Throw from TypedResult.read/readTable if there's no data

moor/CHANGELOG.md

@@ -5,6 +5,8 @@
 - __Breaking__: Removed `QueryEngine`, its methods have been moved to `DatabaseConnectionUser`
 - __Breaking__: Changed the `args` parameter in `QueryExecutor` methods to `List<Object?>`
 - __Breaking__: Removed the second type parameter from `TypedResult.read`
+- __Breaking__: `TypedResult.read` and `TypedResult.readTable` now throw if the row does not contain
+  the requested table or expression (they used to return `null`).
 - __Breaking__: `MoorWebStorage.indexedDbIfSupported` now returns a future
 - Support null safety
 - Changed the sql representation of text types from `VARCHAR` to `TEXT`

moor/lib/src/runtime/query_builder/statements/select/select.dart

@@ -126,27 +126,51 @@ String _beginOfSelect(bool distinct) {
 /// multiple entities.
 class TypedResult {
   /// Creates the result from the parsed table data.
-  TypedResult(this._parsedData, this.rawData, [this._parsedExpressions]);
+  TypedResult(this._parsedData, this.rawData,
+      [this._parsedExpressions = const {}]);
 
   final Map<TableInfo, dynamic> _parsedData;
-  final Map<Expression, dynamic>? _parsedExpressions;
+  final Map<Expression, dynamic> _parsedExpressions;
 
   /// The raw data contained in this row.
   final QueryRow rawData;
 
   /// Reads all data that belongs to the given [table] from this row.
+  ///
+  /// If this row does not contain non-null columns of the [table], this method
+  /// will throw an [ArgumentError]. Use [readTableOrNull] for nullable tables.
   D readTable<T extends Table, D extends DataClass>(TableInfo<T, D> table) {
+    if (!_parsedData.containsKey(table)) {
+      throw ArgumentError(
+          'Invalid table passed to readTable: ${table.tableName}. This row '
+          'does not contain values for that table.');
+    }
+
     return _parsedData[table] as D;
   }
 
+  /// Reads all data that belongs to the given [table] from this row.
+  ///
+  /// Returns `null` if this row does not contain non-null values of the
+  /// [table].
+  ///
+  /// See also: [readTable], which throws instead of returning `null`.
+  D? readTableOrNull<T extends Table, D extends DataClass>(
+      TableInfo<T, D> table) {
+    return _parsedData[table] as D?;
+  }
+
   /// Reads a single column from an [expr]. The expression must have been added
   /// as a column, for instance via [JoinedSelectStatement.addColumns].
   ///
   /// To access the underlying columns directly, use [rawData].
-  D? read<D>(Expression<D> expr) {
-    if (_parsedExpressions != null) {
-      return _parsedExpressions![expr] as D;
+  D read<D>(Expression<D> expr) {
+    if (_parsedExpressions.containsKey(expr)) {
+      return _parsedExpressions[expr] as D;
     }
-    return null;
+
+    throw ArgumentError(
+        'Invalid call to read(): $expr. This result set does not have a column '
+        'for that expression.');
   }
 }

moor/lib/src/runtime/query_builder/statements/select/select_with_join.dart

@@ -212,8 +212,6 @@ class JoinedSelectStatement<FirstT extends Table, FirstD extends DataClass>
         // if all columns of this table are null, skip the table
         if (table.$columns.any((c) => row[prefix + c.$name] != null)) {
           readTables[table] = table.map(row, tablePrefix: table.$tableName);
-        } else {
-          readTables[table] = null;
         }
       }
 

moor/test/join_test.dart

@@ -1,4 +1,3 @@
-//@dart=2.9
 import 'package:mockito/mockito.dart';
 import 'package:moor/moor.dart' hide isNull;
 import 'package:test/test.dart';
@@ -6,8 +5,8 @@ import 'data/tables/todos.dart';
 import 'data/utils/mocks.dart';
 
 void main() {
-  TodoDb db;
-  MockExecutor executor;
+  late TodoDb db;
+  late MockExecutor executor;
 
   setUp(() {
     executor = MockExecutor();
@@ -80,7 +79,7 @@ void main() {
     verify(executor.runSelect(argThat(contains('DISTINCT')), any));
   });
 
-  test('reports null when no data is available', () async {
+  test('throws when no data is available', () async {
     when(executor.runSelect(any, any)).thenAnswer((_) {
       return Future.value([
         {
@@ -101,7 +100,7 @@ void main() {
     expect(result, hasLength(1));
 
     final row = result.single;
-    expect(row.readTable(db.categories), null);
+    expect(() => row.readTable(db.categories), throwsArgumentError);
     expect(
         row.readTable(db.todosTable),
         TodoEntry(
@@ -258,7 +257,7 @@ void main() {
         'GROUP BY c.id HAVING COUNT(t.id) >= ?;',
         [10]));
 
-    expect(result.readTable(todos), isNull);
+    expect(result.readTableOrNull(todos), isNull);
     expect(
       result.readTable(categories),
       Category(
@@ -272,20 +271,27 @@ void main() {
 
   test('selectWithoutResults', () async {
     final avgLength = db.todosTable.content.length.avg();
-    final query = db.selectOnly(db.todosTable)..addColumns([avgLength]);
+    final maxLength = db.todosTable.content.length.max();
+    final minLength = db.todosTable.content.length.min();
+    final query = db.selectOnly(db.todosTable)
+      ..addColumns([avgLength, maxLength]);
 
     when(executor.runSelect(any, any)).thenAnswer((_) async {
       return [
-        {'c0': 3.0}
+        {'c0': 3.0, 'c1': null},
       ];
     });
 
-    final result = await query.map((row) => row.read(avgLength)).getSingle();
+    final row = await query.getSingle();
 
     verify(executor.runSelect(
-        'SELECT AVG(LENGTH(todos.content)) AS "c0" FROM todos;', []));
+        'SELECT AVG(LENGTH(todos.content)) AS "c0", '
+        'MAX(LENGTH(todos.content)) AS "c1" FROM todos;',
+        []));
 
-    expect(result, 3.0);
+    expect(row.read(avgLength), 3.0);
+    expect(row.read(maxLength), isNull);
+    expect(() => row.read(minLength), throwsArgumentError);
   });
 
   test('join on JoinedSelectStatement', () async {

moor/test/select_test.dart

@@ -1,4 +1,3 @@
-//@dart=2.9
 import 'dart:async';
 
 import 'package:mockito/mockito.dart';
@@ -23,8 +22,8 @@ final _todoEntry = TodoEntry(
 );
 
 void main() {
-  TodoDb db;
-  MockExecutor executor;
+  late TodoDb db;
+  late MockExecutor executor;
 
   setUp(() {
     executor = MockExecutor();