How to check for the presence of an OrderBy in a ObjectQuery expression tree

Question

I\'m using T4 for generating repositories for LINQ to Entities entities.

The repository contains (amongst other things) a List method suitable for paging. The docum

Answer 1

Paging depends on Ordering in a strong way. Why not tightly couple the operations? Here's one way to do that:

Support objects

public interface IOrderByExpression
{
  ApplyOrdering(ref IQueryable query);
}

public class OrderByExpression : IOrderByExpression
{
  public IQueryable ApplyOrderBy(ref IQueryable query)
  {
    query = query.OrderBy(exp);
  }
  //TODO OrderByDescending, ThenBy, ThenByDescending methods.

  private Expression> exp = null;

  //TODO bool descending?
  public OrderByExpression (Expression> myExpression)
  {
    exp = myExpression;
  }
}

The method under discussion:

public IQueryable List(int startIndex, int count, IOrderByExpression ordering)
{
    NorthwindEntities ent = new NorthwindEntities();
    IQueryable query = ent.Categories;
    if (ordering == null)
    {
      ordering = new OrderByExpression(c => c.CategoryID)
    }
    ordering.ApplyOrdering(ref query);

    return query.Skip(startIndex).Take(count);
}

Some time later, calling the method:

var query = List(20, 20, new OrderByExpression(c => c.CategoryName));