqueKeys;
+
   /// The primary key for this table.
   ///
   /// Unlikely [primaryKey], this method is not limited to the `primaryKey`
@@ -146,6 +150,7 @@ class MoorTable extends MoorEntityWithResultSet {
     required this.sqlName,
     required this.dartTypeName,
     this.primaryKey,
+    this.uniqueKeys,
     String? overriddenName,
     this.overrideWithoutRowId,
     this.overrideTableConstraints,

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

@@ -28,9 +28,21 @@ abstract class TableOrViewWriter {
               : 'PRIMARY KEY');
 
           wrotePkConstraint = true;
+          break;
         }
       }
+    }
 
+    if (!wrotePkConstraint) {
+      for (final feature in column.features) {
+        if (feature is UniqueKey) {
+          defaultConstraints.add('UNIQUE');
+          break;
+        }
+      }
+    }
+
+    for (final feature in column.features) {
       if (feature is ResolvedDartForeignKeyReference) {
         final tableName = escapeIfNeeded(feature.otherTable.sqlName);
         final columnName = escapeIfNeeded(feature.otherColumn.name.name);
@@ -324,6 +336,7 @@ class TableWriter extends TableOrViewWriter {
 
     _writeValidityCheckMethod();
     _writePrimaryKeyOverride();
+    _writeUniqueKeyOverride();
 
     writeMappingMethod(scope);
     // _writeReverseMappingMethod();
@@ -425,6 +438,32 @@ class TableWriter extends TableOrViewWriter {
     buffer.write('};\n');
   }
 
+  void _writeUniqueKeyOverride() {
+    buffer.write('@override\nList<Set<GeneratedColumn>> get uniqueKeys => ');
+    final uniqueKeys = table.uniqueKeys ?? [];
+
+    if (uniqueKeys.isEmpty) {
+      buffer.write('[];');
+      return;
+    }
+
+    buffer.write('[');
+    for (final uniqueKey in uniqueKeys) {
+      buffer.write('{');
+      final uqList = uniqueKey.toList();
+      for (var i = 0; i < uqList.length; i++) {
+        final pk = uqList[i];
+
+        buffer.write(pk.dartGetterName);
+        if (i != uqList.length - 1) {
+          buffer.write(', ');
+        }
+      }
+      buffer.write('},\n');
+    }
+    buffer.write('];\n');
+  }
+
   void _writeAliasGenerator() {
     final typeName = table.entityInfoName;
 

drift_dev/test/analyzer/dart/unique_columns_test.dart

@@ -0,0 +1,111 @@
+import 'package:test/test.dart';
+
+import '../utils.dart';
+
+void main() {
+  test('does not allow autoIncrement() to have a unique constraint', () async {
+    final state = TestState.withContent({
+      'a|lib/main.dart': '''
+import 'package:drift/drift.dart';
+
+class Test extends Table {
+  IntColumn get a => integer().autoIncrement().unique()();
+}
+'''
+    });
+    addTearDown(state.close);
+
+    (await state.analyze('package:a/main.dart')).expectDartError(
+        'Primary key column cannot have UNIQUE constraint', 'a');
+  });
+
+  test('does not allow primary key to have a unique constraint', () async {
+    final state = TestState.withContent({
+      'a|lib/main.dart': '''
+import 'package:drift/drift.dart';
+
+class Test extends Table {
+  IntColumn get a => integer().unique()();
+
+  @override
+  Set<Column> get primaryKey => {a};
+}
+'''
+    });
+    addTearDown(state.close);
+
+    (await state.analyze('package:a/main.dart')).expectDartError(
+        'Primary key column cannot have UNIQUE constraint', 'Test');
+  });
+
+  test(
+      'does not allow primary key to have a unique constraint through override',
+      () async {
+    final state = TestState.withContent({
+      'a|lib/main.dart': '''
+import 'package:drift/drift.dart';
+
+class Test extends Table {
+  IntColumn get a => integer()();
+
+  @override
+  List<Set<Column>> get uniqueKeys => [{a}];
+
+  @override
+  Set<Column> get primaryKey => {a};
+}
+'''
+    });
+    addTearDown(state.close);
+
+    (await state.analyze('package:a/main.dart')).expectDartError(
+        'The uniqueKeys override contains the primary key, which is already '
+            'unique by default.',
+        'Test');
+  });
+
+  test('warns about duplicate unique declarations', () async {
+    final state = TestState.withContent({
+      'a|lib/main.dart': '''
+import 'package:drift/drift.dart';
+
+class Test extends Table {
+  IntColumn get a => integer().unique()();
+
+  @override
+  List<Set<Column>> get uniqueKeys => [{a}];
+}
+'''
+    });
+    addTearDown(state.close);
+
+    (await state.analyze('package:a/main.dart')).expectDartError(
+        contains('already has a column-level UNIQUE constraint'), 'Test');
+  });
+
+  test('parses unique key definitions', () async {
+    final state = TestState.withContent({
+      'a|lib/main.dart': '''
+import 'package:drift/drift.dart';
+
+class Test extends Table {
+  IntColumn get a => integer().unique()();
+  IntColumn get b => integer().unique()();
+
+  @override
+  List<Set<Column>> get uniqueKeys => [{a}, {b}, {a, b}];
+}
+'''
+    });
+    addTearDown(state.close);
+
+    final file = await state.analyze('package:a/main.dart');
+    expect(file.errors.errors, isEmpty);
+
+    final table = file.currentResult!.declaredTables.single;
+    expect(table.uniqueKeys, hasLength(3));
+    expect(table.uniqueKeys![0].map((e) => e.name.name), ['a']);
+    expect(table.uniqueKeys![1].map((e) => e.name.name), ['b']);
+    expect(table.uniqueKeys![2].map((e) => e.name.name), ['a', 'b']);
+  });
+}

examples/flutter_web_worker_example/lib/src/database/database.g.dart

@@ -166,6 +166,8 @@ class Entries extends Table with TableInfo<Entries, Entrie> {
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   Entrie map(Map<String, dynamic> data, {String? tablePrefix}) {
     return Entrie.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);

examples/migrations_example/lib/database.g.dart

@@ -166,6 +166,8 @@ class $UsersTable extends Users with TableInfo<$UsersTable, User> {
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   User map(Map<String, dynamic> data, {String? tablePrefix}) {
     return User.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -414,6 +416,8 @@ class Groups extends Table with TableInfo<Groups, Group> {
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   Group map(Map<String, dynamic> data, {String? tablePrefix}) {
     return Group.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);

examples/web_worker_example/lib/database.g.dart

@@ -166,6 +166,8 @@ class Entries extends Table with TableInfo<Entries, Entrie> {
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   Entrie map(Map<String, dynamic> data, {String? tablePrefix}) {
     return Entrie.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);

examples/with_built_value/lib/database.drift.dart

@@ -171,6 +171,8 @@ class Users extends Table with TableInfo<Users, User> {
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   User map(Map<String, dynamic> data, {String tablePrefix}) {
     return User.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);

extras/benchmarks/lib/src/moor/database.g.dart

@@ -126,9 +126,10 @@ class KeyValuesCompanion extends UpdateCompanion<KeyValue> {
 
 class $KeyValuesTable extends KeyValues
     with TableInfo<$KeyValuesTable, KeyValue> {
-  final GeneratedDatabase _db;
+  @override
+  final GeneratedDatabase attachedDatabase;
   final String? _alias;
-  $KeyValuesTable(this._db, [this._alias]);
+  $KeyValuesTable(this.attachedDatabase, [this._alias]);
   final VerificationMeta _keyMeta = const VerificationMeta('key');
   @override
   late final GeneratedColumn<String?> key = GeneratedColumn<String?>(
@@ -168,6 +169,8 @@ class $KeyValuesTable extends KeyValues
   @override
   Set<GeneratedColumn> get $primaryKey => {key};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   KeyValue map(Map<String, dynamic> data, {String? tablePrefix}) {
     return KeyValue.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -175,7 +178,7 @@ class $KeyValuesTable extends KeyValues
 
   @override
   $KeyValuesTable createAlias(String alias) {
-    return $KeyValuesTable(_db, alias);
+    return $KeyValuesTable(attachedDatabase, alias);
   }
 }
 

extras/integration_tests/tests/lib/database/database.g.dart

@@ -307,6 +307,8 @@ class $UsersTable extends Users with TableInfo<$UsersTable, User> {
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   User map(Map<String, dynamic> data, {String? tablePrefix}) {
     return User.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -531,6 +533,8 @@ class $FriendshipsTable extends Friendships
   @override
   Set<GeneratedColumn> get $primaryKey => {firstUser, secondUser};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   Friendship map(Map<String, dynamic> data, {String? tablePrefix}) {
     return Friendship.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);

extras/integration_tests/web/test/saves_after_migration_regression_test.g.dart

@@ -137,6 +137,8 @@ class $FoosTable extends Foos with TableInfo<$FoosTable, Foo> {
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   Foo map(Map<String, dynamic> data, {String tablePrefix}) {
     return Foo.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);
@@ -278,6 +280,8 @@ class $BarsTable extends Bars with TableInfo<$BarsTable, Bar> {
   @override
   Set<GeneratedColumn> get $primaryKey => {id};
   @override
+  List<Set<GeneratedColumn>> get uniqueKeys => [];
+  @override
   Bar map(Map<String, dynamic> data, {String tablePrefix}) {
     return Bar.fromData(data,
         prefix: tablePrefix != null ? '$tablePrefix.' : null);