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    <p>I've found a pattern which I think works best--In my case, at least. <br /><br /><br /> I extend entity classes using partial classes. I use partial classes so the signature of the entity does not change (see the <code>DeleteOnSubmit</code> call in the <code>Delete</code> method).</p> <p>I've cooked up a a small example. Here's an image of the database and LINQ to SQL class setup:</p> <p><img src="https://i.stack.imgur.com/WqEHH.png" /> <br /><br /> And here's the partial class in which I implement business logic:</p> <pre><code>/// &lt;summary&gt; /// This class extends BusinessLogicDataContext.Products entity class /// &lt;/summary&gt; public partial class Product { /// &lt;summary&gt; /// New up a product by column: dbo.Products.ProductId in database /// &lt;/summary&gt; public Product(Int32 id) { var dc = new BusinessLogicDataContext(); // query database for the product var query = ( from p in dc.Products where p.ProductId == id select p ).FirstOrDefault(); // if database-entry does not exist in database, exit if (query == null) return; /* if product exists, populate self (this._ProductId and this._ProductName are both auto-generated private variables of the entity class which corresponds to the auto-generated public properties: ProductId and ProductName) */ this._ProductId = query.ProductId; this._ProductName = query.ProductName; } /// &lt;summary&gt; /// Delete product /// &lt;/summary&gt; public void Delete() { // if self is not poulated, exit if (this._ProductId == 0) return; var dc = new BusinessLogicDataContext(); // delete entry in database dc.Products.DeleteOnSubmit(this); dc.SubmitChanges(); // reset self (you could implement IDisposable here) this._ProductId = 0; this._ProductName = ""; } } </code></pre> <p>Using the implemented business logic:</p> <pre><code>// new up a product var p = new Product(1); // p.ProductId: 1, p.ProductName: "A car" // delete the product p.Delete(); // p.ProductId: 0, p.ProductName: "" </code></pre> <p>Furthermore: LINQ to SQL entity classes are very open in nature. This means that the property corresponding to the <em>dbo.Products.ProductId</em> column implements both a getter and a setter--this field should not be changeable.</p> <p>To my knowledge you can't override properties using partial classes, so what I usually do is implement a manager which narrows the object using an interface:</p> <pre><code>public interface IProduct { Int32 ProductId { get; } void Delete(); } </code></pre>
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