by Miha Markič
8. November 2008 16:09
Here is an example where an extension method is useful. Take this [LGP] 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 [LGP] 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:
public static class Tubular
{
public static 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:
public static class Tubular
{
public static 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?