Dynamic Lambda Expression call

Question

I'm getting this exception when I run this code.

ParameterExpression of type System.Int64 cannot be used for delegate parameter of type System.Object

I know it's something to do with the Expression.Lambda<func<object,bool>> part of the code. Overall, I want to pass any type of ParameterExpression into this method and it will call the expression.

public static IQueryable<T> OrderData<T>(IQueryable<T> data)
{
    try
    {
        Order order = Order.ASC;
        var result = Enum.TryParse<Order>(_gridSettings.SortOrder, true, out order);
        if (_gridSettings.IsSearch)
        {
            data = ExpressionSort(order, data, typeof(T).GetProperty(_gridSettings.SortColumn));
        }
        else
        {
            data = ExpressionSort(order, data, _defaultColumn);
        }
    }
    catch (Exception ex)
    {
        log.WriteLog(MethodBase.GetCurrentMethod(), LogLevel.FATAL, ex);
    }
    return data;
}

private static IQueryable<T> ExpressionSort<T>(Order order, IQueryable<T> data, PropertyInfo property)
{
    // Compose the expression tree that represents the parameter to the predicate.
    ParameterExpression paramExpression = Expression.Parameter(property.PropertyType, property.Name);
    IQueryable<T> queryableData = data.AsQueryable<T>();
    switch (order)
    {
        case Order.ASC:
            return ExecuteCall(paramExpression, paramExpression, queryableData, "OrderBy");
        case Order.DESC:
            return ExecuteCall(paramExpression, paramExpression, queryableData, "OrderByDescending");
    }
    return data;
}

private static IQueryable<T> ExecuteCall<T>(Expression expression, ParameterExpression paramExpression, IQueryable<T> queryableData, string linqMethod)
{
    MethodCallExpression callExpression = Expression.Call(
                               typeof(Queryable),
                               linqMethod,
                               new Type[] { queryableData.ElementType },
                               queryableData.Expression,
                               Expression.Lambda<Func<object, bool>>(expression, new ParameterExpression[] { paramExpression }));
    // Create an executable query from the expression tree.
    return queryableData.Provider.CreateQuery<T>(callExpression);
}

EDIT: I did see this answer to a similar question

Expression of type 'System.Int32' cannot be used for return type 'System.Object' I do not know how to apply it to my code though

EDIT 2: The main issue is that thisExpression.Lambda<Func<object, bool>>(conversion, new ParameterExpression[] { paramExpression })); line is giving me an exception. paramExpression contains an Int64 but its expectinng an object. I dont know how to dynamically tell the Func from the information I already have or if that is possible.

GOAL: I am trying to do something like this data.OrderBy(x=>x.DynamicProperty);

You are using T<object, bool> and your parameter is a struct... you can't cast an struct to object — Fabio
– Fabio, Commented May 16, 2015 at 3:29
Can you post an example of how you are using this, as it stands right now? Without that it's difficult to assess how to fix it. — Der Kommissar
– Der Kommissar, Commented May 16, 2015 at 4:25
I posted the method call the other two methods. There is nothing higher than that now only because it doesnt work yet. IQueryable<T> data would be something like this List<MyClass> data @EBrown — imGreg
– imGreg, Commented May 16, 2015 at 4:28
And what would MyClass look like? What is _gridSettings? What is _defaultColumn? — Der Kommissar
– Der Kommissar, Commented May 16, 2015 at 4:29
To keep the example simple MyClass would just contain prop1 which is an int. _gridSettings is just an object that will tell me which column to order by asc or desc. defaultColumn is PropertyInfo of a column. — imGreg
– imGreg, Commented May 16, 2015 at 4:34

xanatos · Accepted Answer · 2015-05-16 06:10:36Z

This is what you asked for, I think... I've tested it and it seems to work.

// Caching of the reflection
private static readonly MethodInfo orderByMethod = GetOrderByMethod("OrderBy");
private static readonly MethodInfo orderByDescendingMethod = GetOrderByMethod("OrderByDescending");

private static IOrderedQueryable<TSource> ExpressionSort<TSource>(Order order, IQueryable<TSource> source, PropertyInfo property)
{
    // Compose the expression tree that represents the parameter to 
    // the predicate.

    // The expression you would use is source => source.Property,

    // The parameter of the lambda, source
    ParameterExpression sourceExpression = Expression.Parameter(typeof(TSource), "source");

    // Accessing the expression
    MemberExpression propertyExpression = Expression.Property(sourceExpression, property);

    // The full lambda expression. We don't need the 
    // Expression.Lambda<>, but still the keySelector will be an
    // Expression<Func<,>>, because Expression.Lambda does it 
    // authomatically. LambdaExpression is simply a superclass of 
    // all the Expression<Delegate>
    LambdaExpression keySelector = Expression.Lambda(propertyExpression, sourceExpression);

    // The OrderBy method we will be using, that we have cached
    // in some static fields
    MethodInfo method = order == Order.ASC ? orderByMethod : orderByDescendingMethod;

    // Adapted from Queryable.OrderBy (retrieved from the reference
    // source code), simply changed the way the OrderBy method is
    // retrieved to "method"
    return (IOrderedQueryable<TSource>)source.Provider.CreateQuery<TSource>(Expression.Call(null, method.MakeGenericMethod(new Type[]
    {
        typeof(TSource),
        property.PropertyType
    }), new Expression[]
    {
        source.Expression,
        Expression.Quote(keySelector)
    }));
}

private static MethodInfo GetOrderByMethod(string methodName)
{
    // Here I'm taking the long and more correct way to find OrderBy/
    // OrderByDescending: looking for a public static method with the
    // right name, with two generic arguments and that has the 
    // parameters related to those two generic arguments in a certain
    // way (they must be IQueryable<arg0> and Expression<Func<arg0,
    // arg1>>
    MethodInfo orderByMethod = (from x in typeof(Queryable).GetMethods(BindingFlags.Static | BindingFlags.Public)
                                where x.Name == methodName
                                let generics = x.GetGenericArguments()
                                where generics.Length == 2
                                let parameters = x.GetParameters()
                                where parameters.Length == 2 &&
                                    parameters[0].ParameterType == typeof(IQueryable<>).MakeGenericType(generics[0]) &&
                                    parameters[1].ParameterType == typeof(Expression<>).MakeGenericType(typeof(Func<,>).MakeGenericType(generics))
                                select x).Single();

    return orderByMethod;
}

Please don't ever use AsQueryable<>(). It doesn't do what you think, and it is totally useless outside unit testing and very specific use cases.

This is exactly what I wanted. I did not realize how complicated it was.
Also, it would be nice if you would post information that would explain why this works over the other.

Grax32 · Accepted Answer · 2015-05-16 12:28:15Z

You could use my OrderByString extension. https://www.nuget.org/packages/OrderByString/ It takes strings for sort parameters. The sort parameters strings can be comma-delimited lists of property names, such as "Prop1,Prop2" or it can include a sort order as in "Prop1 DESC, Prop2 ASC".

using OrderByExtensions;

public static IQueryable<T> OrderData<T>(IQueryable<T> data)
{
    try
    {
        Order order = Order.ASC;
        var result = Enum.TryParse<Order>(_gridSettings.SortOrder, true, out order);

        var sortColumn = _gridSettings.IsSearch ? _gridSettings.SortColumn : _defaultColumn;

        data = data.OrderBy(sortColumn + " " + _gridSettings.SortOrder.ToString());
    }
    catch (Exception ex)
    {
        log.WriteLog(MethodBase.GetCurrentMethod(), LogLevel.FATAL, ex);
    }
    return data;
}

OR

You could use the following GetExpressionForProperty method that returns the expected sort expression for OrderBy, OrderByDescending, ThenBy, or ThenByDescending.

private static IQueryable<T> ExpressionSort<T>(Order order, IQueryable<T> data, PropertyInfo property)
{
    Expression<Func<T, object>> propertyExpression = GetExpressionForProperty<T>(property);

    return order == Order.DESC ? data.OrderByDescending(propertyExpression) : data.OrderBy(propertyExpression);
}

static Expression<Func<TSource, object>> GetExpressionForProperty<TSource>(PropertyInfo propertyInfo)
{
    var param = Expression.Parameter(typeof(TSource));

    return Expression.Lambda<Func<TSource, object>>(
        Expression.Convert(
            Expression.Property(param, propertyInfo),
            typeof(object)
        )
        , param);
}

Community · Accepted Answer · 2017-05-23 12:16:52Z

0

Try using Expression.Convert. Here's a similar question that may give you some more guidance:

Expression of type 'System.Int32' cannot be used for return type 'System.Object'

edited May 23, 2017 at 12:16

CommunityBot

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answered May 16, 2015 at 3:26

John Hodge

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1 Comment

imGreg Over a year ago

I did see that answer there but I did not how to apply that answer to my code. I dont know what to put into Func<this part,bool>

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