Question

I have a DataTable which I select from database (Well, these data cross several tables, after the query and putting into a DataTable, it shows at below)

ColumnA ColumnB
a             11
b             33
b             44
a             22
b             55

but I want to transform it into an XML like this

<root>
   <header name ='a'>
       <item name='11' />
       <item name='22' />
   </header>
   <header name ='b'>
       <item name='33' />
       <item name='44' />
       <item name='55' />
   </header>

</root>

Is there an easy way to implement it by C#?

Answer 1

OK, second approach after learning that the data is available in a DataTable to begin with.

The code is a bit more involved, since based on a DataTable, you can’t really do much in terms of grouping etc. I am building up the XmlDocument (since you’re on .NET 2.0) while scanning through the rows of data. I need to keep track of the <header> elements in a dictionary, in order to add a second, third entry with the same “ColumnA” value to that already existing XmlElement in the document – it’s a bit involved, but if you study it carefully, I hope you see it’s really no trickery or anything – just a bit of bookkeeping along the way of building the XmlDocument:

// create the XmlDocument and add <root> node
XmlDocument doc = new XmlDocument();
doc.AppendChild(doc.CreateElement("root"));

// dictionary to keep track of <header> nodes
Dictionary<string, XmlNode> nodesPerColumnA = new Dictionary<string, XmlNode>();

// Loop through data rows
foreach (DataRow row in tbl.Rows)
{
   // extract values for ColumnA and ColumnB as strings
   string columnAValue = row["ColumnA"].ToString();
   string columnBValue = row["ColumnB"].ToString();

   // create a new <item> XmlNode and fill its attribute @Name 
   XmlElement newNode = doc.CreateElement("item");

   XmlAttribute newNodeAttribute = doc.CreateAttribute("name");
   newNodeAttribute.InnerText = columnBValue;

   newNode.Attributes.Append(newNodeAttribute);

   // check if we already have a <header> node for that "ColumnA" value
   if(nodesPerColumnA.ContainsKey(columnAValue))
   {
       // if so - just add <item> below that <header>
       XmlNode parent = nodesPerColumnA[columnAValue];

       parent.AppendChild(newNode);
   }
   else
   {
       // if not - create appropriate <header> node and its @name attribute
       XmlElement header = doc.CreateElement("header");

       XmlAttribute headerAttr = doc.CreateAttribute("name");
       headerAttr.InnerText = columnAValue;

       header.Attributes.Append(headerAttr);

       header.AppendChild(newNode);

       doc.DocumentElement.AppendChild(header);

       // store that <header> xmlnode into the dictionary for future use
       nodesPerColumnA.Add(columnAValue, header);
    }
 }

 // check the contents of the XmlDocument at the end
 string xmlContents = doc.InnerXml;