How to Compare two DataTables in ADO.net

Sometimes it’s very useful to compare two DataTables and return the different records to a third DataTable. I came across this when I needed to handle my own data concurrency control. Basically my logic is:

- Populate a DataTable of a DataSet and Copy the content of the DataTable to another DataTable immediately after this. (For example we populate a DataTable A and then make a copy to DataTable B.)
- When user update the DataTable A in my application, the event handler firstly populate to a DataTable C from the database.
- Comparing the DataTable C with the DataTable B, if they are same means underlying data hasn’t been changed, then proceed the update otherwise user can choose either to overwrite the data or cancel the operation.

Unfortunately you can’t do a straight comparison of two DataTables. For instance if you write something like: DataTable 1 == DataTable2 or DataTable1.GetHashCode() == DataTable2..GetHashCode() or DT1.Equals(DT2), none of this would work. Below is the code I am using to compare to DataTables, pretty self-explanatory. Hopefully you find it helpful.

private void button1_Click(object sender, EventArgs e)   
{   
    // Something to do with the Initialization of the FirstDataTable and SecondDataTable   

     DataTable dt;   
     dt = getDifferentRecords(FirstDataTable, SecondDataTable);   

     if (dt.Rows.Count == 0)   
         MessageBox.Show("Equal");   
     else  
         MessageBox.Show("Not Equal");   
}

#region Compare two DataTables and return a DataTable with DifferentRecords   
 public DataTable getDifferentRecords(DataTable FirstDataTable, DataTable SecondDataTable)   
 {   
     //Create Empty Table   
     DataTable ResultDataTable = new DataTable("ResultDataTable");   

     //use a Dataset to make use of a DataRelation object   
     using (DataSet ds = new DataSet())   
     {   
         //Add tables   
         ds.Tables.AddRange(new DataTable[] { FirstDataTable.Copy(), SecondDataTable.Copy() });   

         //Get Columns for DataRelation   
         DataColumn[] firstColumns = new DataColumn[ds.Tables[0].Columns.Count];   
         for (int i = 0; i < firstColumns.Length; i++)   
         {   
            firstColumns[i] = ds.Tables[0].Columns[i];   
         }   

         DataColumn[] secondColumns = new DataColumn[ds.Tables[1].Columns.Count];   
         for (int i = 0; i < secondColumns.Length; i++)   
         {   
             secondColumns[i] = ds.Tables[1].Columns[i];   
         }   

         //Create DataRelation   
         DataRelation r1 = new DataRelation(string.Empty, firstColumns, secondColumns, false);   
         ds.Relations.Add(r1);   

         DataRelation r2 = new DataRelation(string.Empty, secondColumns, firstColumns, false);   
         ds.Relations.Add(r2);   

         //Create columns for return table   
         for (int i = 0; i < FirstDataTable.Columns.Count; i++)   
         {   
             ResultDataTable.Columns.Add(FirstDataTable.Columns[i].ColumnName, FirstDataTable.Columns[i].DataType);   
         }   

         //If FirstDataTable Row not in SecondDataTable, Add to ResultDataTable.   
         ResultDataTable.BeginLoadData();   
         foreach (DataRow parentrow in ds.Tables[0].Rows)   
         {   
             DataRow[] childrows = parentrow.GetChildRows(r1);   
             if (childrows == null || childrows.Length == 0)   
                 ResultDataTable.LoadDataRow(parentrow.ItemArray, true);   
         }   

         //If SecondDataTable Row not in FirstDataTable, Add to ResultDataTable.   
         foreach (DataRow parentrow in ds.Tables[1].Rows)   
         {   
             DataRow[] childrows = parentrow.GetChildRows(r2);   
             if (childrows == null || childrows.Length == 0)   
                 ResultDataTable.LoadDataRow(parentrow.ItemArray, true);   
         }   
         ResultDataTable.EndLoadData();   
     }   

     return ResultDataTable;   
 }  
#endregion