I think the problem is that you don't understand .NET DataSets. A DataTable retains the "original" copy of each value loaded into it. When a value is changed, the DataTable is able to detect the change. Likewise, the DataTable keeps track of rows that have been added or deleted. The HasChanges() function simply crawls through the DataTables and checks to see if there's been any changes (changed value, new rows, deleted rows, etc.)
See the MSDN documentation:
http://msdn.microsoft.com/en-us/library/system.data.dataset.haschanges.aspx
Comparing two DataSets is tricky, and I'm not aware of any built-in function to handle this (since every programmer will have their own definition of "equivalence").
See:
The code below will compare two DataTables by looking for added/deleted rows based on a Key column and modified rows by comparing the values of matching rows (again, based on the key). It would be fairly trivial to expand this to compare DataSets (by comparing similarly-named tables between DataSets).
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
namespace DataSetComparison
{
class Program
{
static void Main( string[] args )
{
var l_table1 = new DataTable();
l_table1.Columns.Add( "Key", typeof( int ) );
l_table1.Columns.Add( "Name", typeof( string ) );
l_table1.Columns.Add( "Age", typeof( int ) );
var l_table2 = new DataTable();
l_table2.Columns.Add( "Key", typeof( int ) );
l_table2.Columns.Add( "Name", typeof( string ) );
l_table2.Columns.Add( "Age", typeof( int ) );
l_table1.Rows.Add( l_table1.NewRow() );
l_table1.Rows[l_table1.Rows.Count - 1]["Key"] = 0;
l_table1.Rows[l_table1.Rows.Count - 1]["Name"] = "Alfred Harisson";
l_table1.Rows[l_table1.Rows.Count - 1]["Age"] = 36;
l_table1.Rows.Add( l_table1.NewRow() );
l_table1.Rows[l_table1.Rows.Count - 1]["Key"] = 1;
l_table1.Rows[l_table1.Rows.Count - 1]["Name"] = "Matthew George";
l_table1.Rows[l_table1.Rows.Count - 1]["Age"] = 41;
l_table1.Rows.Add( l_table1.NewRow() );
l_table1.Rows[l_table1.Rows.Count - 1]["Key"] = 2;
l_table1.Rows[l_table1.Rows.Count - 1]["Name"] = "Franklin Henry";
l_table1.Rows[l_table1.Rows.Count - 1]["Age"] = 33;
l_table2.Rows.Add( l_table2.NewRow() );
l_table2.Rows[l_table2.Rows.Count - 1]["Key"] = 0;
l_table2.Rows[l_table2.Rows.Count - 1]["Name"] = "Alfred Harisson";
l_table2.Rows[l_table2.Rows.Count - 1]["Age"] = 36;
l_table2.Rows.Add( l_table2.NewRow() );
l_table2.Rows[l_table2.Rows.Count - 1]["Key"] = 1;
l_table2.Rows[l_table2.Rows.Count - 1]["Name"] = "Matthew George";
l_table2.Rows[l_table2.Rows.Count - 1]["Age"] = 42; // Record 1 "modified"
// Record 2 "deleted"
// Record 3 "added":
l_table2.Rows.Add( l_table2.NewRow() );
l_table2.Rows[l_table2.Rows.Count - 1]["Key"] = 3;
l_table2.Rows[l_table2.Rows.Count - 1]["Name"] = "Lester Kulick";
l_table2.Rows[l_table2.Rows.Count - 1]["Age"] = 33;
// Using table 1 as the control, find changes in table 2
// Find deleted rows:
var l_table2Keys = l_table2.Select().Select( ( r ) => (int) r["Key"] );
var l_deletedRows = l_table1.Select().Where( ( r ) => !l_table2Keys.Contains( (int) r["Key"] ) );
foreach ( var l_deletedRow in l_deletedRows )
Console.WriteLine( "Record " + l_deletedRow["Key"].ToString() + " was deleted from table 2." );
// Find added rows:
var l_table1Keys = l_table1.Select().Select( ( r ) => (int) r["Key"] );
var l_addedRows = l_table2.Select().Where( ( r ) => !l_table1Keys.Contains( (int) r["Key"] ) );
foreach ( var l_addedRow in l_addedRows )
Console.WriteLine( "Record " + l_addedRow["Key"].ToString() + " was added to table 2." );
// Find modified rows:
var l_modifiedRows = l_table2.Select()
.Join(
l_table1.Select(),
r => (int) r["Key"],
r => (int) r["Key"],
( r1, r2 ) => new
{
Row1 = r1,
Row2 = r2
} )
.Where(
values => !( values.Row1["Name"].Equals( values.Row2["Name"] ) &&
values.Row1["Age"].Equals( values.Row2["Age"] ) ) )
.Select( values => values.Row2 );
foreach ( var l_modifiedRow in l_modifiedRows )
Console.WriteLine( "Record " + l_modifiedRow["Key"].ToString() + " was modified in table 2." );
Console.WriteLine( "Press any key to quit..." );
Console.ReadKey( true );
}
}
}
Console output:
Record 2 was deleted from table 2.
Record 3 was added to table 2.
Record 1 was modified in table 2.
