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    import 'dart:async';

    import 'package:moor_flutter/moor_flutter.dart';

    part 'tables.g.dart';

    //Adds a Categorys table...

    class Categorys extends Table {
      IntColumn get cid => integer().named('cid').autoIncrement()();
      TextColumn get ctitle => text().named('ctitle')();
      DateTimeColumn get ctimestamp => dateTime().named('ctimestamp')();
      TextColumn get mategorymtitle =>
          text().nullable().customConstraint('NULL REFERENCES mategorys(mtitle)')();
    }

     //Adds a Mategory table...

    class Mategorys extends Table {
      //IntColumn get mid => integer().named('mid').autoIncrement()();
      TextColumn get mtitle => text().named('mtitle')();
      DateTimeColumn get mtimestamp => dateTime().named('mtimestamp')();
      //IntColumn get cid => integer().named('cid')();

      @override
      Set<Column> get primaryKey => {mtitle};
    }

    //Adds a CategorywithMategory class...

    class CategoryWithMategory {
      final Category category;
      final Mategory mategory;

      CategoryWithMategory({
        @required this.category,
        @required this.mategory,
      });
    }

    //Adds a MyDatabase class...

    @UseMoor(tables: [Categorys, Mategorys], daos: [CategorysDao, MategorysDao])
    class MyDatabase extends _$MyDatabase {
      MyDatabase()
          : super(FlutterQueryExecutor.inDatabaseFolder(
              path: 'db.sqlite',
            ));

      @override
      int get schemaVersion => 1;
    }

    //Adds a CategorysDao name...    

    @UseDao(tables: [Categorys,Mategorys])
    class CategorysDao extends DatabaseAccessor<MyDatabase>
        with _$CategorysDaoMixin {
      CategorysDao(MyDatabase db) : super(db);

      Stream<List<CategoryWithMategory>> watchAllCategorys() {
        return (select(categorys)
              ..orderBy(
                [
                  (t) => OrderingTerm(expression: t.cid, mode: OrderingMode.asc),
                  (t) => OrderingTerm(expression: t.mategorymtitle),
                ],
              ))
            .join(
              [
                leftOuterJoin(mategorys,
                    mategorys.mtitle.equalsExp(categorys.mategorymtitle)),
              ],
            )
            .watch()
            .map((rows) => rows.map(
                  (row) {
                    return CategoryWithMategory(
                      category: row.readTable(categorys),
                      mategory: row.readTable(mategorys),
                    );
                  },
                ).toList());
      }



      Future<List<Category>> get allWatchingCategorys => select(categorys).get();

      //Adds a category name...
      void addCategory({String ctitle, DateTime ctimestamp}) {
        final _entry = CategorysCompanion(
          ctitle: Value(ctitle),
          ctimestamp: Value(ctimestamp),
        );
        into(categorys).insert(_entry);
      }

      //Updates a category name...
      void updateCategory({String ctitle, DateTime ctimestamp}) {
        final _entry = CategorysCompanion(
          ctitle: Value(ctitle),
          ctimestamp: Value(ctimestamp),
        );
        update(categorys).write(_entry);
      }
    }

    //Adds a MategoryDao name...
    class MategorysDao extends DatabaseAccessor<MyDatabase>
        with _$MategorysDaoMixin {
      MategorysDao(MyDatabase db) : super(db);

      Future<List<Mategory>> get allWatchingMategorys => select(mategorys).get();
      Stream<List<Mategory>> get watchAllMategorys => select(mategorys).watch();

      //Adds a mategory name...
      void addMategory({String mtitle, DateTime mtimestamp}) {
        final _entry = MategorysCompanion(
          mtitle: Value(mtitle),
          mtimestamp: Value(mtimestamp),
        );
        into(mategorys).insert(_entry);
      }

      //Updates a mategory name...
      void updateMategory({String mtitle, DateTime mtimestamp}) {
        final _entry = MategorysCompanion(
          mtitle: Value(mtitle),
          mtimestamp: Value(mtimestamp),
        );
        update(mategorys).write(_entry);
      }
    }

**我在 android studio 的 dart 中制作了这个程序。它有两个表 Categorys 和 Mategorys。Mategorys 只不过是类别的子列表。Flutter 中的上述程序在 CatgorysDao 类中显示错误，在 watchAllCategorys 方法中的 leftouterjoin 中，由于 mategorys。无法理解为什么。请问有人能找出错误吗？我无法使用颤振中的 moor 库编写具有两个或多个表的正确程序。请帮忙...

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1 回答 1

0

您忘记在 MategorysDao 中添加表格

//Adds a MategoryDao name...
    class MategorysDao extends DatabaseAccessor<MyDatabase>
        with _$MategorysDaoMixin {}

改变这个

@UseDao(tables:[Mategory])
 class MategorysDao extends DatabaseAccessor<MyDatabase>
            with _$MategorysDaoMixin {}
于 2020-03-04T09:01:25.630 回答