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POWhy Won't Two Indentical DataTables Show Any Differences?
 

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  1. POWhy Won't Two Indentical DataTables Show Any Differences?
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    <p>I am using <code>DataRelation</code> to compare two <code>DataTable</code> and return a third table containing the rows that are not share by both original tables by using this <a href="http://weblogs.sqlteam.com/davidm/archive/2004/01/19/739.aspx" rel="nofollow noreferrer">tutorial</a>. Below is the code.</p> <pre><code>public static DataTable Difference(DataTable First, DataTable Second) { //Create Empty Table DataTable table = new DataTable("Difference"); //Must use a Dataset to make use of a DataRelation object using(DataSet ds = new DataSet()) { //Add tables ds.Tables.AddRange(new DataTable[]{First.Copy(),Second.Copy()}); //Get Columns for DataRelation DataColumn[] firstcolumns = new DataColumn[ds.Tables[0].Columns.Count]; for(int i = 0; i &lt; firstcolumns.Length; i++) { firstcolumns[i] = ds.Tables[0].Columns[i]; } DataColumn[] secondcolumns = new DataColumn[ds.Tables[1].Columns.Count]; for(int i = 0; i &lt; secondcolumns.Length; i++) { secondcolumns[i] = ds.Tables[1].Columns[i]; } //Create DataRelation DataRelation r = new DataRelation(string.Empty,firstcolumns,secondcolumns,false); ds.Relations.Add(r); //Create columns for return table for(int i = 0; i &lt; First.Columns.Count; i++) { table.Columns.Add(First.Columns[i].ColumnName, First.Columns[i].DataType); } //If First Row not in Second, Add to return table. table.BeginLoadData(); foreach(DataRow parentrow in ds.Tables[0].Rows) { DataRow[] childrows = parentrow.GetChildRows(r); if(childrows == null || childrows.Length == 0) table.LoadDataRow(parentrow.ItemArray,true); } table.EndLoadData(); } return table; } </code></pre> <p>Surprisingly enough when I exercised this code, it only worked on few cases and failed in others.</p> <p>There was one case, I was comparing two identical table (but has different source) that both has:</p> <ul> <li>Same Column Name &amp; <code>DataType</code></li> <li>Same Number of Rows &amp; Columns</li> <li>Same Value in Each Cells</li> </ul> <p>Only to have a brand <strong>new table returned that actually has the exact same composition</strong> as the two original tables!</p> <p>What did I <strong>possibly miss</strong>?</p> <p>Is it possible that two <strong>identical tables</strong> (sharing features I mentioned above) can have <strong>other different properties</strong> (which doesn't seem visible to users' eyes)?</p> <p>Or is it possible that this is actually a <strong>bad method</strong>? What are the possible alternatives?</p> <p>Any advise is highly appreciated.</p> <p>Regards</p> <p><strong>EDITED</strong></p> <ol> <li>Both tables have same primitive datatype such as: <code>System.String</code>, <code>System.Int32</code>, <code>System.DateTime</code></li> <li>These code doesn't work on all samples I tested</li> <li>Here is a print screen of 1 sample (using <code>DataSet</code> Visualizer)</li> </ol> <p><img src="https://i.stack.imgur.com/cpjjg.png" alt="enter image description here"></p>
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    1. This table or related slice is empty.
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    1. USrofans91
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    1. This table or related slice is empty.
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      1. POWhy Won't Two Indentical DataTables Show Any Differences?
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    1. COWhat are the datatypes of these columns? Is it just primitives? Perhaps they contain some objects which are not equal by reference? `(...) but has different source (...)` could be the key here. You should be aware that after something like (for example) `var bitmapA = Bitmap.FromFile(@"C:\picture.jpg"); var bitmapB = Bitmap.FromFile(@"C:\picture.jpg");` - `bitmapA == bitmapB` is `false`
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      1. USKonrad Morawski
    2. COIn theory the method should work. In the case where an expected match didn't work, were the columns in the same order? Can you provide a small example that doesn't work?
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    3. COTomorrow I shall, after I got back at the office =)
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