Question

我试图在连接两个表时设置与Moor-Flutter的外键关系，但在VS Code中出现以下错误；

不能将参数类型'GeneratedIntColumn'分配给参数类型'int'。

起初我以为是因为我将自动增量字段用作外键，但是现在我不确定，因为更改代码后仍然会出现错误。

这是我的代码。比较时，该错误发生在join语句上； task.id.equals（categories.taskId）。

import 'package:moor/moor.dart';
import 'package:moor_flutter/moor_flutter.dart';

part 'moor_database.g.dart';

@DataClassName("Category")
class Categories extends Table {
  IntColumn get id => integer().autoIncrement()();
  IntColumn get taskId =>
      integer().nullable().customConstraint('NULL REFERENCES tasks(id)')();
  TextColumn get name => text().withLength(min: 1, max: 100)();
  TextColumn get icon => text()();
  TextColumn get color => text()();
}

class Tasks extends Table {
  IntColumn get id => integer().autoIncrement()();
  TextColumn get name => text().withLength(min: 1, max: 200)();
  BoolColumn get completed => boolean().withDefault(Constant(false))();
}

@UseMoor(tables: [Categories, Tasks], daos: [CategoryDao])
class AppDatabase extends _$AppDatabase {
  AppDatabase()
      : super((FlutterQueryExecutor.inDatabaseFolder(
          path: 'todo.sqlite',
          logStatements: true,
        )));

  @override
  int get schemaVersion => 1;

  @override
  MigrationStrategy get migration =>
      MigrationStrategy(beforeOpen: (details) async {
        await customStatement('PRAGMA foreign_keys = ON');
      });
}

class CategoryWithTask {
  final Category category;
  final Task task;

  CategoryWithTask({@required this.category, @required this.task});
}

@UseDao(tables: [Categories, Tasks])
class CategoryDao extends DatabaseAccessor<AppDatabase>
    with _$CategoryDaoMixin {
  final AppDatabase db;

  CategoryDao(this.db) : super(db);
  Stream<List<CategoryWithTask>> watchAllCategories() {
    return (select(categories)
          ..orderBy(([
            (c) => OrderingTerm(expression: c.name),
          ])))
        .join([leftOuterJoin(tasks, tasks.id.equals(categories.taskId))])
        .watch()
        .map((rows) => rows.map((row) {
              return CategoryWithTask(
                  category: row.readTable(categories),
                  task: row.readTable(tasks));
            }));
  }
}

Answer 1

通过查看https://resocoder.com/2019/07/17/moor-room-for-flutter-3-foreign-keys-joins-migrations-fluent-sqlite-database/

中的代码示例，我已经意识到自己的错误。

代替tasks.id.equals(categories.taskId)

联接中的表达式应为tasks.id.equalsExp(categories.taskId)

参数类型'GeneratedIntColumn'不能分配给参数类型'int'：Moor-Flutter

1 个答案: