Question

我正在努力解决从yahoo finance通过yql返回的股票市场数据的LINQ to XML查询问题。有些字段带有错误的数据或空值。我目前的错误是：

输入字符串的格式不正确。

我为我感兴趣的每个元素添加了一个检查空值，但错误仍然存在。

如果有帮助，看似抛出异常的突出显示的代码部分是包含我的数据点对象的“新”初始化的块。如果XML传递了查询中的检查，则在初始化DailyPricingVolDP时将空值传递给构造函数时会抛出错误。

Func<string, DateTime?> tryToGetDate =
    value =>
    {
        DateTime dateValue;
        return DateTime.TryParse(value, out dateValue)
            ? (DateTime?)dateValue
            : null;
    };

XDocument doc = XDocument.Load(addressString);
XElement results = doc.Root.Element("results");

CultureInfo enUS = new CultureInfo("en-US");
DateTime targetDate = new DateTime(2012, 1, 25);

var makeInfo =
    from s in doc.Descendants("quote")
    where s.Element("LastTradeDate") != null
       && s.Attribute("symbol") != null
    let dateStr = s.Element("LastTradeDate").Value
    let dateValue = tryToGetDate(dateStr)
    where dateValue != null && (DateTime)dateValue == targetDate
       && s.Element("Open") != null && s.Element("DaysHigh") != null
       && s.Element("DaysLow") != null && s.Element("LastTradePriceOnly") != null
       && s.Element("Volume") != null
    select new DailyPricingVolDP(
        (string)s.Attribute("symbol"),
        (DateTime)s.Element("LastTradeDate"),
        (double)s.Element("Open"),
        (double)s.Element("DaysHigh"),
        (double)s.Element("DaysLow"),
        (double)s.Element("LastTradePriceOnly"),
        (long)s.Element("Volume"));

<quote symbol="AFFM">
  <Ask>0.89</Ask>
  <AverageDailyVolume>6523</AverageDailyVolume>
  <Bid>0.67</Bid>
  <AskRealtime>0.89</AskRealtime>
  <BidRealtime>0.67</BidRealtime>
  <BookValue>4.804</BookValue>
  <Change_PercentChange>0.00 - 0.00%</Change_PercentChange>
  <Change>0.00</Change>
  <Commission />
  <ChangeRealtime>0.00</ChangeRealtime>
  <AfterHoursChangeRealtime>N/A - N/A</AfterHoursChangeRealtime>
  <DividendShare>0.00</DividendShare>
  <LastTradeDate>1/25/2012</LastTradeDate>
  <TradeDate />
  <EarningsShare>-4.491</EarningsShare>
  <ErrorIndicationreturnedforsymbolchangedinvalid />
  <EPSEstimateCurrentYear>0.00</EPSEstimateCurrentYear>
  <EPSEstimateNextYear>0.00</EPSEstimateNextYear>
  <EPSEstimateNextQuarter>0.00</EPSEstimateNextQuarter>
  <DaysLow />
  <DaysHigh />
  <YearLow>0.42</YearLow>
  <YearHigh>2.95</YearHigh>
  <HoldingsGainPercent>- - -</HoldingsGainPercent>
  <AnnualizedGain />
  <HoldingsGain />
  <HoldingsGainPercentRealtime>N/A - N/A</HoldingsGainPercentRealtime>
  <HoldingsGainRealtime />
  <MoreInfo>cnprmiIed</MoreInfo>
  <OrderBookRealtime />
  <MarketCapitalization>9.2M</MarketCapitalization>
  <MarketCapRealtime />
  <EBITDA>-34.5M</EBITDA>
  <ChangeFromYearLow>+0.18</ChangeFromYearLow>
  <PercentChangeFromYearLow>+42.86%</PercentChangeFromYearLow>
  <LastTradeRealtimeWithTime>N/A - &lt;b&gt;0.60&lt;/b&gt;</LastTradeRealtimeWithTime>
  <ChangePercentRealtime>N/A - 0.00%</ChangePercentRealtime>
  <ChangeFromYearHigh>-2.35</ChangeFromYearHigh>
  <PercebtChangeFromYearHigh>-79.66%</PercebtChangeFromYearHigh>
  <LastTradeWithTime>Jan 25 - &lt;b&gt;0.60&lt;/b&gt;</LastTradeWithTime>
  <LastTradePriceOnly>0.60</LastTradePriceOnly>
  <HighLimit />
  <LowLimit />
  <DaysRange>N/A - N/A</DaysRange>
  <DaysRangeRealtime>N/A - N/A</DaysRangeRealtime>
  <FiftydayMovingAverage>0.5639</FiftydayMovingAverage>
  <TwoHundreddayMovingAverage>1.4051</TwoHundreddayMovingAverage>
  <ChangeFromTwoHundreddayMovingAverage>-0.8051</ChangeFromTwoHundreddayMovingAverage>
  <PercentChangeFromTwoHundreddayMovingAverage>-57.30%</PercentChangeFromTwoHundreddayMovingAverage>
  <ChangeFromFiftydayMovingAverage>+0.0361</ChangeFromFiftydayMovingAverage>
  <PercentChangeFromFiftydayMovingAverage>+6.39%</PercentChangeFromFiftydayMovingAverage>
  <Name>Affirmative Insur</Name>
  <Notes />
  <Open />
  <PreviousClose>0.60</PreviousClose>
  <PricePaid />
  <ChangeinPercent>0.00%</ChangeinPercent>
  <PriceSales>0.03</PriceSales>
  <PriceBook>0.12</PriceBook>
  <ExDividendDate>12-Dec-08</ExDividendDate>
  <PERatio />
  <DividendPayDate>31-Dec-08</DividendPayDate>
  <PERatioRealtime />
  <PEGRatio />
  <PriceEPSEstimateCurrentYear />
  <PriceEPSEstimateNextYear />
  <Symbol>AFFM</Symbol>
  <SharesOwned />
  <ShortRatio>0.20</ShortRatio>
  <LastTradeTime>1:34pm</LastTradeTime>
  <TickerTrend>&amp;nbsp;======&amp;nbsp;</TickerTrend>
  <OneyrTargetPrice>6.00</OneyrTargetPrice>
  <Volume>200</Volume>
  <HoldingsValue />
  <HoldingsValueRealtime />
  <YearRange>0.42 - 2.95</YearRange>
  <DaysValueChange>- - 0.00%</DaysValueChange>
  <DaysValueChangeRealtime>N/A - N/A</DaysValueChangeRealtime>
  <StockExchange>NasdaqNM</StockExchange>
  <DividendYield />
  <PercentChange>0.00%</PercentChange>
</quote>

Answer 1

此

s.Element("Open") != null

不符合您的想法。如果有一个元素Open，即使看起来与您的示例中的相同（<Open />） - 该条件也是如此。元素Open存在，并且不为空。它只是没有值（或者确切地说，它具有空字符串，""的值 - 这会导致您的格式异常）。

在where条款中，您应该将条件更改为

s.Element("Volume").Value != ""

以防止尝试解析空值元素。

快速举例。这个小程序打印的是什么？

var xDoc = XDocument.Parse("<quote><Open /></quote>");
var open = xDoc.Descendants("quote").First().Element("Open");
Console.WriteLine(open == null);
Console.WriteLine(open);

没错。 False后跟<Open />。

Answer 2

您在查询中执行的那些空检查毫无意义，（几乎所有）这些元素都存在于XML中，但其中许多都是空的。您正在尝试解析空字符串，但未能提供错误。您应该给我们一个样本XML，它代表您实际拥有的内容（即，其中包含值）。如果这是您所拥有的，那么您正在执行错误的检查。

我已经重新构建了这样的查询，并且我已经标记了发生异常的位置：

var query =
    from quote in doc.Descendants("quote")
    let lastTradeDate = (DateTime)quote.Element("LastTradeDate")
    where lastTradeDate == targetDate
    let symbol = (string)quote.Attribute("symbol")
    let open = (double)quote.Element("Open") // EXCEPTION: empty string to a double?
    let daysHigh = (double)quote.Element("DaysHigh") // DITTO
    let daysLow = (double)quote.Element("DaysLow") // DITTO
    let lastTradePriceOnly = (double)quote.Element("LastTradePriceOnly")
    let volume = (long)quote.Element("Volume") // no Volume element exists, null check might be appropriate
    select new DailyPricingVolDP(symbol, lastTradeDate, open, daysHigh, daysLow, lastTradePriceOnly, volume);

在LINQ to XML查询中格式化错误

2 个答案: