Using OnValidate method in LINQ to SQL

If you are using LINQ to SQL you may have noticed the OnValidate partial method.

public partial class Person : INotifyPropertyChanging,
                  INotifyPropertyChanged
{
     ...
     partial void OnValidate(ChangeAction action);
     ...
}

This method gets automatically called when the class participates in the DataContext SubmitChanges.

When working with LINQ to SQL classes I prefer to keep my code generated classes separated from any modifications or customisations.  Normally, I will create a folder in my project called ExtendedClasses, there I can extend my business objects, giving them a <classname>.extended.cs file name.  This allows me to regenerate my business objects without fear of losing these customisations.

So, in my extended class file I will include...

partial void OnValidate(ChangeAction action)
{
    if (action == ChangeAction.Insert)
    {
        //Do validation for inserts
    }
   
    if (action==ChangeAction.Insert ||
        action==ChangeAction.Update)
    {
        //Do basic validation for inserts and updates
    }
}

I avoid including any business rules in this class level validation, and stick to data related validation, such as field lengths, data ranges and required fields all based on my data model.  Any validation errors get raised by throwing an exception.
Because the OnValidate method is private, you may want to include a public Validate method.

public void Validate()
{
    if (PersonId==Guid.Empty)
    {
        OnValidate(ChangeAction.Insert);
    }
    else
    {
        OnValidate(ChangeAction.Update);
    }
}

With the public Validate method I can validate my business object from the UI layer before passing it down to my services layer.

try
{
    person.Validate();
}
catch (Exception e)
{
    MessageBox.Show(e.Message + "\n\n" + e.StackTrace);
    return;
}

UK Post Code Search using LINQ to XML

I recently delved into working with UK Post Codes, including validation and searching.  This is not my first contact with this area, and in the past it has always involved large SQL tables or by using third-party products.

This time, I was looking for something a bit more portable, like XML.

I was able to find freeware downloads of UK Post Codes including their longitude and latitude, which was easily imported into a SQL Server database.

I've created a class library called PostCodes.UK, which contains useful methods for validating post codes and determining which post codes fall within a given radial distance from a target post code.  All of the search and validation routines utilise LINQ to XML to query the XDocument.

The class library relies on a PostCodes.xml file (supplied in the Test Harness project), which gets loaded as an XDocument.  I've included a small WPF Test Harness application which illustrates how this library is used.

To run this solution you will need Visual Studio 2008 SP1.  The source code is available here.

For those interested in this area, there is an informative government page on Postal Geography, which explains the structure of the UK post codes.  You should be aware that UK post codes are always changing; however, if all you need is outward code resolution (e.g. PO6 ), chances are you can make do with public domain data.

Another site with useful information is: http://www.easypeasy.com/guides/article.php?article=64