Accesing column name on which aggregate function was applied

[Manoj]

Hi,

I have a custome aggregate function defined as follows. I would like to access the column name on which this particular function is being called from so that the function can act on that particular column. How can that be done? Currently I have hard-coded the column name('Score') which I do not want to do.

class Summation : AggregateFunction<BindableDynamicDictionary, int>
    {
        public Summation()
        {
            this.AggregationExpression = items => FindSum(items);

        }

        private int FindSum(IEnumerable<BindableDynamicDictionary> source)
        {

            var itemCount = source.Count();
            int sum = 0;
            if (itemCount >= 1)
            {
                var values = source.Select(i => i["Score"]);

                foreach (int str in values)
                {
                    sum = sum + str;
                }
            }

            return sum;
        }
    }

Thanks

[Dimitrina]

Hello,

I am afraid the generic aggregate function does not hold a reference on what the invoking column is and such an information is not available.

Regards,
Dimitrina
Telerik

 

 

[Manoj]

Is there any other Aggregate function available which holds this reference?
Your documentation to generic aggregate functions returns a 404 page not found error :
http://docs.telerik.com/devtools/wpf/api/html/allmembers_t_telerik_windows_data_aggregatefunction_2.htm

Thanks.

[Dimitrina]

Hello,

I apologize for this invalid link presented in our documentation after the recent migration of the help. I will resolve it, meanwhile the correct link is:
http://docs.telerik.com/devtools/wpf/api/html/t_telerik_windows_data_aggregatefunction_2.htm

As it turns out, there is not such a function, all the built-in ones inherit from AggregateFunction.

Regards,
Dimitrina
Telerik

 

 

[Manoj]

I am lost now. As I mentioned, all the columns and the type of aggregation are determined by the user at run-time.
I cannot hard code the column value on the aggregate functions.
Is there any other way I can achieve this functionality? Also curious how the inbuilt functions like count or average work without predetermined column name.
Any help would be appreciated!

Thanks!

[Dimitrina]

Hello,

You can also refer to our Source Code available for download from your account. The aggregate functions are presented under path ..\\Core\Data.

As to the question on how the AverageFunction knows the property to calculate on, it will be done based on the DataMemberBinding specified. This is the respective code involved:

private void SetSourceFieldToAggregateFunctionsIfNeeded()
{
    foreach (var selectorFunction in this.AggregateFunctions.OfType<EnumerableSelectorAggregateFunction>()
                                         .Where(f => f.SourceField == null))
    {
        selectorFunction.SourceField = this.GetDataMemberName();
    }
}
- - - -
public static string GetDataMemberName(this IDataFieldDescriptor descriptor)
{
    var name = string.Empty;
    if (descriptor != null)
    {
        var dataBinding = descriptor.DataMemberBinding;

        name = BindingToExpressionHelper.ExtractNameFromBinding(dataBinding, descriptor.ItemType);
        if (string.IsNullOrEmpty(name))
        {
            name = ExtractNameFromUniqueName(descriptor);
        }
    }

    return name;
}

Regards,
Dimitrina
Telerik