Question

我的未来是sql查询的结果，在其中我循环每个返回的行，将其添加到带有地图的列表中，以便稍后将其编码为json格式。在这个循环中，我根据外部查询的每一行中的结果执行另一个查询，并将这些行再次添加到地图中。

Future<Results> mysqlAllTags = mysqlCon.query(query).then((results){
  // Make new list as a part of the JsonObject
  json.tags = new List();
  // Loop throught the row of the result from Mysql data
  return results.forEach((row){
    // Create Map to put the word, value, rating and id into the JsonObject
    Map data = new Map();

    // Put the Mysql data into the Map
    data["word"] = row.word.toString();
    data["value"] = row.value.toString();
    data["rating"] = row.rating.toString();
    data["id_tag"] = row.id_tag.toString();
    data["replacing"] = null;

    // Add the Map to the userPages list
    json.tags.add(data);
  }).then((e){
    for(var tag in json.tags){
      //Map dataReplacing = getReplacing(userId, row.id_tag.toString());
      String replacingTags = getReplacingSQL(tag['id_tag'].toString());
      mysqlCon.query(replacingTags).then((result){
        result.forEach((row1){
          Map map = new Map();

          map["word"] = row1.word.toString();
          map["value"] = row1.value.toString();
          map["id_tag"] = row1.id_replacing_tag.toString();
          tag["replacing"] = map;
        }).then((e){
          print("then inner for called");
          return null;
        });
        print("then inner for called");
        return null;
      });
    }

    print("outer for returned");
    // Send the data in UTF8 to the client 
    result = Helpers.formatJsonAndEncodeUtf8('OK', session:_session, data: [json]);

    return null;
  }).catchError((error){
     result = Helpers.formatJsonAndEncodeUtf8('ERROR 856284555 (Could not load tags)', session:_session);
  });
}).catchError((error){
  result = Helpers.formatJsonAndEncodeUtf8('ERROR 2346644555 (Could not load tags)', session:_session);
});

return Future.wait([mysqlAllTags]).then((e){
  print("future returned");
  return result;
});

结果如下：

返回外部

=== TO CLIENT ===

{＆＃34;状态＆＃34;：[{＆＃34;消息＆＃34;：＆＃34; OK＆＃34;＆＃34; csrfToken＆＃34;：＆＃34; 99＆＃34; }]，＆＃34;数据＆＃34;：[{＆＃34;标记＆＃34;：[{＆＃34;字＆＃34;：＆＃34;甜瓜＆＃34;＆＃34;值＆＃34 ;：＆＃34; 11.0＆＃34;＆＃34;评价＆＃34;：＆＃34; 1＆＃34;＆＃34; id_tag＆＃34;：＆＃34; 37＆＃34;＆＃ 34;替换＆＃34;：空}，........}]}

=================

未来回归

然后内部称为

然后内部称为

然后内部称为

然后内部称为

然后内部称为

然后内部称为

然后内部称为

然后内部称为

我怎么能等到for循环中的所有期货都完成？

Answer 1

我通过在Future.wait(futures).then()函数中添加结果声明来解决它。感谢GünterZöchbauer的意见。

Future<Results> mysqlAllTags = mysqlCon.query(query).then((results){
  // Make new list as a part of the JsonObject
  json.tags = new List();
  // Loop throught the row of the result from Mysql data
  return results.forEach((row){
  // Create Map to put the word, value, rating and id into the JsonObject
  Map data = new Map();

  // Put the Mysql data into the Map
  data["word"] = row.word.toString();
  data["value"] = row.value.toString();
  data["rating"] = row.rating.toString();
  data["id_tag"] = row.id_tag.toString();
  data["replacing"] = null;

  // Add the Map to the userPages list
  json.tags.add(data);
}).then((e){
  var futures = []; // added
  for(var tag in json.tags){
    print("row ");
    print(json.tags);
    //Map dataReplacing = getReplacing(userId, row.id_tag.toString());
    String replacingTags = getReplacingSQL(tag['id_tag'].toString());

    // added `futures.add(...)`
    futures.add(mysqlCon.query(replacingTags).then((result) { 
      result.forEach((row1){
        Map map = new Map();

        map["word"] = row1.word.toString();
        map["value"] = row1.value.toString();
        map["id_tag"] = row1.id_replacing_tag.toString();
        tag["replacing"] = map;
      }).then((e){
        print("then inner for called");
        return null;
      });
      print("then inner for called");
      return null;
    }));
  }

  print("outer for returned");
  // Send the data in UTF8 to the client 

    return Future.wait(futures).then((e){
      result = Helpers.formatJsonAndEncodeUtf8('OK', session:_session, data: [json]);
    }); // added
  }).catchError((error){
     result = Helpers.formatJsonAndEncodeUtf8('ERROR 856284555 (Could not load tags)', session:_session);
  });
}).catchError((error){
  result = Helpers.formatJsonAndEncodeUtf8('ERROR 2346644555 (Could not load tags)', session:_session);
});

return Future.wait([mysqlAllTags]).then((e){
  print("future returned");
  return result;
});

Answer 2

我不确定这是否解决了所有问题，在这样的代码中不容易看到究竟是什么导致了未来。（我在添加内容的地方添加了评论）

healthkit.com/api/v1/user/GetWeight

等待Future for for循环

2 个答案: