HDF5Record.h

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//# HDF5Record.h: A class to write/read a record into HDF5
//# Copyright (C) 2008
//# Associated Universities, Inc. Washington DC, USA.
//#
//# This library is free software; you can redistribute it and/or modify it
//# under the terms of the GNU Library General Public License as published by
//# the Free Software Foundation; either version 2 of the License, or (at your
//# option) any later version.
//#
//# This library is distributed in the hope that it will be useful, but WITHOUT
//# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
//# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
//# License for more details.
//#
//# You should have received a copy of the GNU Library General Public License
//# along with this library; if not, write to the Free Software Foundation,
//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
//#
//# Correspondence concerning AIPS++ should be addressed as follows:
//#        Internet email: aips2-request@nrao.edu.
//#        Postal address: AIPS++ Project Office
//#                        National Radio Astronomy Observatory
//#                        520 Edgemont Road
//#                        Charlottesville, VA 22903-2475 USA
//#
//# $Id: HDF5Record.h 20615 2009-06-09 02:16:01Z Malte.Marquarding $

#ifndef CASA_HDF5RECORD_H
#define CASA_HDF5RECORD_H

//# Includes
#include <casa/HDF5/HDF5Object.h>
#include <casa/HDF5/HDF5DataType.h>
#include <casa/Containers/Record.h>

namespace casa { //# NAMESPACE CASA - BEGIN

  // <summary>
  // A class to write/read a record into HDF5.
  // </summary>

  // <use visibility=export>

  // <reviewed reviewer="" date="" tests="tHDF5Record.cc">
  // </reviewed>

  // <prerequisite>
  //   <li> <a href="http://hdf.ncsa.uiuc.edu">HDF5 system</a>
  //   <li> <linkto class=Record>class Record</linkto>
  // </prerequisite>

  // <synopsis>
  // This class has a static function to write a Record (or TableRecord)
  // into an HDF5 file by storing it as attributes for the given group.
  // Another static function can read back the Record.
  // It can handle all types of fields in a record.
  // <br>
  // A few remarks:
  // <ul>
  //  <li> When writing the record, it first deletes all attributes of the group
  //   to be sure that the group's attributes only contain the record.
  //  <li> An AIPS++ Record is a recursive structure, so it is written as nested
  //   groups. The name of a subgroup is the name of the subrecord.
  // <li> HDF5 cannot deal with empty arrays. Therefore they are written as
  //   a special compound type holding the rank and type of the empty array.
  // <li> HDF5 cannot hold empty fixed length strings. This is solved by
  //   storing an empty string with the special value <tt>__empty__</tt>.
  // </ul>
  // </synopsis> 

  // <motivation>
  // Record is a very important class in AIPS++ images, so it has to be
  // possible to read and write them from/to HDF5.
  // </motivation>

  class HDF5Record
  {
  public: 
    // Read a record from the attributes of the given group.
    // Nested records are read back correctly.
    // An empty record is returned if the group does not exist.
    static Record readRecord (const HDF5Object& parentHid,
                              const String& groupName);

    // Write the record as attributes of a group of the given parent.
    // Nested records are written as nested groups.
    // The group is deleted first if it already exists.
    static void writeRecord (const HDF5Object& parentHid,
                             const String& recordName,
                             const RecordInterface& rec);

    // Remove the record (i.e. group) from the given parent.
    // Nothing is done if the record does not exist.
    static void remove (const HDF5Object& parentHid,
                        const String& recordName);

    // Read back a (nested) record.
    static Record doReadRecord (hid_t parentHid);

  private:
    // Read a scalar value and add it to the record.
    static void readScalar (hid_t attrId, hid_t dtid,
                            const String& name, RecordInterface& rec);

    // Read an array value and add it to the record.
    static void readArray (hid_t attrId, hid_t dtid, const IPosition&,
                           const String& name, RecordInterface& rec);

    // Read a scalar string from an attribute and add it to the record.
    static void readScaString (hid_t attrId, Int sz,
                               const String& name, RecordInterface& rec);

    // Read a array of strings from an atrribute and add it to the record.
    static void readArrString (hid_t attrId, const IPosition&,
                               const String& name, RecordInterface& rec);

    // Read a field containing an empty array.
    static void readEmptyArray (hid_t attrId,
                                const String& name, RecordInterface& rec);

    // Read a field containing a scalar of fixed length.
    template<typename T>
    static void readSca (hid_t attrId, const String& name,
                         RecordInterface& rec)
    {
      T value;
      HDF5DataType dtype((T*)0);
      read (attrId, &value, dtype);
      rec.define (name, value);
    }

    // Read a field containing an array of fixed length elements.
    template<typename T>
    static void readArr (hid_t attrId, const IPosition& shape,
                         const String& name,
                         RecordInterface& rec)
    {
      Array<T> value(shape);
      HDF5DataType dtype((T*)0);
      read (attrId, value.data(), dtype);
      rec.define (name, value);
    }

    // Read fixed length values from an attribute (scalar and array).
    static void read (hid_t attrId, void* value,
                      const HDF5DataType& dtype);

    // Write a (nested) record.
    static void doWriteRecord (const HDF5Object& groupHid,
                               const RecordInterface& rec);

    // Write a fixed length scalar value as attribute.
    static void writeScalar (hid_t parentHid, const String& name,
                             const void* value,
                             const HDF5DataType& dtype);

    // Write an array of fixed length values as attribute.
    static void writeArray (hid_t parentHid, const String& name,
                            const void* value, const IPosition& shape,
                            const HDF5DataType& dtype);

    // Write a scalar string as attribute.
    // HDF5 cannot handle empty strings, so for empty strings a special
    // value is written.
    static void writeScaString (hid_t parentHid, const String& name,
                                const String& value);

    // Write an array of strings as attribute.
    // HDF5 cannot handle empty strings, so for empty strings a special
    // value is written.
    static void writeArrString (hid_t parentHid, const String& name,
                                const Array<String>& value);

    // Write a field containing an empty array.
    static void writeEmptyArray (hid_t groupHid, const String& name,
                                 Int rank, DataType dtype);

    // Write a field containing a fixed length scalar value.
    template<typename T>
    static void writeSca (hid_t parentHid, const String& name,
                          const RecordInterface& rec, Int i)
    {
      T value;
      rec.get (i, value);
      HDF5DataType dtype((T*)0);
      writeScalar (parentHid, name, &value, dtype);
    }

    // Write a field containing an array of fixed length elements.
    template<typename T>
    static void writeArr (hid_t parentHid, const String& name,
                          const RecordInterface& rec, Int i)
    {
      Array<T> value;
      rec.get (i, value);
      HDF5DataType dtype((T*)0);
      writeArray (parentHid, name, value.data(), value.shape(), dtype);
    }

  };

}

#endif