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    <p>The Linq2SQL classes are <em>partial classes</em>, which means you can easily extend them by adding your own separate file and declaring another part of the partial class in there.</p> <p>In that file, you can customize the class as needed - and since it's a separate file, the code generation will not overwrite it.</p> <p>If you look at e.g. the "Contact" class in the AdventureWorks database, Linq2SQL will generate this in your AdventureWorks.designer.cs file:</p> <pre><code>[Table(Name="Person.Contact")] public partial class Contact : INotifyPropertyChanging, INotifyPropertyChanged { </code></pre> <p>Now you can add a "Contact.cs" file to your project, and extend that partial class, e.g. by introducing a new property "DisplayName":</p> <pre><code>public partial class Contact { public string DisplayName { get { return string.Format("{0} {1}", FirstName, LastName); } } } </code></pre> <p>At compile time, these two parts of the class are merged together.</p> <p>The other part are the partial methods - methods that are available for you to implement, but if they're not implemented, calls to them are being optimized out by the compiler.</p> <p>For each object class in Linq2SQL, a whole slew of partial methods (a new feature in .NET 3.0) are being created - up to you to implement those!</p> <pre><code>partial void InsertContact(Contact instance); partial void UpdateContact(Contact instance); partial void DeleteContact(Contact instance); partial void OnLoaded(); partial void OnValidate(System.Data.Linq.ChangeAction action); partial void OnCreated(); partial void OnFirstNameChanging(string value); partial void OnFirstNameChanged(); partial void OnLastNameChanging(string value); partial void OnLastNameChanged(); </code></pre> <p>Plenty of extension points!</p> <p>Marc</p>
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    1. POHow to customise properties on a Linq2SQL entity?
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    1. COYeah, sorry, I understand the concept of partial classes and how they work. My question is how you customise properties. You cannot define a property in a partial file with the same name as an autogenerated property - so the question remains, how do you customise properties in Linq2SQL entities? In your example, if DisplayName is a column in the db, you have no way that I can see of customising the encapsulated behaviour inside that property...
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    2. CO@Malcolm: no, existing properties can't be "overridden" or tweaked. In this case, you probably should look at using a template-based approach to create your Linq objects, and tweak the template to make the properties virtual so you can override them in a derived class.
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    3. COahh ok, thanks, do you have any decent links to working with L2S in a more advanced way? templates for example?
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