Progress® Telerik® Reporting R2 2021

IAggregateFunction Interface

Provides custom (user-defined) implementation for aggregate function.

Namespace:  Telerik.Reporting.Expressions
Assembly:  Telerik.Reporting (in Telerik.Reporting.dll)

Syntax

C#

VB

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public interface IAggregateFunction

Public Interface IAggregateFunction

The IAggregateFunction type exposes the following members.

Methods

	Name	Description
	Accumulate	Accumulates the passed values in the aggregate.
	GetValue	Gets the value that the aggregate instance keeps currently accumulated.
	Init	Initializes the aggregate function instance. Implement to set the aggregate in its initial state ready to accumulate and merge values.
	Merge	Merges another instance of the same aggregate function into the current instance. Implement this method to allow the reporting engine to merge the two resulting aggregates coming from two subsets of the aggregated data source rows.

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Remarks

Implement this interface to provide custom logic when aggregating values over a set of rows from the data source. Apply the AggregateFunctionAttribute class to the aggregate implementation in order to set the name and description of the aggregate function. If no AggregateFunctionAttribute is defined, the name of the aggregate function is the name of the actual type that implements the IAggregateFunction interface. The word "Aggregate" is trimmed from the type name if it ends with it.

Examples

This example shows how to implement user-defined aggregate.

C#

VB

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[AggregateFunction(Description = "Concatenation aggregate. Output: (value1, value2, ...)", Name = "Concatenate")]
class ConcatenateAggregate : IAggregateFunction
{
    string result;

    public void Accumulate(object[] values)
    {
        // The aggregate function expects one parameter
        object value = values[0];

        // null values are not aggregated
        if (null == value)
        {
            return;
        }

        // The actual accumulation
        if (this.result.Length > 0)
        {
            result += ", ";
        }
        this.result += value.ToString();
    }

    public object GetValue()
    {
        return string.Format("({0})", this.result);
    }

    public void Init()
    {
        // Add aggregate function initialization code here if needed
        this.result = string.Empty;
    }

    public void Merge(IAggregateFunction aggregateFunction)
    {
        ConcatenateAggregate aggregate = (ConcatenateAggregate)aggregateFunction;

        if (aggregate.result.Length > 0)
        {
            if (this.result.Length > 0)
            {
                result += ", ";
            }
            this.result += aggregate.result;
        }
    }
}

<AggregateFunction(Description:="Concatenation aggregate. Output: (value1, value2, ...)", Name:="Concatenate")> _
Class ConcatenateAggregate
    Implements IAggregateFunction
    Private result As String

    Public Sub Accumulate(ByVal values As Object()) Implements IAggregateFunction.Accumulate
        ' The aggregate function expects one parameter
        Dim value As Object = values(0)

        ' null values are not aggregated
        If value Is Nothing Then
            Return
        End If

        ' The actual accumulation
        If Me.result.Length > 0 Then
            result += ", "
        End If
        Me.result += value.ToString()
    End Sub

    Public Function GetValue() As Object Implements IAggregateFunction.GetValue
        Return String.Format("({0})", Me.result)
    End Function

    Public Sub Init() Implements IAggregateFunction.Init
        ' Add aggregate function initialization code here if needed
        Me.result = String.Empty
    End Sub

    Public Sub Merge(ByVal aggregateFunction As IAggregateFunction) Implements IAggregateFunction.Merge
        Dim aggregate As ConcatenateAggregate = DirectCast(aggregateFunction, ConcatenateAggregate)

        If aggregate.result.Length > 0 Then
            If Me.result.Length > 0 Then
                result += ", "
            End If
            Me.result += aggregate.result
        End If
    End Sub
End Class

Version Information

Supported in: 1.0.1

See Also

Reference

Telerik.Reporting.Expressions Namespace