This row already belongs to another table."

When you try to add a DataRow from one table to another, you may encounter the following error message:

"This row already belongs to another table."

This error message appears if you try to add (copy) a DataRow from table1 to table2, for example, with the following C# code:

table2.Rows.Add(row);

where row is a DataRow object from table1.

To successfully copy the row, you'll need to use ImportRow() method:

table2.ImportRow(row);

Don't forget to define a proper value of column number for table2 first or no data will be displayed if you bind table2 with a gridview, for example.

Customize DataRow to keep an object

To enable a DataRow to keep a custom object, create a new class inheriting DataRow class.

The code below shows how to keep an object of a custom class named "VideoGame".

 

#region Custom DataRow

pubilc class VideoGameDataRow : DataRow{

        private VideoGame vdoGame;

        public VideoGameDataRow(DataRowBuilder rowBuilder) : base(rowBuilder)

                // Default constructor.

        }

        public VideoGame GameObject{

                set { vdoGame = value; }

                get { return vdoGame; }

        }

}

#endregion

 

You will also need a custom DataTable to handle this custom DataRow since the default DataTable can take only the default DataRow.

Override the NewRow method (NewRowBuilder()) to handle the custom DataRow.

 

#region Custom DataTable

public class VideoGameTable : DataTable{

        protected override DataRow NewRowBuilder(DataRowBuilder builder){

                return new VideoGameDataRow(builder);

        }

}

#endregion

 

When used, cast a created row as the custom DataRow.

 

#region Usage

...

        VideoGame game = new VideoGame();

        VideoGameDataTable vdoGameTable = new VideoGameDataTable();

        VideoGameDataRow newGameRow = (VideoGameDataRow)(vdoGameTable.NewRow());

        newGameRow.GameObject = game;

...

#endregion

 

Note that you cannot create a new DataRow using the new keyword (DataRow row = new DataRow();).

This will generate an error saying that DataRow(DataRowBuilder) is inaccessible due to its protection level.

This applies to a custom DataRow which inherits from DataRow as well.

 

 

Reading XmlDocument which has a namespace

The scenario is I was trying to read a response message from Amazon AWS which contains a namespace using VS2008/C#.

A sample document can be found here.

Let's assume that the response message has been saved as ItemLookupResponse.xml.

I tried the following code to get the number of elements in the document.

Counted manually, the total number of elements is 10.

XmlDocument xDoc = new XmlDocument();

xDoc.Load("resources/ItemLookupResponse.xml");

XmlNodeList offerNodes = xDoc.SelectNodes("//Offer");

return offerNodes.Count;

Guess what you would get as the returned integer...

Well... I expected 10.

But it turned out to be 0!

After doing some researches, I found that

If the XML includes a default namespace, XmlNamespaceManager must be used and a prefix and namespace URI must be added to it.

Therefore, my code has been modified to be as followed:

XmlDocument xDoc = new XmlDocument();

xDoc.Load("resources/ItemLookupResponse.xml");

XmlNamespaceManager nsMgr = new XmlNamespaceManager(xDoc.NameTable);

// get the document's default namespace URI.

nsMgr.AddNamespace("aws", xDoc.DocumentElement.NamespaceURI); 

XmlNodeList offerNodes = xDoc.SelectNodes("//aws:Offer", nsMgr);

return offerNodes.Count;

Now it returns 10 as expected. Sweet~

Notice that the defined prefix is needed in the XPath expression (//aws:Offer).