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copied!<p>The reason this fails is two fold.</p> <ol> <li>In order to update a Reference (i.e. Product.Category) you have to have the original reference value in the context too.</li> <li>ApplyPropertyChanges(...) only applies to regular / scalar properties of the Entity, the reference is left unchanged</li> </ol> <p>So I would do something like this (Note this code makes heavy use of a trick called <a href="http://blogs.msdn.com/alexj/archive/2009/06/19/tip-26-how-to-avoid-database-queries-using-stub-entities.aspx" rel="nofollow noreferrer">stub entities</a> to avoid mucking around with EntityKeys)</p> <pre><code>Product product = new Product(); // Use a stub because it is much easier. product.Category = new Category {CategoryID = selectedCategoryID}; product.Name = txtName.Text.Trim(); ... other properties StockControlDAL.EditProduct(productId, originalCategoryID); public static void EditProduct(Product product, int originalCategoryID ) { using(var context = new ShopEntities()) { // Attach a stub entity (and stub related entity) var databaseProduct = new Product { ProductID = product.ProductID, Category = new Category {CategoryID = originalCategoryID} }; context.AttachTo("Products", databaseProduct); // Okay everything is now in the original state // NOTE: No need to call AcceptAllChanges() etc, because // Attach puts things into ObjectContext in the unchanged state // Copy the scalar properties across from updated product // into databaseProduct in the ObjectContext context.ApplyPropertyChanges("ShopEntities.Products", product); // Need to attach the updated Category and modify the // databaseProduct.Category but only if the Category has changed. // Again using a stub. if (databaseProduct.Category.CategoryID != product.Category.CategoryID) { var newlySelectedCategory = new Category { CategoryID = product.Category.CategoryID }; context.AttachTo("Categories", newlySelectedCategory) databaseProduct.Category = newlySelectedCategory; } context.SaveChanges(); } } </code></pre> <p>This will do the job, assuming no typos etc.</p>

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