Templated virtual column engine to map the data type of a table array. More...

#include <MappedArrayEngine.h>

Inheritance diagram for casa::MappedArrayEngine< VirtualType, StoredType >:

Public Member Functions
	MappedArrayEngine (const String &virtualColumnName, const String &storedColumnName)
	Construct an engine to map all arrays in a column.
	MappedArrayEngine (const Record &spec)
	Construct from a record specification as created by dataManagerSpec().
	~MappedArrayEngine ()
	Destructor is mandatory.
virtual String	dataManagerType () const
	Return the type name of the engine (i.e.
virtual String	dataManagerName () const
	Get the name given to the engine (is the virtual column name).
virtual Record	dataManagerSpec () const
	Record a record containing data manager specifications.
Static Public Member Functions
static String	className ()
	Return the name of the class.
static void	registerClass ()
	Register the class name and the static makeObject "constructor".
static DataManager *	makeObject (const String &dataManagerType, const Record &spec)
	Define the "constructor" to construct this engine when a table is read back.
Private Member Functions
	MappedArrayEngine (const MappedArrayEngine< VirtualType, StoredType > &)
	Copy constructor is only used by clone().
MappedArrayEngine< VirtualType, StoredType > &	operator= (const MappedArrayEngine< VirtualType, StoredType > &)
	Assignment is not needed and therefore forbidden (so it is made private and not implemented).
DataManager *	clone () const
	Clone the engine object.
virtual void	mapOnGet (Array< VirtualType > &array, const Array< StoredType > &stored)
	Copy the stored array to the virtual array.
virtual void	mapOnPut (const Array< VirtualType > &array, Array< StoredType > &stored)
	Copy the virtual array to the stored array.

Detailed Description

template<class VirtualType, class StoredType>
class casa::MappedArrayEngine< VirtualType, StoredType >

Templated virtual column engine to map the data type of a table array.

Intended use:

Public interface

Review Status

Reviewed By:: Gareth Hunt
Date Reviewed:: 94Nov17

Prerequisite

Synopsis

MappedArrayEngine is a virtual column engine which maps an array of one type to another type (without any scaling).

An engine object should be used for one column only, because the stored column name is part of the engine. If it would be used for more than one column, they would all share the same stored column. When the engine is bound to a column, it is checked if the name of that column matches the given virtual column name.

The engine can be used for a column containing any kind of array (thus direct or indirect, fixed or variable shaped)) as long as the virtual array can be stored in the stored array. Thus a fixed shaped virtual can use a variable shaped stored, but not vice versa. A fixed shape indirect virtual can use a stored with direct arrays.

Motivation

For precision it is sometimes needed to store the visibility data in a MeasurementSet in double precision. To be able to use other applications on such data, it is needed to map them to single precision.

Because the engine can serve only one column, it was possible to combine the engine and the column functionality in one class. This has been achieved using multiple inheritance. The advantage of this is that only one templated class is used, so less template instantiations are needed.

Example

    // Create the table description and 2 columns with indirect arrays in it.
    // The Int column will be stored, while the double will be
    // used as virtual.
    TableDesc tableDesc ("", TableDesc::Scratch);
    tableDesc.addColumn (ArrayColumnDesc<Int> ("storedArray"));
    tableDesc.addColumn (ArrayColumnDesc<double> ("virtualArray"));
   
    // Create a new table using the table description.
    SetupNewTable newtab (tableDesc, "tab.data", Table::New);
   
    // Create the array mapping engine to map from double to Int
    // and bind it to the double column.
    // Create the table.
    MappedArrayEngine<double,Int> mappingEngine("virtualArray",
                                                "storedArray", 10);
    newtab.bindColumn ("virtualArray", mappingEngine);
    Table table (newtab);
   
    // Store a 3-D array (with dim. 2,3,4) into each row of the column.
    // The shape of each array in the column is implicitly set by the put
    // function. This will also set the shape of the underlying Int array.
    ArrayColumn data (table, "virtualArray");
    Array<double> someArray(IPosition(4,2,3,4));
    someArray = 0;
    for (uInt i=0, i<10; i++) {          // table will have 10 rows
        table.addRow();
        data.put (i, someArray)
    }

Template Type Argument Requirements (VirtualType)

only suited for built-in numerics data types