Xapian::ValuePostingSource Class Reference

A posting source which generates weights from a value slot. More...

#include <postingsource.h>

Inheritance diagram for Xapian::ValuePostingSource:

Collaboration diagram for Xapian::ValuePostingSource:

List of all members.

Public Member Functions

ValuePostingSource (Xapian::valueno slot_)

Construct a ValuePostingSource.

Xapian::doccount get_termfreq_min () const

A lower bound on the number of documents this object can return.

Xapian::doccount get_termfreq_est () const

An estimate of the number of documents this object can return.

Xapian::doccount get_termfreq_max () const

An upper bound on the number of documents this object can return.

void next (Xapian::weight min_wt)

Advance the current position to the next matching document.

void skip_to (Xapian::docid min_docid, Xapian::weight min_wt)

Advance to the specified docid.

bool check (Xapian::docid min_docid, Xapian::weight min_wt)

Check if the specified docid occurs.

bool at_end () const

Return true if the current position is past the last entry in this list.

Xapian::docid get_docid () const

Return the current docid.

void init (const Database &db_)

Set this PostingSource to the start of the list of postings.

Protected Attributes

Xapian::Database db

The database we're reading values from.

Xapian::valueno slot

The slot we're reading values from.

Xapian::ValueIterator value_it

Value stream iterator.

bool started

Flag indicating if we've started (true if we have).

Xapian::doccount termfreq_min

A lower bound on the term frequency.

Xapian::doccount termfreq_est

An estimate of the term frequency.

Xapian::doccount termfreq_max

An upper bound on the term frequency.

Detailed Description

A posting source which generates weights from a value slot.

This is a base class for classes which generate weights using values stored in the specified slot. For example, ValueWeightPostingSource uses sortable_unserialise to convert values directly to weights.

The upper bound on the weight returned is set to DBL_MAX. Subclasses should call set_maxweight() in their init() methods after calling ValuePostingSource::init() if they know a tighter bound on the weight.

Definition at line 345 of file postingsource.h.

Constructor & Destructor Documentation

Xapian::ValuePostingSource::ValuePostingSource ( Xapian::valueno slot_ )

Construct a ValuePostingSource.

Parameters:

slot_

The value slot to read values from.

Definition at line 112 of file postingsource.cc.

Member Function Documentation

bool Xapian::ValuePostingSource::at_end ( ) const [virtual]

Return true if the current position is past the last entry in this list.

At least one of next(), skip_to() or check() will be called before this method is first called.

Implements Xapian::PostingSource.

Definition at line 189 of file postingsource.cc.

References db, slot, started, value_it, and Xapian::Database::valuestream_end().

Referenced by DEFINE_TESTCASE(), and Xapian::ValueWeightPostingSource::get_weight().

bool Xapian::ValuePostingSource::check	(	Xapian::docid	did,
		Xapian::weight	min_wt
	)			`[virtual]`

Check if the specified docid occurs.

The caller is required to ensure that the specified document id did actually exists in the database. If it does, it must move to that document id, and return true. If it does not, it may either:

return true, having moved to a definite position (including "at_end"), which must be the same position as skip_to() would have moved to.

or

return false, having moved to an "indeterminate" position, such that a subsequent call to next() or skip_to() will move to the next matching position after did.

Generally, this method should act like skip_to() and return true if that can be done at little extra cost.

Otherwise it should simply check if a particular docid is present, returning true if it is, and false if it isn't.

The default implementation calls skip_to() and always returns true.

Xapian will always call init() on a PostingSource before calling this for the first time.

Note: in the case of a multi-database search, the docid specified is the docid in the single subdatabase relevant to this posting source. See the init() method for details.

Parameters:

	did	The document id to check.
	min_wt	The minimum weight contribution that is needed (this is just a hint which subclasses may ignore).

Reimplemented from Xapian::PostingSource.

Reimplemented in Xapian::DecreasingValueWeightPostingSource.

Definition at line 171 of file postingsource.cc.

References Xapian::ValueIterator::check(), db, Xapian::PostingSource::get_maxweight(), slot, started, value_it, Xapian::Database::valuestream_begin(), and Xapian::Database::valuestream_end().

Referenced by DEFINE_TESTCASE().

Xapian::docid Xapian::ValuePostingSource::get_docid ( ) const [virtual]

Return the current docid.

This method may assume that it will only be called when there is a "current document". See get_weight() for details.

Note: in the case of a multi-database search, the returned docid should be in the single subdatabase relevant to this posting source. See the init() method for details.

Implements Xapian::PostingSource.

Definition at line 195 of file postingsource.cc.

References Xapian::ValueIterator::get_docid(), and value_it.

Referenced by DEFINE_TESTCASE(), and Xapian::DecreasingValueWeightPostingSource::skip_if_in_range().

Xapian::doccount Xapian::ValuePostingSource::get_termfreq_est ( ) const [virtual]

An estimate of the number of documents this object can return.

It must always be true that:

get_termfreq_min() <= get_termfreq_est() <= get_termfreq_max()

Xapian will always call init() on a PostingSource before calling this for the first time.

Implements Xapian::PostingSource.

Definition at line 124 of file postingsource.cc.

References termfreq_est.

Referenced by DEFINE_TESTCASE().

Xapian::doccount Xapian::ValuePostingSource::get_termfreq_max ( ) const [virtual]

An upper bound on the number of documents this object can return.

Xapian will always call init() on a PostingSource before calling this for the first time.

Implements Xapian::PostingSource.

Definition at line 130 of file postingsource.cc.

References termfreq_max.

Referenced by DEFINE_TESTCASE().

Xapian::doccount Xapian::ValuePostingSource::get_termfreq_min ( ) const [virtual]

A lower bound on the number of documents this object can return.

Xapian will always call init() on a PostingSource before calling this for the first time.

Implements Xapian::PostingSource.

Definition at line 118 of file postingsource.cc.

References termfreq_min.

Referenced by DEFINE_TESTCASE().

void Xapian::ValuePostingSource::init ( const Database & db ) [virtual]

Set this PostingSource to the start of the list of postings.

This is called automatically by the matcher prior to each query being processed.

If a PostingSource is used for multiple searches, init() will therefore be called multiple times, and must handle this by using the database passed in the most recent call.

Parameters:

db

The database which the PostingSource should iterate through.

Note: the database supplied to this method must not be modified: in particular, the reopen() method should not be called on it.

Note: in the case of a multi-database search, a separate PostingSource will be used for each database (the separate PostingSources will be obtained using clone()), and each PostingSource will be passed one of the sub-databases as the db parameter here. The db parameter will therefore always refer to a single database. All docids passed to, or returned from, the PostingSource refer to docids in that single database, rather than in the multi-database.

Implements Xapian::PostingSource.

Reimplemented in Xapian::ValueWeightPostingSource, Xapian::DecreasingValueWeightPostingSource, and Xapian::ValueMapPostingSource.

Definition at line 201 of file postingsource.cc.

References db, Xapian::Database::get_doccount(), Xapian::Database::get_value_freq(), Xapian::PostingSource::set_maxweight(), slot, started, termfreq_est, termfreq_max, and termfreq_min.

void Xapian::ValuePostingSource::next ( Xapian::weight min_wt ) [virtual]

Advance the current position to the next matching document.

The PostingSource starts before the first entry in the list, so next() must be called before any methods which need the context of the current position.

Xapian will always call init() on a PostingSource before calling this for the first time.

Parameters:

min_wt

The minimum weight contribution that is needed (this is just a hint which subclasses may ignore).

Implements Xapian::PostingSource.

Reimplemented in Xapian::DecreasingValueWeightPostingSource.

Definition at line 136 of file postingsource.cc.

References db, Xapian::PostingSource::get_maxweight(), slot, started, value_it, Xapian::Database::valuestream_begin(), and Xapian::Database::valuestream_end().

Referenced by DEFINE_TESTCASE().

void Xapian::ValuePostingSource::skip_to	(	Xapian::docid	did,
		Xapian::weight	min_wt
	)			`[virtual]`

Advance to the specified docid.

If the specified docid isn't in the list, position ourselves on the first document after it (or at_end() if no greater docids are present).

If the current position is already the specified docid, this method will leave the position unmodified.

If the specified docid is earlier than the current position, the behaviour is unspecified. A sensible behaviour would be to leave the current position unmodified, but it is also reasonable to move to the specified docid.

The default implementation calls next() repeatedly, which works but skip_to() can often be implemented much more efficiently.

Xapian will always call init() on a PostingSource before calling this for the first time.

Note: in the case of a multi-database search, the docid specified is the docid in the single subdatabase relevant to this posting source. See the init() method for details.

Parameters:

	did	The document id to advance to.
	min_wt	The minimum weight contribution that is needed (this is just a hint which subclasses may ignore).

Reimplemented from Xapian::PostingSource.

Reimplemented in Xapian::DecreasingValueWeightPostingSource.

Definition at line 154 of file postingsource.cc.

References db, Xapian::PostingSource::get_maxweight(), Xapian::ValueIterator::skip_to(), slot, started, value_it, Xapian::Database::valuestream_begin(), and Xapian::Database::valuestream_end().

Referenced by DEFINE_TESTCASE().

Member Data Documentation

Xapian::Database Xapian::ValuePostingSource::db [protected]

The database we're reading values from.

Definition at line 348 of file postingsource.h.

Referenced by at_end(), check(), Xapian::DecreasingValueWeightPostingSource::check(), Xapian::ValueWeightPostingSource::init(), init(), Xapian::DecreasingValueWeightPostingSource::init(), next(), Xapian::DecreasingValueWeightPostingSource::next(), Xapian::DecreasingValueWeightPostingSource::skip_if_in_range(), skip_to(), and Xapian::DecreasingValueWeightPostingSource::skip_to().

Xapian::valueno Xapian::ValuePostingSource::slot [protected]

The slot we're reading values from.

Definition at line 351 of file postingsource.h.

Referenced by at_end(), check(), Xapian::DecreasingValueWeightPostingSource::check(), Xapian::ValueMapPostingSource::clone(), Xapian::ValueWeightPostingSource::clone(), Xapian::DecreasingValueWeightPostingSource::clone(), Xapian::ValueMapPostingSource::get_description(), Xapian::ValueWeightPostingSource::get_description(), Xapian::ValueWeightPostingSource::init(), init(), next(), Xapian::DecreasingValueWeightPostingSource::next(), Xapian::ValueMapPostingSource::serialise(), Xapian::ValueWeightPostingSource::serialise(), Xapian::DecreasingValueWeightPostingSource::serialise(), Xapian::DecreasingValueWeightPostingSource::skip_if_in_range(), skip_to(), and Xapian::DecreasingValueWeightPostingSource::skip_to().

bool Xapian::ValuePostingSource::started [protected]

Flag indicating if we've started (true if we have).

Definition at line 357 of file postingsource.h.

Referenced by at_end(), check(), Xapian::DecreasingValueWeightPostingSource::check(), Xapian::ValueWeightPostingSource::get_weight(), init(), next(), Xapian::DecreasingValueWeightPostingSource::next(), skip_to(), and Xapian::DecreasingValueWeightPostingSource::skip_to().

Xapian::doccount Xapian::ValuePostingSource::termfreq_est [protected]

An estimate of the term frequency.

Subclasses should set this if they are overriding the next(), skip_to() or check() methods.

Definition at line 371 of file postingsource.h.

Referenced by get_termfreq_est(), and init().

Xapian::doccount Xapian::ValuePostingSource::termfreq_max [protected]

An upper bound on the term frequency.

Subclasses should set this if they are overriding the next(), skip_to() or check() methods.

Definition at line 378 of file postingsource.h.

Referenced by get_termfreq_max(), and init().

Xapian::doccount Xapian::ValuePostingSource::termfreq_min [protected]

A lower bound on the term frequency.

Subclasses should set this if they are overriding the next(), skip_to() or check() methods to return fewer documents.

Definition at line 364 of file postingsource.h.

Referenced by get_termfreq_min(), and init().

Xapian::ValueIterator Xapian::ValuePostingSource::value_it [protected]

Value stream iterator.

Definition at line 354 of file postingsource.h.

Referenced by at_end(), check(), Xapian::DecreasingValueWeightPostingSource::check(), get_docid(), Xapian::ValueMapPostingSource::get_weight(), Xapian::ValueWeightPostingSource::get_weight(), next(), Xapian::DecreasingValueWeightPostingSource::next(), Xapian::DecreasingValueWeightPostingSource::skip_if_in_range(), skip_to(), and Xapian::DecreasingValueWeightPostingSource::skip_to().

The documentation for this class was generated from the following files:

include/xapian/postingsource.h
api/postingsource.cc


Public Member Functions
	ValuePostingSource (Xapian::valueno slot_)
	Construct a ValuePostingSource.
Xapian::doccount	get_termfreq_min () const
	A lower bound on the number of documents this object can return.
Xapian::doccount	get_termfreq_est () const
	An estimate of the number of documents this object can return.
Xapian::doccount	get_termfreq_max () const
	An upper bound on the number of documents this object can return.
void	next (Xapian::weight min_wt)
	Advance the current position to the next matching document.
void	skip_to (Xapian::docid min_docid, Xapian::weight min_wt)
	Advance to the specified docid.
bool	check (Xapian::docid min_docid, Xapian::weight min_wt)
	Check if the specified docid occurs.
bool	at_end () const
	Return true if the current position is past the last entry in this list.
Xapian::docid	get_docid () const
	Return the current docid.
void	init (const Database &db_)
	Set this PostingSource to the start of the list of postings.
Protected Attributes
Xapian::Database	db
	The database we're reading values from.
Xapian::valueno	slot
	The slot we're reading values from.
Xapian::ValueIterator	value_it
	Value stream iterator.
bool	started
	Flag indicating if we've started (true if we have).
Xapian::doccount	termfreq_min
	A lower bound on the term frequency.
Xapian::doccount	termfreq_est
	An estimate of the term frequency.
Xapian::doccount	termfreq_max
	An upper bound on the term frequency.