linq2SQL + OrderBy string value

Question

Hi Guys

I wonder if this is possible

var table = _db.GetTable<T>();
var data = table.Where(t => !t.Deleted).OrderBy("Name");

I cannot do t.Name as t only have Id and Deleted

The base class which contains this method looks like this

public class RepositoryBase<T> where T : class, Interfaces.IModel

IModel only knows of Deleted and Id

Regards

Answer 1

It the underlying type doesn't have an obvious Name member, this I can't see how this would work.

If the problem is simpy that you only know the column to order by at runtime; then to order by a dynamic property you need to build an Expression on the fly. Here's some old code I have that does this, and should support "Name" and things like "Customer.Name" (child properties); I haven't tested it recently, though:

public static class OrderExtensions {
   public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
   {
       return ApplyOrder<T>(source, property, "OrderBy");
   }
   public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
   {
       return ApplyOrder<T>(source, property, "OrderByDescending");
   }
   public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
   {
       return ApplyOrder<T>(source, property, "ThenBy");
   }
   public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T>  source, string property)
   {
       return ApplyOrder<T>(source, property, "ThenByDescending");
   }
   static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName) {
       ParameterExpression arg = Expression.Parameter(typeof(T), "x");
       Expression expr = arg;
       foreach(string prop in property.Split('.')) {
           // use reflection (not ComponentModel) to mirror LINQ
           expr = Expression.PropertyOrField(expr, prop);
       }
       Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), expr.Type);
       LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);

       return (IOrderedQueryable<T>) typeof(Queryable).GetMethods().Single(
               method => method.Name == methodName
                       && method.IsGenericMethodDefinition
                       && method.GetGenericArguments( ).Length ==2
                       && method.GetParameters().Length == 2)
               .MakeGenericMethod(typeof(T), expr.Type)
               .Invoke(null, new object[] {source, lambda});
  }
}

Answer 2

I think you need to create a specific repository for this entity since your abstraction model doesn't fit for this case. Something like:

public class MyEntityRepository : RepositoryBase<MyEntity>