LINQ to SQL with Repository Pattern

Question

Hi all,

Currently I'm trying to implement LINQ to SQL in my project. I'm trying to use LINQ to SQL with the famous repository pattern. here is what I was trying to do:

1. Create table, for example customer table.
2. Generate LINQ to SQL (.dbml) for my customer table.
3. It generated partial Customer class complete with all the properties and some partial method.

After that I need to put some custom method for ex: GetCustomerById(int id), GetCustomerByName(string name), etc. So I create a partial class of Customer and implement all the function that I need.

Hmmm, from this step I realized that there is something weird that I haven't implemented the repository pattern.. T_T

What I was trying to do was create a business layer that access repository layer, and then repository layer use LINQ to SQL as data model and data access to SQL Server. Is this the best practice? and how to add repository pattern to my customer partial class generated by LINQ to SQL?

Thanks.

Answer 1

There are many variations of the Repository pattern. A simple definition of it is a module that encapsulates/hides the persistence logic from other components.

So you could have a class called LinqToSqlRepository.cs, with a method like so:

public class LinqToSqlRepository
{
   private YourDataContext _ctx;

   public LinqToSqlRepository()
   {
      _ctx = new YourDataContext();
   }

   public Person GetPersonById(int id)
   {
      return _ctx.Persons.SingleOrDefault(p => p.Id == id);
   }
}

And call it from your Business Layer like so:

var db = new LinqToSqlRepository();
var person = db.GetPersonById(int id);

Ideally you don't want to add your repository to your partial class. It should be seperate. Your Repository class should work off your partial classes.

To be honest though, (IMO) this kind of design pattern is better suited for EntityFramework than Linq2Sql, as it offers much more versatility in terms of POCO's.

There is no way with Linq2Sql to completely de-couple the business entities from the persistence layer. In the above example, you are returning a Person object, which is actually the entity in the L2S designer, therefore the UI will need a reference to this, defeating the point of 'persistence-ignorance'.

However as i said, create your Repository seperate, don't put the methods in the partial class, work with them in your Repository.

HTH.

Answer 2

Anyway, use LINQ to Entities.

LINQ to SQL is obsolete