使用flutter的sqflite时报错database_closed

Question

我尝试使用 sqflite 保存一些数据，例如我的 class 电影，但是当我尝试插入或查询数据库时，看到这条消息：

[ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: DatabaseException(error database_closed)

我的MovieBlocclass:

List<Movie> _movies = new List<Movie> ();
class MoviesBloc implements BaseBloc {
  final  _moviesController = StreamController<List<Movie>>();
  Database moviesDB;
  String _moviesPath;
  Stream<List<Movie>> get moviesStream => _moviesController.stream;
  List<Movie> get movies => _movies;

  int getLengthMovieList() {
    return _movies.length;
  }
  clearMovieList() {
    _movies.clear();
  }

  Future<void> openMovieDB({String dbName:'movies.db'}) async {

    var databasesPath = await getDatabasesPath();
    _moviesPath = join(databasesPath, dbName);

    moviesDB = await openDatabase(_moviesPath, version: 1,
        onCreate: (Database db, int version) async {
          await db.execute(
              'CREATE TABLE movies (Id INTEGER PRIMARY KEY AUTOINCREMENT, Title TEXT NOT NULL, imdbRating TEXT, Poster TEXT, Plot TEXT, Saved INTEGER DEFAULT 0)');
        });
  }
  Future<void> closeMovieDB() async => moviesDB.close();

  void dispose() {
    _moviesController.close();
  }
}

我的MovieProviderclass:

class MovieProvider extends MoviesBloc {
  String _tableName = 'movies';

  Future<Movie> insert(Movie movie, {conflictAlgorithm: ConflictAlgorithm.ignore}) async {
    await moviesDB.insert(_tableName, movie.toMap(), conflictAlgorithm: conflictAlgorithm);
    return movie;
  }

  Future<bool> insertAll(List<Movie> movies) async {
    await Future.wait(movies.map((movie) async {
      await this.insert(movie);
    }
    ));
    return true;
  }

  Future<List<Movie>> paginate(int page, {int limit: 15}) async {
    print('in Paginate to SQLite');
    List<Map> maps  = await moviesDB.query(_tableName,
        columns: ['Id', 'Title', 'imdbRating', 'Poster', 'Plot', 'Saved'],
        limit: limit,
        offset: page == 1 ? 0 : ((page -1) * limit)
    );
    List<Movie> movies = new List<Movie> ();
      if (maps.length > 0) {
        maps.map((movie) {
          movies.add(Movie.fromJson(movie));
        }
        );
      }
    return movies;
  }
}

我的 save sqflite 方法：

static Future<bool> saveAllMoviesIntoSqlite(List<Movie> movies) async {
    var db = new MovieProvider();
    await db.openMovieDB();
    await db.insertAll(movies);
    await db.closeMovieDB();
    return true;
  }

我的 load 来自 sqflite 的方法：

 static Future<Map> getAllMoviesFromSqlite(int page) async {
    var db = new MovieProvider();
    await db.openMovieDB();
    List<Movie> movies = new List<Movie> ();
    movies = await db.paginate(page);
    await db.closeMovieDB();
    return {
      "currentPage": page,
      "movies": movies
    };
  }

我观察到 insertAll 方法 MovieProvider class 用于将 movies 列表中的任何电影插入带有 await 和 async 的 sq:

 Future<bool> insertAll(List<Movie> movies) async {
    await Future.wait(movies.map((movie) async {
      await this.insert(movie);
    }
    ));
    return true;
  }

我尝试 close 和 open 数据库有时顺序和其他播放 close 和 open 数据库 ...

我的日志：

I/flutter ( 1617): in Paginate to SQLite
E/flutter ( 1617): [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: DatabaseException(error database_closed)
E/flutter ( 1617): #0      SqfliteDatabaseMixin.checkNotClosed (package:sqflite_common/src/database_mixin.dart:282:7)
E/flutter ( 1617): #1      SqfliteDatabaseExecutorMixin._rawQuery (package:sqflite_common/src/database_mixin.dart:125:8)
E/flutter ( 1617): #2      SqfliteDatabaseExecutorMixin.query (package:sqflite_common/src/database_mixin.dart:110:12)
E/flutter ( 1617): #3      MovieProvider.paginate (package:umdb/bloc/movie_provider.dart:24:38)
E/flutter ( 1617): #4      MovieService.getAllMoviesFromSqlite (package:umdb/services/movie_service.dart:54:23)
E/flutter ( 1617): <asynchronous suspension>
E/flutter ( 1617): #5      MovieService.getSavedFromSQ (package:umdb/services/movie_service.dart:95:26)
E/flutter ( 1617): #6      MovieService.fetchSavedMovies (package:umdb/services/movie_service.dart:105:5)
E/flutter ( 1617): <asynchronous suspension>
E/flutter ( 1617): #7      MovieDetailState.build.<anonymous closure>.<anonymous closure> (package:umdb/ui_widgets/movie_detail.dart:168:42)
E/flutter ( 1617): #8      State.setState (package:flutter/src/widgets/framework.dart:1240:30)
E/flutter ( 1617): #9      MovieDetailState.build.<anonymous closure> (package:umdb/ui_widgets/movie_detail.dart:142:27)
E/flutter ( 1617): #10     GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:184:24)
E/flutter ( 1617): #11     TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:524:11)
E/flutter ( 1617): #12     BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:284:5)
E/flutter ( 1617): #13     BaseTapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:256:7)
E/flutter ( 1617): #14     GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:158:27)
E/flutter ( 1617): #15     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:224:20)
E/flutter ( 1617): #16     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:200:22)
E/flutter ( 1617): #17     GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:158:7)
E/flutter ( 1617): #18     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:104:7)
E/flutter ( 1617): #19     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:88:7)
E/flutter ( 1617): #20     _rootRunUnary (dart:async/zone.dart:1206:13)
E/flutter ( 1617): #21     _CustomZone.runUnary (dart:async/zone.dart:1100:19)
E/flutter ( 1617): #22     _CustomZone.runUnaryGuarded (dart:async/zone.dart:1005:7)
E/flutter ( 1617): #23     _invoke1 (dart:ui/hooks.dart:267:10)
E/flutter ( 1617): #24     _dispatchPointerDataPacket (dart:ui/hooks.dart:176:5)

请帮我解决一下

Answer 1

处理opening/closing数据库非常困难。确实有很多情况你可能会访问一个关闭的数据库，更糟糕的是，如果你打开同一个数据库两次，你得到的是同一个实例，所以第一次关闭将关闭数据库。

我个人建议保持数据库打开。

如果您需要处理多个数据库并且 open/close 它们用于短期操作，请确保您拥有适当的 mutex/lock 机制，以便您可以控制数据库的方式 opened/accessed/closed 而无需任何操作尝试同时访问同一个数据库的其他方法（好的，那部分不清楚抱歉）。

类似的东西（虽然我真的不推荐每次都opening/closing）：

import 'package:synchronized/synchronized.dart';

final static _lock = Lock();

static Future<bool> saveAllMoviesIntoSqlite(List<Movie> movies) async {
  return _lock.synchronized(() {
    var db = new MovieProvider();
    await db.openMovieDB();
    await db.insertAll(movies);
    await db.closeMovieDB();
    return true;
  });
}

static Future<Map> getAllMoviesFromSqlite(int page) async {
  return _lock.synchronized(() {
    var db = new MovieProvider();
    await db.openMovieDB();
    List<Movie> movies = new List<Movie> ();
    movies = await db.paginate(page);
    await db.closeMovieDB();
    return {
      "currentPage": page,
      "movies": movies
    };
  });
}

Answer 2

您需要在关闭数据库时为您的数据库实例设置空值。否则它将始终 return 旧实例。

Future close() async {
    final db = await instance.database;
    _database = null;
    return db.close();
}

使用flutter的sqflite时报错database_closed

Error database_closed when using flutter's sqflite

sqlite

database-caching

dart

flutter

sqflite