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/* flint_alltermslist.h: A termlist containing all terms in 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_ALLTERMSLIST_H
#define XAPIAN_INCLUDED_FLINT_ALLTERMSLIST_H
#include "alltermslist.h"
#include "flint_database.h"
#include "flint_postlist.h"
class FlintCursor;
class FlintAllTermsList : public AllTermsList {
/// Copying is not allowed.
FlintAllTermsList(const FlintAllTermsList &);
/// Assignment is not allowed.
void operator=(const FlintAllTermsList &);
/// Keep a reference to our database to stop it being deleted.
Xapian::Internal::RefCntPtr<const FlintDatabase> database;
/** A cursor which runs through the postlist table reading termnames from
* the keys.
*/
FlintCursor * cursor;
/// The approximate number of terms in this list.
Xapian::termcount approx_size;
/// The termname at the current position.
string current_term;
/// The prefix to restrict the terms to.
string prefix;
/** The term frequency of the term at the current position.
*
* If this value is zero, then we haven't read the term frequency or
* collection frequency for the current term yet. We need to call
* read_termfreq_and_collfreq() to read these.
*/
mutable Xapian::termcount termfreq;
/// The collection frequency of the term at the current position.
mutable Xapian::termcount collfreq;
/// Read and cache the term frequency and collection frequency.
void read_termfreq_and_collfreq() const;
public:
FlintAllTermsList(Xapian::Internal::RefCntPtr<const FlintDatabase> database_,
const string & prefix_)
: database(database_), prefix(prefix_), termfreq(0) {
// The number of entries in the postlist table will be the number of
// terms, probably plus some extra entries for chunked posting lists,
// plus 1 for the metainfo key (unless the table is completely empty).
// FIXME : this can badly overestimate (it could be several times too
// large) - perhaps keep track of the number of terms (or number of
// extra chunks) and store this along with the last_docid and
// total_doclen? (Mind you, not sure this value is ever used, but
// we should really make the exact number of terms available somewhere
// in the API).
approx_size = database->postlist_table.get_entry_count();
if (approx_size) --approx_size;
cursor = database->postlist_table.cursor_get();
Assert(cursor); // The postlist table isn't optional.
// Position the cursor 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_lt(string("\x00\xff", 2));
} else {
cursor->find_entry_lt(pack_string_preserving_sort(prefix));
}
}
/// Destructor.
~FlintAllTermsList();
/** Returns the approximate size of the list.
*
* This is probably 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;
/** Returns the term frequency of the current term.
*
* Either next() or skip_to() must have been called before this
* method can be called.
*/
Xapian::doccount get_termfreq() const;
/** Returns the collection frequency of the current term.
*
* Either next() or skip_to() must have been called before this
* method can be called.
*/
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_ALLTERMSLIST_H */
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