A posting source which returns a fixed weight for all documents. More...

#include <postingsource.h>

Inheritance diagram for Xapian::FixedWeightPostingSource:

Collaboration diagram for Xapian::FixedWeightPostingSource:

Public Member Functions
	FixedWeightPostingSource (double wt)
	Construct a FixedWeightPostingSource. More...

Xapian::doccount	get_termfreq_min () const override
	A lower bound on the number of documents this object can return. More...

Xapian::doccount	get_termfreq_est () const override
	An estimate of the number of documents this object can return. More...

Xapian::doccount	get_termfreq_max () const override
	An upper bound on the number of documents this object can return. More...

double	get_weight () const override
	Return the weight contribution for the current document. More...

void	next (double min_wt) override
	Advance the current position to the next matching document. More...

void	skip_to (Xapian::docid min_docid, double min_wt) override
	Advance to the specified docid. More...

bool	check (Xapian::docid min_docid, double min_wt) override
	Check if the specified docid occurs. More...

bool	at_end () const override
	Return true if the current position is past the last entry in this list. More...

Xapian::docid	get_docid () const override
	Return the current docid. More...

FixedWeightPostingSource *	clone () const override
	Clone the posting source. More...

std::string	name () const override
	Name of the posting source class. More...

std::string	serialise () const override
	Serialise object parameters into a string. More...

FixedWeightPostingSource *	unserialise (const std::string &serialised) const override
	Create object given string serialisation returned by serialise(). More...

void	reset (const Database &db_, Xapian::doccount shard_index) override
	Set this PostingSource to the start of the list of postings. More...

std::string	get_description () const override
	Return a string describing this object. More...

Public Member Functions inherited from Xapian::PostingSource
	PostingSource () noexcept
	Allow subclasses to be instantiated. More...

virtual	~PostingSource ()

void	set_maxweight (double max_weight)
	Specify an upper bound on what get_weight() will return from now on. More...

double	get_maxweight () const noexcept
	Return the currently set upper bound on what get_weight() can return. More...

virtual PostingSource *	unserialise_with_registry (const std::string &serialised, const Registry &registry) const
	Create object given string serialisation returned by serialise(). More...

virtual void	init (const Database &db)
	Older method which did the same job as reset(). More...

PostingSource *	release ()
	Start reference counting this object. More...

const PostingSource *	release () const
	Start reference counting this object. More...

Public Member Functions inherited from Xapian::Internal::opt_intrusive_base
	opt_intrusive_base (const opt_intrusive_base &)

opt_intrusive_base &	operator= (const opt_intrusive_base &)

	opt_intrusive_base ()
	Construct object which is initially not reference counted. More...

virtual	~opt_intrusive_base ()

void	ref () const

void	unref () const

Private Attributes
Xapian::Database	db
	The database we're reading documents from. More...

Xapian::doccount	termfreq
	Number of documents in the posting source. More...

Xapian::PostingIterator	it
	Iterator over all documents. More...

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

Xapian::docid	check_docid
	The docid last passed to check() (0 if check() wasn't the last move). More...

Additional Inherited Members
Public Attributes inherited from Xapian::Internal::opt_intrusive_base
unsigned	_refs
	Reference count. More...

Protected Member Functions inherited from Xapian::Internal::opt_intrusive_base
void	release () const
	Start reference counting. More...

Detailed Description

A posting source which returns a fixed weight for all documents.

This returns entries for all documents in the given database, with a fixed weight (specified by a parameter to the constructor). This can be used to boost a sub-query by OP_AND-ing a FixedWeightPostingSource with that sub-query - this OP_AND will match the same documents as the sub-query does, but documents matching the subquery will get the specified extra weight contribution.

Definition at line 709 of file postingsource.h.

Constructor & Destructor Documentation

◆ FixedWeightPostingSource()

Xapian::FixedWeightPostingSource::FixedWeightPostingSource ( double wt )

explicit

Construct a FixedWeightPostingSource.

Parameters

wt	The fixed weight to return.

Definition at line 407 of file postingsource.cc.

References Xapian::PostingSource::set_maxweight().

Referenced by clone(), and unserialise().

Member Function Documentation

◆ at_end()

bool Xapian::FixedWeightPostingSource::at_end ( ) const

overridevirtual

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 494 of file postingsource.cc.

References check_docid, db, it, Xapian::Database::postlist_end(), and started.

Referenced by DEFINE_TESTCASE().

◆ check()

bool Xapian::FixedWeightPostingSource::check	(	Xapian::docid	did,
		double	min_wt
	)

overridevirtual

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 reset() 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 reset() 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.

Definition at line 485 of file postingsource.cc.

References check_docid.

Referenced by DEFINE_TESTCASE().

◆ clone()

FixedWeightPostingSource * Xapian::FixedWeightPostingSource::clone ( ) const

overridevirtual

Clone the posting source.

The clone should inherit the configuration of the parent, but need not inherit the state. ie, the clone does not need to be in the same iteration position as the original: the matcher will always call reset() on the clone before attempting to move the iterator, or read the information about the current position of the iterator.

This may return NULL to indicate that cloning is not supported. In this case, the PostingSource may only be used with a single-database search.

The default implementation returns NULL.

Note that the returned object will be deallocated by Xapian after use with "delete". If you want to handle the deletion in a special way (for example when wrapping the Xapian API for use from another language) then you can define a static operator delete method in your subclass as shown here: https://trac.xapian.org/ticket/554#comment:1

Reimplemented from Xapian::PostingSource.

Definition at line 508 of file postingsource.cc.

References FixedWeightPostingSource(), and Xapian::PostingSource::get_maxweight().

◆ get_description()

string Xapian::FixedWeightPostingSource::get_description ( ) const

overridevirtual

Return a string describing this object.

This default implementation returns a generic answer. This default it provided to avoid forcing those deriving their own PostingSource subclass from having to implement this (they may not care what get_description() gives for their subclass).

Reimplemented from Xapian::PostingSource.

Definition at line 547 of file postingsource.cc.

References Xapian::PostingSource::get_maxweight(), and Xapian::Internal::str().

Referenced by DEFINE_TESTCASE().

◆ get_docid()

Xapian::docid Xapian::FixedWeightPostingSource::get_docid ( ) const

overridevirtual

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 reset() method for details.

Implements Xapian::PostingSource.

Definition at line 501 of file postingsource.cc.

References check_docid, and it.

Referenced by DEFINE_TESTCASE().

◆ get_termfreq_est()

Xapian::doccount Xapian::FixedWeightPostingSource::get_termfreq_est ( ) const

overridevirtual

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 reset() on a PostingSource before calling this for the first time.

Implements Xapian::PostingSource.

Definition at line 422 of file postingsource.cc.

References termfreq.

◆ get_termfreq_max()

Xapian::doccount Xapian::FixedWeightPostingSource::get_termfreq_max ( ) const

overridevirtual

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

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

Implements Xapian::PostingSource.

Definition at line 428 of file postingsource.cc.

References termfreq.

◆ get_termfreq_min()

Xapian::doccount Xapian::FixedWeightPostingSource::get_termfreq_min ( ) const

overridevirtual

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

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

Implements Xapian::PostingSource.

Definition at line 416 of file postingsource.cc.

References termfreq.

◆ get_weight()

double Xapian::FixedWeightPostingSource::get_weight ( ) const

overridevirtual

Return the weight contribution for the current document.

This default implementation always returns 0, for convenience when implementing "weight-less" PostingSource subclasses.

This method may assume that it will only be called when there is a "current document". In detail: Xapian will always call reset() on a PostingSource before calling this for the first time. It will also only call this if the PostingSource reports that it is pointing to a valid document (ie, it will not call it before calling at least one of next(), skip_to() or check(), and will ensure that the PostingSource is not at the end by calling at_end()).

Reimplemented from Xapian::PostingSource.

Definition at line 434 of file postingsource.cc.

References Xapian::PostingSource::get_maxweight().

◆ name()

string Xapian::FixedWeightPostingSource::name ( ) const

overridevirtual

Name of the posting source class.

This is used when serialising and unserialising posting sources; for example, for performing remote searches.

If the subclass is in a C++ namespace, the namespace should be included in the name, using "::" as a separator. For example, for a PostingSource subclass called "FooPostingSource" in the "Xapian" namespace the result of this call should be "Xapian::FooPostingSource".

This should only be implemented if serialise() and unserialise() are also implemented. The default implementation returns an empty string.

If this returns an empty string, Xapian will assume that serialise() and unserialise() are not implemented.

Reimplemented from Xapian::PostingSource.

Definition at line 514 of file postingsource.cc.

◆ next()

void Xapian::FixedWeightPostingSource::next ( double min_wt )

overridevirtual

Advance the current position to the next matching document.

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

Xapian will always call reset() 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.

Definition at line 440 of file postingsource.cc.

References check_docid, db, Xapian::PostingSource::get_maxweight(), it, Xapian::Database::postlist_begin(), Xapian::Database::postlist_end(), Xapian::PostingIterator::skip_to(), and started.

Referenced by DEFINE_TESTCASE().

◆ reset()

void Xapian::FixedWeightPostingSource::reset	(	const Database &	db,
		Xapian::doccount	shard_index
	)

overridevirtual

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, reset() 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.
shard_index	The 0-based index indicating which shard in a multi-database db is. This can be useful if you have an external source of postings corresponding to each shard.

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.

A default implementation is provided which calls the older init() method to allow existing subclasses to continue to work, but the default implementation of init() throws Xapian::InvalidOperationError so you must override either this method or init(). In new code, override this method in preference.

Since: Added in Xapian 2.0.0.

Reimplemented from Xapian::PostingSource.

Definition at line 538 of file postingsource.cc.

References check_docid, db, Xapian::Database::get_doccount(), started, and termfreq.

Referenced by DEFINE_TESTCASE().

◆ serialise()

string Xapian::FixedWeightPostingSource::serialise ( ) const

overridevirtual

Serialise object parameters into a string.

The serialised parameters should represent the configuration of the posting source, but need not (indeed, should not) represent the current iteration state.

If you don't want to support the remote backend, you can use the default implementation which simply throws Xapian::UnimplementedError.

Reimplemented from Xapian::PostingSource.

Definition at line 520 of file postingsource.cc.

References Xapian::PostingSource::get_maxweight(), and serialise_double().

◆ skip_to()

void Xapian::FixedWeightPostingSource::skip_to	(	Xapian::docid	did,
		double	min_wt
	)

overridevirtual

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 reset() 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 reset() 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.

Definition at line 462 of file postingsource.cc.

References check_docid, db, Xapian::PostingSource::get_maxweight(), it, Xapian::Database::postlist_begin(), Xapian::Database::postlist_end(), Xapian::PostingIterator::skip_to(), and started.

Referenced by DEFINE_TESTCASE().

◆ unserialise()

FixedWeightPostingSource * Xapian::FixedWeightPostingSource::unserialise ( const std::string & serialised ) const

overridevirtual

Create object given string serialisation returned by serialise().

Note that the returned object will be deallocated by Xapian after use with "delete". If you want to handle the deletion in a special way (for example when wrapping the Xapian API for use from another language) then you can define a static operator delete method in your subclass as shown here: https://trac.xapian.org/ticket/554#comment:1

If you don't want to support the remote backend, you can use the default implementation which simply throws Xapian::UnimplementedError.

Parameters

serialised A serialised instance of this PostingSource subclass.

Reimplemented from Xapian::PostingSource.

Definition at line 526 of file postingsource.cc.

References FixedWeightPostingSource(), p, and unserialise_double().

Member Data Documentation

◆ check_docid

Xapian::docid Xapian::FixedWeightPostingSource::check_docid

private

The docid last passed to check() (0 if check() wasn't the last move).

Definition at line 723 of file postingsource.h.

Referenced by at_end(), check(), get_docid(), next(), reset(), and skip_to().

◆ db

Xapian::Database Xapian::FixedWeightPostingSource::db

private

The database we're reading documents from.

Definition at line 711 of file postingsource.h.

Referenced by at_end(), next(), reset(), and skip_to().

◆ it

Xapian::PostingIterator Xapian::FixedWeightPostingSource::it

private

Iterator over all documents.

Definition at line 717 of file postingsource.h.

Referenced by at_end(), get_docid(), next(), and skip_to().

◆ started

bool Xapian::FixedWeightPostingSource::started

private

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

Definition at line 720 of file postingsource.h.

Referenced by at_end(), next(), reset(), and skip_to().

◆ termfreq

Xapian::doccount Xapian::FixedWeightPostingSource::termfreq

private

Number of documents in the posting source.

Definition at line 714 of file postingsource.h.

Referenced by get_termfreq_est(), get_termfreq_max(), get_termfreq_min(), and reset().

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

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

Public Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ FixedWeightPostingSource()

Member Function Documentation

◆ at_end()

◆ check()

◆ clone()

◆ get_description()

◆ get_docid()

◆ get_termfreq_est()

◆ get_termfreq_max()

◆ get_termfreq_min()

◆ get_weight()

◆ name()

◆ next()

◆ reset()

◆ serialise()

◆ skip_to()

◆ unserialise()

Member Data Documentation

◆ check_docid

◆ db

◆ it

◆ started

◆ termfreq