Here is an example where an extension method is useful. Take this LLBLGen Pro code for example:
public EntityCollection<CustomersEntity> GetCustomers() {using (DataAccessAdapter da =new DataAccessAdapter("Data Source=[SERVER];Initial Catalog=Northwind;Integrated Security=True")) { LinqMetaData context =new LinqMetaData(da); var q = from c in context.Customers select c; EntityCollection<CustomersEntity> result = ((ILLBLGenProQuery)q).Execute<EntityCollection<CustomersEntity>>();return result; } }
It is a simple LINQ to LLBLGenPro select against (we all love) Northwind database. Pay attention at result assignment. To have data returned as a native LLBLGen Pro EntityCollection you have to resort to ILLBLGenProQuery interface. You have to use ILLBLGenProQuery.Execute method on IQueryable<T> q. A cast is obviously required because IQueryable<T> doesn't know anything about ILLBLGenProQuery. While this code works it is not exactly elegant - I am referring to the later cast of course.
So, the idea is to have something like this instead:
EntityCollection<CustomersEntity> result = q.Execute<EntityCollection<CustomersEntity>>();
Possible? Sure, just add this static class with a single extension method and you are good to go:
publicstaticclass Tubular {publicstatic TResult Execute<TResult>(this IQueryable q)where TResult : IEntityCollection2 {return ((ILLBLGenProQuery)q).Execute<TResult>(); } }
Or perhaps, we can further reduce the cluttering by introducing this extension method:
publicstaticclass Tubular {publicstatic EntityCollection<TEntity> Execute<TEntity>(this IQueryable q)where TEntity : EntityBase2, IEntity2 {return ((ILLBLGenProQuery)q).Execute<EntityCollection<TEntity>>(); } }
to achieve this, even less cluttered, line:
EntityCollection<CustomersEntity> result = q.Execute<CustomersEntity>();
Isn't this or former de-cluttered line more readable and more elegant than the original?