xapian-core/include/xapian/keymaker.h

   1 /** @file keymaker.h
   2  * @brief Build key strings for MSet ordering or collapsing.
   3  */
   4 /* Copyright (C) 2007,2009,2011,2013,2014,2015,2016 Olly Betts
   5  * Copyright (C) 2010 Richard Boulton
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public License as
   9  * published by the Free Software Foundation; either version 2 of the
  10  * License, or (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  20  */
  21
  22 #ifndef XAPIAN_INCLUDED_KEYMAKER_H
  23 #define XAPIAN_INCLUDED_KEYMAKER_H
  24
  25 #if !defined XAPIAN_IN_XAPIAN_H && !defined XAPIAN_LIB_BUILD
  26 # error "Never use <xapian/keymaker.h> directly; include <xapian.h> instead."
  27 #endif
  28
  29 #include <string>
  30 #include <vector>
  31
  32 #include <xapian/intrusive_ptr.h>
  33 #include <xapian/types.h>
  34 #include <xapian/visibility.h>
  35
  36 namespace Xapian {
  37
  38 class Document;
  39
  40 /** Virtual base class for key making functors. */
  41 class XAPIAN_VISIBILITY_DEFAULT KeyMaker
  42     : public Xapian::Internal::opt_intrusive_base {
  43     /// Don't allow assignment.
  44     void operator=(const KeyMaker &);
  45
  46     /// Don't allow copying.
  47     KeyMaker(const KeyMaker &);
  48
  49   public:
  50     /// Default constructor.
  51     KeyMaker() { }
  52
  53     /** Build a key string for a Document.
  54      *
  55      *  These keys can be used for sorting or collapsing matching documents.
  56      *
  57      *  @param doc      Document object to build a key for.
  58      */
  59     virtual std::string operator()(const Xapian::Document & doc) const = 0;
  60
  61     /** Virtual destructor, because we have virtual methods. */
  62     virtual ~KeyMaker();
  63
  64     /** Start reference counting this object.
  65      *
  66      *  You can hand ownership of a dynamically allocated KeyMaker
  67      *  object to Xapian by calling release() and then passing the object to a
  68      *  Xapian method.  Xapian will arrange to delete the object once it is no
  69      *  longer required.
  70      */
  71     KeyMaker * release() {
  72         opt_intrusive_base::release();
  73         return this;
  74     }
  75
  76     /** Start reference counting this object.
  77      *
  78      *  You can hand ownership of a dynamically allocated KeyMaker
  79      *  object to Xapian by calling release() and then passing the object to a
  80      *  Xapian method.  Xapian will arrange to delete the object once it is no
  81      *  longer required.
  82      */
  83     const KeyMaker * release() const {
  84         opt_intrusive_base::release();
  85         return this;
  86     }
  87 };
  88
  89 /** KeyMaker subclass which combines several values.
  90  *
  91  *  When the result is used for sorting, results are ordered by the first
  92  *  value.  In the event of a tie, the second is used.  If this is the same for
  93  *  both, the third is used, and so on.  If @a reverse is true for a value,
  94  *  then the sort order for that value is reversed.
  95  *
  96  *  When used for collapsing, the documents will only be considered equal if
  97  *  all the values specified match.  If none of the specified values are set
  98  *  then the generated key will be empty, so such documents won't be collapsed
  99  *  (which is consistent with the behaviour in the "collapse on a value" case).
 100  *  If you'd prefer that documents with none of the keys set are collapsed
 101  *  together, then you can set @a reverse for at least one of the values.
 102  *  Other than this, it isn't useful to set @a reverse for collapsing.
 103  */
 104 class XAPIAN_VISIBILITY_DEFAULT MultiValueKeyMaker : public KeyMaker {
 105     struct KeySpec {
 106         Xapian::valueno slot;
 107         bool reverse;
 108         std::string defvalue;
 109         KeySpec(Xapian::valueno slot_, bool reverse_,
 110                 const std::string & defvalue_)
 111                 : slot(slot_), reverse(reverse_), defvalue(defvalue_)
 112         {}
 113     };
 114     std::vector<KeySpec> slots;
 115
 116   public:
 117     MultiValueKeyMaker() { }
 118
 119     /** Construct a MultiValueKeyMaker from a pair of iterators.
 120      *
 121      *  The iterators must be a begin/end pair returning Xapian::valueno (or
 122      *  a compatible type) when dereferenced.
 123      */
 124     template <class Iterator>
 125     MultiValueKeyMaker(Iterator begin, Iterator end) {
 126         while (begin != end) add_value(*begin++);
 127     }
 128
 129     virtual std::string operator()(const Xapian::Document & doc) const;
 130
 131     /** Add a value slot to the list to build a key from.
 132      *
 133      *  @param slot     The value slot to add
 134      *  @param reverse  Adjust values from this slot to reverse their sort
 135      *                  order (default: false)
 136      *  @param defvalue Value to use for documents which don't have a value
 137      *                  set in this slot (default: empty).  This can be used
 138      *                  to make such documents sort after all others by
 139      *                  passing <code>get_value_upper_bound(slot) + "x"</code>
 140      *                  - this is guaranteed to be greater than any value in
 141      *                  this slot.
 142      */
 143     void add_value(Xapian::valueno slot, bool reverse = false,
 144                    const std::string & defvalue = std::string()) {
 145         slots.push_back(KeySpec(slot, reverse, defvalue));
 146     }
 147 };
 148
 149 }
 150
 151 #endif // XAPIAN_INCLUDED_KEYMAKER_H