c# LINQ to XML Query Expression for elemennt exhist ?

Question

<channel>
        <title>Best Web Gallery - Flash + CSS Gallery</title>
        <link>http://bestwebgallery.com&lt;/link&gt;
        <description>Featuring the world best web design</description>
        <pubDate>09 Dec 2009</pubDate>    
        <generator>http://wordpress.org/?v=2.3.2&lt;/generator&gt;
        <language>en</language>
</channel>   


<channel>
        <title>Best Web Gallery - Flash + CSS Gallery</title>
        <link>http://bestwebgallery.com&lt;/link&gt;
        <description>Featuring the world best web design</description>

            // pubDate missing

        <generator>http://wordpress.org/?v=2.3.2&lt;/generator&gt;
        <language>en</language>
</channel>




   XDocument rssFeed = XDocument.Load(url);

                    var feedResources = from details in rssFeed.Descendants("channel")
                                    select new feedResource
                                    {
                                         Title = details.Element("title").Value,
                                         Host = details.Element("link").Value,
                                         Description = details.Element("description").Value,  

                                         PublishedOn = DateTime.Parse(details.Element("pubDate").Value), 
                                         Generator = details.Element("generator").Value,
                                         Language = details.Element("language").Value
                                    };

How can We check here before trying to get Element "pubDate " or others, because if not checked, throws null reference exception ??

Answer 1

My personal preference is to add two extension methods to XElement:

public static string ValueOrDefault(this XElement xml)
{
    if (xml == null) return null;   // or String.Empty, if you prefer
    return xml.Value
}

public static string ValueOrDefault(this XElement xml, string defaultValue)
{
    if (xml == null) return defaultValue;
    return xml.Value
}

Now your code will look something like:

select new feedResource
{
     Title = details.Element("title").ValueOrDefault(),
     Host = details.Element("link").ValueOrDefault(),
     Description = details.Element("description").ValueOrDefault(),  

     PublishedOn = DateTime.Parse(details.Element("pubDate").ValueOrDefault(DateTime.Now.ToString())), 
     Generator = details.Element("generator").ValueOrDefault(),
     Language = details.Element("language").ValueOrDefault()
};

Answer 2

Don't use Parse etc; xml typically uses different string representations than it accepts; just cast (note no .Value):

select new FeedResource
{
    Title = (string)details.Element("title"),
    Host = (string)details.Element("link"),
    Description = (string)details.Element("description"),
    PublishedOn = (DateTime?)details.Element("pubDate"),
    Generator = (string)details.Element("generator"),
    Language = (string)details.Element("language")
}

XElement has conversion operators to do all the work, returning appropriate values.

Answer 3

Just change the line:

PublishedOn = DateTime.Parse(details.Element("pubDate").Value),

for:

PublishedOn = details.Element("pubDate") != null? DateTime.Parse(details.Element("pubDate").Value) : DateTime.Now,

you can change the DateTime.Now for whatever you want