00001 //# TableExprIdAggr.h: The Table Expression Selection id used with aggregation 00002 //# Copyright (C) 2013 00003 //# Associated Universities, Inc. Washington DC, USA. 00004 //# 00005 //# This library is free software; you can redistribute it and/or modify it 00006 //# under the terms of the GNU Library General Public License as published by 00007 //# the Free Software Foundation; either version 2 of the License, or (at your 00008 //# option) any later version. 00009 //# 00010 //# This library is distributed in the hope that it will be useful, but WITHOUT 00011 //# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 00012 //# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public 00013 //# License for more details. 00014 //# 00015 //# You should have received a copy of the GNU Library General Public License 00016 //# along with this library; if not, write to the Free Software Foundation, 00017 //# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA. 00018 //# 00019 //# Correspondence concerning AIPS++ should be addressed as follows: 00020 //# Internet email: aips2-request@nrao.edu. 00021 //# Postal address: AIPS++ Project Office 00022 //# National Radio Astronomy Observatory 00023 //# 520 Edgemont Road 00024 //# Charlottesville, VA 22903-2475 USA 00025 //# 00026 //# 00027 //# $Id: TableExprId.h 21403 2013-12-03 20:51:02Z gervandiepen $ 00028 00029 00030 #ifndef TABLES_TABLEEXPRIDAGGR_H 00031 #define TABLES_TABLEEXPRIDAGGR_H 00032 00033 //# Includes 00034 #include <casacore/casa/aips.h> 00035 #include <casacore/tables/TaQL/TableExprId.h> 00036 #include <casacore/tables/TaQL/ExprGroup.h> 00037 #include <casacore/casa/Utilities/CountedPtr.h> 00038 #include <casacore/casa/Utilities/Assert.h> 00039 #include <casacore/casa/Exceptions/Error.h> 00040 #include <casacore/casa/stdvector.h> 00041 00042 namespace casacore { //# NAMESPACE CASACORE - BEGIN 00043 00044 // <summary> 00045 // The Table Expression Selection id used with aggregation 00046 // </summary> 00047 00048 // <use visibility=export> 00049 00050 // <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="tExprGroup"> 00051 // </reviewed> 00052 00053 // <synopsis> 00054 // This class provides the user the ability to identify the data objects 00055 // to test in a TaQL expression using aggregate functions. 00056 // <br> 00057 // It adds a TableExprGroupResult object to the TableExprId class which 00058 // is used by the various classes derived from TableExprGroupFuncBase 00059 // to get or evaluate the aggregated value. 00060 // An aggregated value can be determined in two ways: 00061 // <ul> 00062 // <li> An immediate aggregate function has calculated its value in its 00063 // <src>apply</src> function. 00064 // Each group has a TableExprGroupFuncSet containing the values 00065 // of all immediate aggregate functions of that group. 00066 // A vector of these objects is part of of TableExprGroupResult 00067 // and is used by the TableExprAggrNode(Array) <src>get</src> functions 00068 // to return the correct value. 00069 // <li> A lazy aggregate function calculates the value as part of its 00070 // <src>get</src> function. It uses the vector of TableExprId objects 00071 // in TableExprGroupResult to know which rows (or records) belong to 00072 // which group. Note that UDF aggregate functions are always lazy. 00073 // </ul> 00074 // TableExprIdAggr contains a static function to (statically) cast a 00075 // TableExprId object to TableExprIdAggr. A magic value is used to check 00076 // that the cast is valid. 00077 // <br>No dynamic_cast is used, because it requires TableExprId to contain 00078 // virtual functions making the object larger. TaQL can hold quite large 00079 // vectors of TableExprId objects, so such overhead is unacceptably large. 00080 // </synopsis> 00081 00082 // <motivation> 00083 // This class makes it possible to retrieve aggregated values using the 00084 // standard <src>get</src> functions taking an TableExprId. 00085 // </motivation> 00086 00087 class TableExprIdAggr: public TableExprId 00088 { 00089 public: 00090 // Construct it from the aggregation results. 00091 explicit TableExprIdAggr (const CountedPtr<TableExprGroupResult>& result) 00092 : itsMagicValue (0xabababab), 00093 itsResult (result) 00094 {} 00095 00096 // Get out the aggregation result object. 00097 const TableExprGroupResult& result() const 00098 { return *itsResult; } 00099 00100 // Get the magic value (to check if it correct). 00101 uInt getMagicValue() const 00102 { return itsMagicValue; } 00103 00104 // Cast a TableExprId object to TableExprIdAggr. It check if the cast 00105 // if correct by checking the magic value. 00106 static const TableExprIdAggr& cast (const TableExprId& id) 00107 { 00108 const TableExprIdAggr& idAggr = reinterpret_cast<const TableExprIdAggr&>(id); 00109 AlwaysAssert (idAggr.getMagicValue() == 0xabababab, AipsError); 00110 return idAggr; 00111 } 00112 00113 private: 00114 uInt itsMagicValue; 00115 CountedPtr<TableExprGroupResult> itsResult; 00116 }; 00117 00118 00119 } //# NAMESPACE CASACORE - END 00120 00121 #endif