如何检查 LinqToXML 表达式中的 null 属性？

发布于 2024-11-29 00:37:51 字数 1032 浏览 1 评论 0原文

我有一个 LinqToXML 表达式，我试图根据相似的属性选择不同的名称。代码运行良好，我将其放在下面：

            var q = xmlDoc.Element("AscentCaptureSetup").Element("FieldTypes")
            .Descendants("FieldType")
            .Select(c => new { width = c.Attribute("Width").Value,
                                script = c.Attribute("ScriptName").Value,
                                sqlType = c.Attribute("SqlType").Value,
                                enableValues = c.Attribute("EnableValues").Value,
                                scale = c.Attribute("Scale").Value,
                                forceMatch = c.Attribute("ForceMatch").Value,
                                forceMatchCaseSensitive = c.Attribute("ForceMatchCaseSensitive").Value,
                                sortAlphabetically = c.Attribute("SortAlphabetically").Value,
                            })
            .Distinct();

问题的出现是因为并非所有属性都是必需的，如果省略其中一个属性，例如 sortAlphabetically，我会收到“对象未引用”错误。有道理，但是有没有办法改变查询，仅在属性实际存在时才使用分配新值？（从而绕过任何空指针错误）

原文

I have a LinqToXML expression where I am trying to select distinct names based on similar attributes. The code is working great and I've put it below:

            var q = xmlDoc.Element("AscentCaptureSetup").Element("FieldTypes")
            .Descendants("FieldType")
            .Select(c => new { width = c.Attribute("Width").Value,
                                script = c.Attribute("ScriptName").Value,
                                sqlType = c.Attribute("SqlType").Value,
                                enableValues = c.Attribute("EnableValues").Value,
                                scale = c.Attribute("Scale").Value,
                                forceMatch = c.Attribute("ForceMatch").Value,
                                forceMatchCaseSensitive = c.Attribute("ForceMatchCaseSensitive").Value,
                                sortAlphabetically = c.Attribute("SortAlphabetically").Value,
                            })
            .Distinct();

The problem arises since not all the attributes are required, and if one of them is omitted, for example sortAlphabetically, I get an Object not Referenced error. Makes sense, but it there a way to alter the query to only use assign the new values if the attribute actually exists? (Thereby bypassing any null pointer errors)

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

携君以终年 2024-12-06 00:37:51

不要使用 Value 属性（该属性会在空引用上爆炸），只需将 XAttribute 转换为字符串 - 您将得到值，或空引用（如果XAttribute 引用为空）。（XElement 的工作方式相同，这适用于所有可空类型的转换。）

因此您会得到：

.Select(c => new { 
     width = (string) c.Attribute("Width"),
     script = (string) c.Attribute("ScriptName"),
     sqlType = (string) c.Attribute("SqlType"),
     enableValues = (string) c.Attribute("EnableValues"),
     scale = (string) c.Attribute("Scale"),
     forceMatch = (string) c.Attribute("ForceMatch"),
     forceMatchCaseSensitive = (string) c.Attribute("ForceMatchCaseSensitive"),
     sortAlphabetically = (string) c.Attribute("SortAlphabetically"),
 })

其中一些属性听起来应该实际上被转换为int? 或 bool?，请注意...

Instead of using the Value property (which will blow up on a null reference), simply cast the XAttribute to string - you'll either get the value, or a null reference if the XAttribute reference is null. (XElement works the same way, and this applies to all conversions to nullable types.)

So you'd have:

.Select(c => new { 
     width = (string) c.Attribute("Width"),
     script = (string) c.Attribute("ScriptName"),
     sqlType = (string) c.Attribute("SqlType"),
     enableValues = (string) c.Attribute("EnableValues"),
     scale = (string) c.Attribute("Scale"),
     forceMatch = (string) c.Attribute("ForceMatch"),
     forceMatchCaseSensitive = (string) c.Attribute("ForceMatchCaseSensitive"),
     sortAlphabetically = (string) c.Attribute("SortAlphabetically"),
 })

Some of those attributes sound like they should actually be cast to int? or bool?, mind you...

回复收藏 0 原文

~没有更多了~