使用flutter的sqflite

问题描述

我尝试使用sqflite保存一些数据，例如我的电影类，但是当我尝试在数据库中插入或查询时，请看到此消息：

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

我的MovieBloc班：

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MovieProvider班：

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;
  }
}

我使用save的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;
  }

我来自sqflite的load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，在insertAll类的MovieProvider方法中，将movies列表中的任何电影插入带有等待和异步的sq：

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

我尝试使用close和open数据库close和open数据库有时是顺序播放和其他游戏...

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)

请帮助我修复它

解决方法

打开/关闭数据库非常困难。确实，在很多情况下，您可能会访问关闭的数据库，甚至更糟的是，如果您打开同一数据库两次，则会得到相同的实例，因此第一次关闭将关闭该数据库。

我个人建议保持数据库打开。

如果需要处理多个数据库并为短期操作而打开/关闭它们，请确保具有适当的互斥锁/锁定机制，以便控制如何打开/访问/关闭数据库，而无需任何其他方法尝试访问数据库。同时使用相同的数据库（确定这一部分还不清楚，对不起）。

类似的事情（尽管我确实不建议每次都打开/关闭）：

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
    };
  });
}

当您关闭数据库时，您需要为您的数据库实例设置 null。否则它将始终返回旧实例。

127.0.0.1:6379> set test_key 'Test Value'
127.0.0.1:6379> get test_key
"Test Value"

}

dart sqflite sqlite