I wanted to share my implementation using Jon's answer above as a starting point. In this case, rather than sorting by a string property name coming from the presentation layer (since the title of this question isn't specific about that), I am building out an Entity Framework data layer and want to allow its consumer to specify order by properties as lambda expressions. I.E. Rather than passing "sidx", I wanted to be able to use p => p.sidx. I also wanted to be able to pass an unlimited number of order by properties and be able to specify ascending or descending order.
Well my method can accept such a lambda expression as type Expression<Func<T, object>>. That let's me call it the way I want but the problem is, Entity Framework can't translate the expression to SQL unless the second generic parameter is strongly typed. The OrderBy extension method requires two generic parameters: T - the type the property belongs to, and TKey - the type the property returns. So the first step was to modify Jon's example to convert a given Expression<Func<T, object>> to a Expression<Func<T, Tkey>> (once we're working within the context of a query, we can determine the type TKey):
internal static IQueryable<T> OrderByDynamic<T>(this IQueryable<T> source, Expression<Func<T, object>> sortExp)
{
//We need to convert the key selector from Expression<Func<T, object>> to a strongly typed Expression<Func<T, TKey>>
//in order for Entity Framework to be able to translate it to SQL
MemberExpression orderByMemExp = ExpressionHelpers.RemoveConvert(sortExp.Body) as MemberExpression;
ParameterExpression sourceParam = sortExp.Parameters[0];
LambdaExpression orderByLamda = Expression.Lambda(orderByMemExp, new[] { sourceParam });
MethodInfo orderByMethod = OrderByMethod.MakeGenericMethod(new[] { typeof(T), orderByMemExp.Type });
//Call OrderBy or OrderByDescending on the source IQueryable<T>
return (IQueryable<T>)orderByMethod.Invoke(null, new object[] { source, orderByLamda });
}
As I mentioned, I want to accept an unlimited number of order by key selectors and also have the ability to specify the ascending or descending direction so I made a wrapper class for the Expression<Func<T, object>> which I named DynamicSortExpression:
public class DynamicSortExpression<T>
{
/// <summary>
/// Creates a new ascending DynamicSortExpression
/// </summary>
/// <param name="keySelector">A MemberExpression identifying the property to sort on</param>
public DynamicSortExpression(Expression<Func<T, object>> keySelector) : this(keySelector, false)
{
}
public DynamicSortExpression(Expression<Func<T, object>> keySelector, bool descending)
{
this.KeySelector = keySelector;
this.Desc = descending;
}
/// <summary>
/// Gets the expression that selects the property of T to sort on
/// </summary>
public Expression<Func<T, object>> KeySelector { get; }
/// <summary>
/// Gets sort expression is in ascending or descending order
/// </summary>
public bool Desc { get; }
}
Then I updated the extension method to accept this type and created an overload for OrderBy that receives a List<DynamicSortExpression<T>> and adds them to the query using the extension method(s) one by one. Here is the final result:
public static class Extensions
{
private static readonly MethodInfo OrderByMethod = typeof(Queryable).GetMethods()
.Where(method => method.Name == "OrderBy")
.Where(method => method.GetParameters().Length == 2)
.Single();
private static readonly MethodInfo OrderByDescMethod = typeof(Queryable).GetMethods()
.Where(method => method.Name == "OrderByDescending")
.Where(method => method.GetParameters().Length == 2)
.Single();
private static readonly MethodInfo ThenByMethod = typeof(Queryable).GetMethods()
.Where(method => method.Name == "ThenBy")
.Where(method => method.GetParameters().Length == 2)
.Single();
private static readonly MethodInfo ThenByDescMethod = typeof(Queryable).GetMethods()
.Where(method => method.Name == "ThenByDescending")
.Where(method => method.GetParameters().Length == 2)
.Single();
internal static IQueryable<T> OrderBy<T>(this IQueryable<T> sourceQuery, List<DynamicSortExpression<T>> orderBy)
{
bool isFirst = true;
foreach (var sortExpression in orderBy)
{
if (isFirst)
{
sourceQuery = sourceQuery.OrderByDynamic(sortExpression);
isFirst = false;
}
else
sourceQuery = sourceQuery.ThenByDynamic(sortExpression);
}
return sourceQuery;
}
internal static IQueryable<T> OrderByDynamic<T>(this IQueryable<T> source, DynamicSortExpression<T> sortExpression)
{
//We need to convert the key selector from Expression<Func<T, object>> to a strongly typed Expression<Func<T, TKey>>
//in order for Entity Framework to be able to translate it to SQL
MemberExpression orderByMemExp = ExpressionHelpers.RemoveConvert(sortExpression.KeySelector.Body) as MemberExpression;
ParameterExpression sourceParam = sortExpression.KeySelector.Parameters[0];
LambdaExpression orderByLamda = Expression.Lambda(orderByMemExp, new[] { sourceParam });
MethodInfo orderByMethod = sortExpression.Desc ?
OrderByDescMethod.MakeGenericMethod(new[] { typeof(T), orderByMemExp.Type }) :
OrderByMethod.MakeGenericMethod(new[] { typeof(T), orderByMemExp.Type });
//Call OrderBy or OrderByDescending on the source IQueryable<T>
return (IQueryable<T>)orderByMethod.Invoke(null, new object[] { source, orderByLamda });
}
internal static IQueryable<T> ThenByDynamic<T>(this IQueryable<T> source, DynamicSortExpression<T> sortExpression)
{
//We need to convert the key selector from Expression<Func<T, object>> to a strongly typed Expression<Func<T, TKey>>
//in order for Entity Framework to be able to translate it to SQL
Expression orderByMemExp = ExpressionHelpers.RemoveConvert(sortExpression.KeySelector.Body) as MemberExpression;
ParameterExpression sourceParam = sortExpression.KeySelector.Parameters[0];
LambdaExpression orderByLamda = Expression.Lambda(orderByMemExp, new[] { sourceParam });
MethodInfo orderByMethod = sortExpression.Desc ?
ThenByDescMethod.MakeGenericMethod(new[] { typeof(T), orderByMemExp.Type }) :
ThenByMethod.MakeGenericMethod(new[] { typeof(T), orderByMemExp.Type });
//Call OrderBy or OrderByDescending on the source IQueryable<T>
return (IQueryable<T>)orderByMethod.Invoke(null, new object[] { source, orderByLamda });
}
}
Now my data layer can have a method like List<T> GetList(Expression<Func<T, bool>> where, params DynamicSortExpression<T>[] orderBy) that can be called like
new MyClass<Person>().GetList(p => p.FirstName == "Billy", //where clause
new DynamicSortExpression<Person>(p => p.FirstName),
new DynamicSortExpression<Person>(p => p.LastName, true));
Where internally, MyClass<T>.GetList builds the query which calls my OrderBy extension method. Something like:
DBContext.Set<T>().Where(whereParam).OrderBy(orderByParams);
The RemoveConvert method is something I yanked out of the EntityFramework source code to recursively remove Convert calls from a MemberExpression:
internal static Expression RemoveConvert(Expression expression)
{
System.Diagnostics.Debug.Assert(expression != null);
while ((expression != null)
&& (expression.NodeType == ExpressionType.Convert
|| expression.NodeType == ExpressionType.ConvertChecked))
{
expression = RemoveConvert(((UnaryExpression)expression).Operand);
}
return expression;
}
I hope this is helpful! Thanks Jon!
