Tag: Extension

Linq OrderBy Extension using a string

When writing more complicated Linq queries against an ORM, it is often desirable to be able to randomly pass in a field name as a string and sort order (direction) on the fly. This comes in especially handy for the paging project that you’ll also find on this Blog. I developed this Linq OrderBy Extension using a string and boolean value to determine if should sort ascending or descending.

Basically, with out of the box Linq, you can’t easily change the sort column dynamically. There is a Dynamic Linq Library (System.Linq.Dynamic) that you can install using a NuGet package, but that seemed overkill to me for this need. After looking that over, if you feel it’s a better solution for you, you won’t need to use this extension.

This extension method allows you to pass in the collection as IQueryable, so you can pass in Linq queries that haven’t been executed yet. Then it accepts your OrderByProperty and whether you want the query set to sort the results Descending as a boolean value.

You implement it like this:

using (EFModels.AWEntities _efEntities = new EFModels.AWEntities())
{
    var _entityrows = (from sheader in _efEntities.SalesOrderHeaders
                       select sheader);

    if (!string.IsNullOrWhiteSpace(SortExpression))
    {
        bool IsSortDESC = false;
        if (SortOrder.ToLower() == "asc") { IsSortDESC = true; }
  
        _entityrows = _entityrows.OrderBy(SortExpression, IsSortDESC);
    }

	return _entityrows.ToList();
	
}

Put the following Extension in your extensions class and make sure to put a using to that location at the top of the class where you’re going to use it.

    /// <summary>
    /// Implementation of OrderBy Extension Method for IQueryable Collections
    /// </summary>
    /// <typeparam name="TEntity">Generic Type Object</typeparam>
    /// <param name="p_Source">The collection to order</param>
    /// <param name="p_OrderByProperty">The property to order by</param>
    /// <param name="p_Descending">True to sort Descending</param>
    /// <returns></returns>
    public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> p_Source, string p_OrderByProperty, bool p_Descending)
    {
        try
        {
            string command = p_Descending ? "OrderByDescending" : "OrderBy";
            var type = typeof(TEntity);
            var property = type.GetProperty(p_OrderByProperty);
            var parameter = Expression.Parameter(type, "p");
            var propertyAccess = Expression.MakeMemberAccess(parameter, property);
            var orderByExpression = Expression.Lambda(propertyAccess, parameter);
            var resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType },
                                          p_Source.Expression, Expression.Quote(orderByExpression));
            return p_Source.Provider.CreateQuery<TEntity>(resultExpression);
        }
        catch (ArgumentNullException)
        {
            throw new Exception("The OrderByProperty value of: '" + p_OrderByProperty + "', was empty or is not a proper column name!");
        }
        catch (Exception)
        {
            throw;
        }
    }

If you like this, take a look at some other extension methods that I use all the time:

Jack’s Top 10 String Extension Methods
Trim String to Particular Length