Add `count()` as a utility extension

drift/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 2.14.0-dev
 
 - Add the `QueryInterceptor` to easily monitor all database calls made by drift.
+- Add the `count()` extension on tables to easily count rows in tables or views.
 
 ## 2.13.1
 

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

@@ -12,6 +12,23 @@ extension TableOrViewStatements<Tbl extends HasResultSet, Row>
     return select();
   }
 
+  /// Counts the rows in this table.
+  ///
+  /// The optional [where] clause can be used to only count rows matching the
+  /// condition, similar to [SimpleSelectStatement.where].
+  ///
+  /// The returned [Selectable] can be run once with [Selectable.getSingle] to
+  /// get the count once, or be watched as a stream with [Selectable.watchSingle].
+  Selectable<int> count({Expression<bool> Function(Tbl row)? where}) {
+    final count = countAll();
+    final stmt = selectOnly()..addColumns([count]);
+    if (where != null) {
+      stmt.where(where(asDslTable));
+    }
+
+    return stmt.map((row) => row.read(count)!);
+  }
+
   /// Composes a `SELECT` statement on the captured table or view.
   ///
   /// This is equivalent to calling [DatabaseConnectionUser.select].

drift/test/database/statements/select_test.dart

@@ -256,4 +256,33 @@ void main() {
       [r'$.foo'],
     ));
   });
+
+  group('count', () {
+    test('all', () async {
+      when(executor.runSelect(any, any)).thenAnswer((_) async => [
+            {'c0': 3}
+          ]);
+
+      final result = await db.todosTable.count().getSingle();
+      expect(result, 3);
+
+      verify(executor.runSelect(
+          'SELECT COUNT(*) AS "c0" FROM "todos";', argThat(isEmpty)));
+    });
+
+    test('with filter', () async {
+      when(executor.runSelect(any, any)).thenAnswer((_) async => [
+            {'c0': 2}
+          ]);
+
+      final result = await db.todosTable
+          .count(where: (row) => row.id.isBiggerThanValue(12))
+          .getSingle();
+      expect(result, 2);
+
+      verify(executor.runSelect(
+          'SELECT COUNT(*) AS "c0" FROM "todos" WHERE "todos"."id" > ?;',
+          [12]));
+    });
+  });
 }