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POWhy do I need to perform a deep clone to get this code to work?
 

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  1. POWhy do I need to perform a deep clone to get this code to work?
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    <p>The following code works. However, it works because I end up creating a deep clone of the suppliers. If I do not perform a deep clone then we get an error suggesting that the supplier objects have changed and the attempt to amend the supplier table has failed. This only happens if the following line is run: <code>foreach (Supplier suppliers in exceptions)</code>. Oddly, this occurs irrespective whether the <code>Delete()</code> method is executed. Why does this happen? I have posted the working code below for your inspection. As I say, if you try looping without deep cloning then it does not work... Any ideas? </p> <pre><code>public void DeleteSuppliers(IList&lt;Supplier&gt; suppliers, Int32 parentID) { // If a supplier has been deleted on the form we need to delete from the database. // Get the suppliers from the database List&lt;Supplier&gt; dbSuppliers = Supplier.FindAllByParentID(parentID); // So return any suppliers that are in the database that are not now on this form IEnumerable&lt;Supplier&gt; results = dbSuppliers.Where(f =&gt; !Suppliers.Any(d =&gt; d.Id == f.Id)); IList&lt;Supplier&gt; exceptions = null; // code guard if (results != null) { // cast as a list IList&lt;Supplier&gt; tempList = (IList&lt;Supplier&gt;)results.ToList(); // deep clone otherwise there would be an error exceptions = (IList&lt;Supplier&gt;)ObjectHelper.DeepClone(tempList); // explicit clean up tempList = null; } // Delete the exceptions from the database if (exceptions != null) { // walk the suppliers that were deleted from the form foreach (Supplier suppliers in exceptions) { // delete the supplier from the database suppliers.Delete(); } } } </code></pre>
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    1. PO
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    1. USCarneyCode
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    1. COWhat is the exact error?
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      1. POWhy do I need to perform a deep clone to get this code to work?
      1. USMarc Gravell
    2. COBTW, I would like to point out an unrelated pointless piece of code here that I see frequently in code reviews involving LINQ for some reason. Your test for "results != null" is pointless. That will never be false. It will always refer to an IEnumerable instance. There may be 0 objects in the collection, but the collection instance will always exist.
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      1. POWhy do I need to perform a deep clone to get this code to work?
      1. USBlueMonkMN
    3. COso I should just use results.Count > 0 or something instead?
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      1. POWhy do I need to perform a deep clone to get this code to work?
      1. USCarneyCode
 

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