mongodb - 更新到r16761时遇到的麻烦

Question

我已经开发了使用Mongo Dart和Future的功能。当我使用Dart SDK 0.2.9执行它时，它没有异常(exception)。

import 'model.dart';
import 'dart:json';
import 'package:mongo_dart/mongo_dart.dart';

class LinkDAO {
  DbCollection _links;

  Future<List> getAllLinks(){
    var completer = new Completer<List>();
    Db db = new Db("mongodb://127.0.0.1:27017/dart-link");
    List linkList = new List();
    _links = db.collection("links");
    db.open().chain((c){
      return _links.find({}).each(
          (link){ 
            print("[${link['link']}]:[${link['readed']}]:[${link['title']}]");
            linkList.add(new Link(link['link'],link['title'],link['readed']));
            print('lenght ${linkList.length}'); 
          }).chain((link)=>completer.complete(linkList));
     }).then((dummy){
      db.close();
    });
    return completer.future;
  }
}

void main(){
  Future<List> futureResult=new LinkDAO().getAllLinks();
  futureResult.then((result){
    print("final!!! -> ${result.length}");
  });
}

这是链接类

library models;

class Link {
  String title;
  String link;
  bool readed;
  Link(this.title,this.link,this.readed);
}

在更新到版本0.2.10之后，相同的函数会生成此异常:

[assas]:[true]:[sasas]
lenght 1
[assas]:[true]:[sasas]
lenght 2
final!!! -> 2
Unhandled exception:
NoSuchMethodError : method not found: 'handleException'
Receiver: null
Arguments: [Closure: _FutureImpl@0x36924d72<T>(dynamic, dynamic) => dynamic]
#0      Object._noSuchMethod (dart:core-patch:1360:3)
#1      Object.noSuchMethod (dart:core-patch:1361:25)
#2      _FutureImpl._forwardException (bootstrap:935:27)
#3      _FutureImpl._forward (bootstrap:931:22)
#4      _FutureImpl.chain.<anonymous closure> (bootstrap:903:15)
#5      _FutureImpl._complete (bootstrap:840:19)
#6      _FutureImpl._complete (bootstrap:848:5)
#7      _FutureImpl._setValue (bootstrap:862:14)
#8      _CompleterImpl.complete (bootstrap:949:26)
#9      Cursor._nextEach.<anonymous closure>         (package:mongo_dart/src/database/cursor.dart:112:30)
#10     _FutureImpl.then (bootstrap:792:16)
#11     Cursor._nextEach (package:mongo_dart/src/database/cursor.dart:109:22)
#12     Cursor._nextEach.<anonymous closure> (package:mongo_dart/src/database/cursor.dart:115:18)
#13     _FutureImpl.then (bootstrap:792:16)
#14     Cursor._nextEach (package:mongo_dart/src/database/cursor.dart:109:22)
#15     Cursor._nextEach.<anonymous closure> (package:mongo_dart/src/database/cursor.dart:115:18)
#16     _FutureImpl._complete (bootstrap:840:19)
#17     _FutureImpl._complete (bootstrap:848:5)
#18     _FutureImpl._setValue (bootstrap:862:14)
#19     _CompleterImpl.complete (bootstrap:949:26)
#20     Cursor.nextObject.<anonymous closure> (package:mongo_dart/src/database/cursor.dart:74:28)
#21     _FutureImpl._complete (bootstrap:840:19)
#22     _FutureImpl._complete (bootstrap:848:5)
#23     _FutureImpl._setValue (bootstrap:862:14)
#24     _CompleterImpl.complete (bootstrap:949:26)
#25     Connection._receiveData._receiveData (package:mongo_dart/src/database/connection.dart:84:27)
#26     _SocketBase._multiplex (dart:io-patch:410:26)
#27     _SocketBase._sendToEventHandler.<anonymous closure> (dart:io-patch:512:20)
#28     _ReceivePortImpl._handleMessage (dart:isolate-patch:40:92)

我认为问题出在Mogo Dart库上，但我不确定。有人可以帮助我吗？

Answer 1

看一下这一行:

chain((link)=>completer.complete(linkList));

Future.chain需要一个转换函数，该函数返回 Future，但您将传递给它的函数返回 void( null)。尝试将错误转发到此 NoSuchMethodError中时，抛出 null异常。

我认为您在这里需要 then而不是 chain。