Question

How do I consume my WordPress blog’s RSS feed to display my latest blog posts on my homepage? I ran into the following piece of code to do this:

  Function GetRSSFeed(strURL as String) as DataTable
    'Get the XML data
    Dim reader as XmlTextReader = New XmlTextReader(strURL)

    'return a new DataSet
    Dim ds as DataSet = New DataSet()
    ds.ReadXml(reader)    
    Return ds.Tables(2)
  End Function

But it errors out at this line: ‘ds.ReadXml(reader)’ with the following error:

A column named 'comments' already belongs to this DataTable.

Perhaps it doesn’t work since this code is from 2003? Does anyone have a working code sample? Many thanks in advance!

Answer 1

You can use LINQ to XML to read a WordPress RSS feed.

First get the feed. Make a Uri instance out of it.

var rssFeed = new Uri("https://github.com/geersch/feed/");

Then perform a GET request.

var request = (HttpWebRequest) WebRequest.Create(rssFeed);
request.Method = "GET";
var response = (HttpWebResponse) request.GetResponse();

Get the response stream and read it to download the contents of the feed.

using (var reader = new StreamReader(response.GetResponseStream()))
{
    var feedContents = reader.ReadToEnd();
    //...
}

Still within the above using statement use LINQ to XML to parse the downloaded content and extract the information you need.

var document = XDocument.Parse(feedContents);

var posts = (from p in document.Descendants("item")
             select new
             {
                 Title = p.Element("title").Value,
                 Link = p.Element("link").Value,
                 Comments = p.Element("comments").Value,
                 PubDate = DateTime.Parse(p.Element("pubDate").Value)
             }).ToList();

Now you can iterate over the results.

foreach(var post in posts)
{
    Console.WriteLine(post.Title);
    Console.WriteLine(post.Link);
    Console.WriteLine(post.Comments);
    Console.WriteLine(post.PubDate);
}

Here I just used an anonymous type to capture the output in, but feel free to create your own BlogPost class or something similar which you can use in the LINQ query.

I’m used to C#, so that’s why I’ve used it in my reply. But you can easily convert it. There are some online converters which you can use.

Regarding your issue with the DataSet (which I personally would not use to implement this), it is caused by an item (blog post) having nodes with the same name.

For example:

<comments>...</comments>
<slash:comments>5</slash:comments>

Sure the second one has a different namespace (slash), but DataSet’s ReadXml(…) method does not care about namespaces. It tries to create a second column named "comments". That is why you get the exception.

You can still use a DataSet / DataTable if you want to. Just extract the data from the feed using LINQ to XML as shown above.

Then create a DataSet and add a new table to it.

var dataSet = new DataSet();
var blog = new DataTable("Blog");
blog.Columns.Add("Title", typeof(string));
blog.Columns.Add("Link", typeof(string));
blog.Columns.Add("Comments", typeof(string));
dataSet.Tables.Add(blog);

Iterate over the extracted data and add it to the DataTable:

foreach (var post in posts)
{
    var newRow = blog.NewRow();
    newRow["Title"] = post.Title;
    newRow["Link"] = post.Link;
    newRow["Comments"] = post.Comments;

    blog.Rows.Add(newRow);
 }

Voila, we’ve now fixed your issue by no longer relying on the DataSet’s ReadXml(…) method. Download the feed, extract the data you are interested in and persist it.