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using System.Linq;
using System.Linq.Expressions;
namespace System.Web.UI.WebControls {
public static class QueryExtensions {
private const string SORT_DIRECTION_DESC = " DESC";
public static IQueryable<T> SortBy<T>(this IQueryable<T> source, string sortExpression) where T : class {
if (source == null) {
throw new ArgumentNullException("source");
}
if (String.IsNullOrWhiteSpace(sortExpression)) {
return source;
}
sortExpression = sortExpression.Trim();
bool isDescending = false;
// DataSource control passes the sort parameter with a direction
// if the direction is descending
if (sortExpression.EndsWith(SORT_DIRECTION_DESC, StringComparison.OrdinalIgnoreCase)) {
isDescending = true;
int descIndex = sortExpression.Length - SORT_DIRECTION_DESC.Length;
sortExpression = sortExpression.Substring(0, descIndex).Trim();
}
if (String.IsNullOrEmpty(sortExpression)) {
return source;
}
ParameterExpression parameter = Expression.Parameter(source.ElementType, String.Empty);
MemberExpression property = Expression.Property(parameter, sortExpression);
LambdaExpression lambda = Expression.Lambda(property, parameter);
string methodName = (isDescending) ? "OrderByDescending" : "OrderBy" ;
Expression methodCallExpression = Expression.Call(typeof(Queryable), methodName,
new Type[] { source.ElementType, property.Type },
source.Expression, Expression.Quote(lambda));
return (IQueryable<T>)source.Provider.CreateQuery(methodCallExpression);
}
}
}
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