root / tags / 1.0.8 / xapian-core / backends / flint / flint_synonym.h

/** @file flint_synonym.h
 * @brief Synonym data for a flint database.
 */
/* Copyright (C) 2005,2007 Olly Betts
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#ifndef XAPIAN_INCLUDED_FLINT_SYNONYM_H
#define XAPIAN_INCLUDED_FLINT_SYNONYM_H

#include <xapian/types.h>

#include "alltermslist.h"
#include "database.h"
#include "flint_table.h"
#include "omdebug.h"
#include "termlist.h"

#include <set>
#include <string>

class FlintSynonymTable : public FlintTable {
    /// The last term which was updated.
    mutable std::string last_term;

    /// The synonyms for the last term which was updated.
    mutable std::set<std::string> last_synonyms;

  public:
    /** Create a new FlintSynonymTable object.
     *
     *  This method does not create or open the table on disk - you
     *  must call the create() or open() methods respectively!
     *
     *  @param dbdir            The directory the flint database is stored in.
     *  @param readonly         true if we're opening read-only, else false.
     */
    FlintSynonymTable(std::string dbdir, bool readonly)
        : FlintTable(dbdir + "/synonym.", readonly, Z_DEFAULT_STRATEGY, true) { }

    // Merge in batched-up changes.
    void merge_changes();

    // Discard batched-up changes.
    void discard_changes() {
        last_term.resize(0);
        last_synonyms.clear();
    }

    /** Add a synonym for @a term.
     *
     *  If the synonym has already been added, no action is taken.
     */
    void add_synonym(const std::string & term, const std::string & synonym);

    /** Remove a synonym for @a term.
     *
     *  If the synonym doesn't exist, no action is taken.
     */
    void remove_synonym(const std::string & term, const std::string & synonym);

    /** Remove all synonyms for @a term.
     *
     *  If @a term has no synonyms, no action is taken.
     */
    void clear_synonyms(const std::string & term);

    /** Open synonym termlist for a term.
     *
     *  If @a term has no synonyms, NULL is returned.
     */
    TermList * open_termlist(const std::string & term);

    /** Override methods of FlintTable.
     *
     *  NB: these aren't virtual, but we always call them on the subclass in
     *  cases where it matters).
     *  @{
     */

    bool is_modified() const {
        return !last_term.empty() || FlintTable::is_modified();
    }

    void create_and_open(unsigned int blocksize) {
        // The synonym table is created lazily, but erase it in case we're
        // overwriting an existing database and it already exists.
        FlintTable::erase();
        FlintTable::set_block_size(blocksize);
    }

    void commit(flint_revision_number_t revision) {
        merge_changes();
        FlintTable::commit(revision);
    }

    void cancel() {
        discard_changes();
        FlintTable::cancel();
    }

    // @}
};

class FlintCursor;

class FlintSynonymTermList : public AllTermsList {
    /// Copying is not allowed.
    FlintSynonymTermList(const FlintSynonymTermList &);

    /// Assignment is not allowed.
    void operator=(const FlintSynonymTermList &);

    /// Keep a reference to our database to stop it being deleted.
    Xapian::Internal::RefCntPtr<const Xapian::Database::Internal> database;

    /** A cursor which runs through the synonym table reading termnames from
     *  the keys.
     */
    FlintCursor * cursor;

    /// The number of terms in this list.
    Xapian::termcount size;

    /// The prefix to restrict the terms to.
    string prefix;

  public:
    FlintSynonymTermList(Xapian::Internal::RefCntPtr<const Xapian::Database::Internal> database_,
                      FlintCursor * cursor_,
                      Xapian::termcount size_,
                      const string & prefix_)
            : database(database_), cursor(cursor_), size(size_), prefix(prefix_)
    {
        // Position the on the highest key before the first key we want, so
        // that the first call to next() will put us on the first key we want.
        if (prefix.empty()) {
            cursor->find_entry(string());
        } else {
            // Seek to the first key before one with the desired prefix.
            cursor->find_entry_lt(prefix);
        }
    }

    /// Destructor.
    ~FlintSynonymTermList();

    /** Returns the approximate size of the list.
     *
     *  This may be unused for this class.
     */
    Xapian::termcount get_approx_size() const;

    /** Returns the current termname.
     *
     *  Either next() or skip_to() must have been called before this
     *  method can be called.
     */
    string get_termname() const;

    /// Return the term frequency for the term at the current position.
    Xapian::doccount get_termfreq() const;

    /// Return the collection frequency for the term at the current position.
    Xapian::termcount get_collection_freq() const;

    /// Advance to the next term in the list.
    TermList * next();

    /// Advance to the first term which is >= tname.
    TermList * skip_to(const string &tname);

    /// True if we're off the end of the list
    bool at_end() const;
};

#endif // XAPIAN_INCLUDED_FLINT_SYNONYM_H