How to use Generic AggregateFunction with nullalbe field ?

[Cyril]

Hi,

I want to adapt a generic aggregate function to deal with null.
I tried that:

    public MainPage()
    {
        InitializeComponent();
        List<Item> items = new List<Item>();
        for (int i = 0; i < 10; i++)
        {
            if (i % 2 == 0)
            {
                items.Add(new Item() { ValueDouble = 1, ValueInt = null });
            }
            else
            {
                items.Add(new Item() { ValueDouble = null, ValueInt = 2 });
            }
        }
        this.RadGridView1.ItemsSource = items;
        this.RadGridView1.Columns[0].AggregateFunctions.Add(new MyAggregateFunction() { SourceField = "ValueDouble" });
        this.RadGridView1.Columns[0].AggregateFunctions.Add(new MyAggregateFunction() { SourceField = "ValueInt" });
    }
}

public class Item
{
    public double? ValueDouble { get; set; }
    public int? ValueInt { get; set; }
}

And then

public class MyAggregateFunction : EnumerableSelectorAggregateFunction

    {

        protected override string AggregateMethodName

        {

            get

            {

                return "MyAggregateMethod";

            }

        }

 

        protected override Type ExtensionMethodsType

        {

            get

            {

                return typeof(MyAggregates);

            }

        }

    }

 

    public class MyAggregates

    {

        public static double MyAggregateMethod<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, TResult> selector)

        {

                              // Some logic
                              return 0.0;

        }

    }

But I got an exception:

Aucune méthode générique 'MyAggregateMethod' sur le type 'CustomAggregateFunctionSL.MyAggregates' n'est compatible avec les arguments de type et les arguments fournis. Aucun argument de type ne doit être fourni si la méthode n'est pas générique. 

In fact, it is not only with nullable type, but with all the base type, int, double...
So why the RadGridView didn't find the MyAggregateMethod ?
It seems that it has the right prototype, I don't get it at all.

[Rossen Hristov]

Hello Cyril,

I am afraid that only TSource can be generic. The result cannot be generic. It has to be specified explicitly:

public static double MyAggregateMethod<TSource>(IEnumerable<TSource> source
    , Func<TSource, double?> selector)
{
    // Some logic
    return 0.0;
}

I hope this helps.

All the best,
Ross
the Telerik team

[Cyril]

Ok, but can I make a function which will accept all base type (int, double...) and all nullable type (int?, double?...).
Maybe something like

 MyAggregateMethod<TSource>(IEnumerable<TSource> source

    , Func<TSource, object?> selector)

Is this possible?

[Rossen Hristov]

Hello Cyril,

I am afraid that not. See, we look for a static method by using reflection. We look for a method that is called "Something", that has specific type arguments and specific arguments. All of this depends on the particular member that the function will be applied over. So if the member is double? we will look for a method whose second argument is exactly Func<TSource, double?> selector.

We need this strong typing so our data engine can work correctly when locating and then executing these functions. If we could make the second parameter generic as well, we would have done this, trust me. There simply isn't a way for us to do it that way.

Thank you for your understanding.

Regards,
Ross
the Telerik team

[Cyril]

I understand that. The problem is that I receive data from outside, and it could be of any type, and I have to be able to used a custom aggregate.
I think I will have to list every possible case...

Thanks for your time!

[Rossen Hristov]

Hi Cyril,

I am afraid that you will have. I also wish that was not the case.

Anyway, I will let you know if I manage to think of some kind of "dirty workaround hack", but I can't really promise that there exists one.

All the best,
Ross
the Telerik team

[Cyril]

FYI, here the kind of thing I have in mind:

public static class DGAggregates
    {
        private static double doGenericSum<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, TResult> selector)
        {
            if (!source.Any<TSource>())
                return 0;
            else
            {
                var values = (from i in source select selector(i)).ToList();
                double result = 0;
                foreach (var value in values)
                {
                    double toAdd  = 0;
                    double.TryParse(value.ToString(), out toAdd);
                    result += toAdd;
                }
                //var result = values.Cast<Double>().Sum();
                return result;
            }
        }
        public static double DGSum<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, TResult> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, double> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, double?> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, float?> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, float> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, decimal?> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, decimal> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, int> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, int?> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, bool> selector)
        {
            return doGenericSum(source, selector);
        }
        public static double DGSum<TSource>(IEnumerable<TSource> source, Func<TSource, bool?> selector)
        {
            return doGenericSum(source, selector);
        }
    }