In this post, I am going to show how you to extend a class generated by ORM tools. To demonstrate this, I am using a LINQ to SQL ORM.

When you make use of an ORM tool like LINQ to SQL or Entity-Framework, it generates the classes from the database structure given as input. For example, consider the below example:

Now I want to display the list of products in my grid but I have to display the product name with categoryname, for example, productname(categoryname), or consider a situation where I have an ordertable and I have to display one more extra column in the grid with display total = quantity * price.

To achieve this, look at the class generated by the ORM tools. In the class definition, you will see it is decorated with the partial keyword. A C# 2.0 partial class allows us to create a class which expands in two different files and at compile time, both files get compiled in one class. So by making use of the same rule, I have added one more class file and it is partial, as below:

public partial class Product
{
   public string ProductWithCategory
   {
      get
      {
         return this.ProductName + "(" + this.Category +")";
      }
   }
}

Now, we can consume the property in the presentation or business layer, like below:

var productlist = (from p in context.Products select p).ToList();
foreach (Product p in productlist)
{
   Console.WriteLine(p.ProductWithCategory);
}

So in the above way, by adding a property to a partial class, we can easily achieve the task.

Summary

By using a partial class, we can add custom logic to a class created by the ORM tool(s).