Today one of my colleague got this problem while copying datarow from one table to another, he just want to update few values of a same schema dataTable. So he used following method.

for (var i = 0; i < 10; i++)
{
	var row = dataTable.NewRow();
	row[0] = i.ToString();
	dataTable.Rows.Add(row);
}

for (int i = 0; i < 10; i++)
{
	var dr = dataTable.Rows[i];
	dr[0] = (i + 10).ToString();
	//This line throws exception
	dataTable1.Rows.Add(dr);
}

He was getting an exception like “This row already belongs to another table”. This exception is coming because of A DataRow can only belong to a single data table.

ArgumentException – This row already belongs to another table

I got this exception many times (in good(?) old ASP.Net 1.1 days ) and able to fix, but today I couldn’t remember the solution. Later we fixed it, and here is the solutions.

1. Using Item array property : Instead of using the row directly from other second table, use the ItemArray property.

   var dr = dataTable.Rows[i].ItemArray;
   dr[0] = (i + 10).ToString();
   dataTable.Rows.Add(dr);
   

2. Using DataTable.Clone() and ImportRow() methods : Instead of using creating a new DataTable with same schema again, clone the DataTable and using ImportRow method.

   DataTable dataTable1 = dataTable.Clone();
   var dr = dataTable.Rows[i];
   dr[0] = (i + 10).ToString();
   dataTable1.ImportRow(dr);
   

Happy coding and Thanks to Sarath