casacore::TableExprIdAggr Class Reference

The Table Expression Selection id used with aggregation. More...

#include <TableExprIdAggr.h>

Inheritance diagram for casacore::TableExprIdAggr:

Public Member Functions
	TableExprIdAggr (const CountedPtr< TableExprGroupResult > &result)
	Construct it from the aggregation results.
const TableExprGroupResult &	result () const
	Get out the aggregation result object.
uInt	getMagicValue () const
	Get the magic value (to check if it correct).
Static Public Member Functions
static const TableExprIdAggr &	cast (const TableExprId &id)
	Cast a TableExprId object to TableExprIdAggr.
Private Attributes
uInt	itsMagicValue
CountedPtr< TableExprGroupResult >	itsResult

Detailed Description

The Table Expression Selection id used with aggregation.

Intended use:

Public interface

Review Status

Reviewed By:: UNKNOWN
Date Reviewed:: before2004/08/25
Test programs:: tExprGroup

Synopsis

This class provides the user the ability to identify the data objects to test in a TaQL expression using aggregate functions.
It adds a TableExprGroupResult object to the TableExprId class which is used by the various classes derived from TableExprGroupFuncBase to get or evaluate the aggregated value. An aggregated value can be determined in two ways:

An immediate aggregate function has calculated its value in its apply function. Each group has a TableExprGroupFuncSet containing the values of all immediate aggregate functions of that group. A vector of these objects is part of of TableExprGroupResult and is used by the TableExprAggrNode(Array) get functions to return the correct value.
A lazy aggregate function calculates the value as part of its get function. It uses the vector of TableExprId objects in TableExprGroupResult to know which rows (or records) belong to which group. Note that UDF aggregate functions are always lazy.

TableExprIdAggr contains a static function to (statically) cast a TableExprId object to TableExprIdAggr. A magic value is used to check that the cast is valid.
No dynamic_cast is used, because it requires TableExprId to contain virtual functions making the object larger. TaQL can hold quite large vectors of TableExprId objects, so such overhead is unacceptably large.