Base class which provides an "external" source of postings. More...

#include <postingsource.h>

Inheritance diagram for Xapian::PostingSource:

Collaboration diagram for Xapian::PostingSource:

Public Member Functions
	PostingSource ()
	Allow subclasses to be instantiated. More...

virtual	~PostingSource ()

virtual Xapian::doccount	get_termfreq_min () const =0
	A lower bound on the number of documents this object can return. More...

virtual Xapian::doccount	get_termfreq_est () const =0
	An estimate of the number of documents this object can return. More...

virtual Xapian::doccount	get_termfreq_max () const =0
	An upper bound on the number of documents this object can return. More...

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

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

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

virtual Xapian::docid	get_docid () const =0
	Return the current docid. More...

virtual void	next (double min_wt)=0
	Advance the current position to the next matching document. More...

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

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

virtual bool	at_end () const =0
	Return true if the current position is past the last entry in this list. More...

virtual PostingSource *	clone () const
	Clone the posting source. More...

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

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

virtual PostingSource *	unserialise (const std::string &serialised) const
	Create object given string serialisation returned by serialise(). 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)=0
	Set this PostingSource to the start of the list of postings. More...

virtual std::string	get_description () const
	Return a string describing this object. 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 Member Functions
void	operator= (const PostingSource &)
	Don't allow assignment. More...

	PostingSource (const PostingSource &)
	Don't allow copying. More...

void	register_matcher_ (void *matcher)

Private Attributes
double	max_weight_
	The current upper bound on what get_weight() can return. More...

void *	matcher_
	The object to inform of maxweight changes. 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

Base class which provides an "external" source of postings.

Definition at line 47 of file postingsource.h.

Constructor & Destructor Documentation

◆ PostingSource() [1/2]

Xapian::PostingSource::PostingSource ( const PostingSource & )

private

Don't allow copying.

◆ PostingSource() [2/2]

Xapian::PostingSource::PostingSource ( )

inline

Allow subclasses to be instantiated.

Definition at line 67 of file postingsource.h.

◆ ~PostingSource()

Xapian::PostingSource::~PostingSource ( )

virtual

Definition at line 50 of file postingsource.cc.

Member Function Documentation

◆ at_end()

virtual bool Xapian::PostingSource::at_end ( ) const

pure 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.

Implemented in EstimatePS, OnlyTheFirstPostingSource, Xapian::FixedWeightPostingSource, CloneTestPostingSource, Xapian::ValuePostingSource, ChangeMaxweightPostingSource, ExceptionalPostingSource, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, MyPostingSource, and MyOddPostingSource.

Referenced by ExternalPostList::check(), and ExternalPostList::update_after_advance().

◆ check()

bool Xapian::PostingSource::check	(	Xapian::docid	did,
		double	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 in Xapian::FixedWeightPostingSource, Xapian::DecreasingValueWeightPostingSource, Xapian::LatLongDistancePostingSource, and Xapian::ValuePostingSource.

Definition at line 77 of file postingsource.cc.

Referenced by ExternalPostList::check().

◆ clone()

PostingSource * Xapian::PostingSource::clone ( ) const

virtual

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 init() 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 in EstimatePS, Xapian::FixedWeightPostingSource, OnlyTheFirstPostingSource, Xapian::ValueMapPostingSource, CloneTestPostingSource, Xapian::DecreasingValueWeightPostingSource, CheckBoundsPostingSource, SlowDecreasingValueWeightPostingSource, Xapian::ValueWeightPostingSource, Xapian::LatLongDistancePostingSource, ExceptionalPostingSource, MyPostingSource2, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, MyPostingSource, and MyOddPostingSource.

Definition at line 84 of file postingsource.cc.

Referenced by ExternalPostList::ExternalPostList().

◆ get_description()

string Xapian::PostingSource::get_description ( ) const

virtual

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 in EstimatePS, OnlyTheFirstPostingSource, Xapian::FixedWeightPostingSource, Xapian::ValueMapPostingSource, CloneTestPostingSource, Xapian::DecreasingValueWeightPostingSource, Xapian::ValueWeightPostingSource, Xapian::LatLongDistancePostingSource, ChangeMaxweightPostingSource, MyDontAskWeightPostingSource, MyPostingSource2, MyOddWeightingPostingSource, MyPostingSource, and MyOddPostingSource.

Definition at line 115 of file postingsource.cc.

Referenced by ExternalPostList::get_description().

◆ get_docid()

virtual Xapian::docid Xapian::PostingSource::get_docid ( ) const

pure 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.

Implemented in EstimatePS, OnlyTheFirstPostingSource, Xapian::FixedWeightPostingSource, CloneTestPostingSource, Xapian::ValuePostingSource, ChangeMaxweightPostingSource, ExceptionalPostingSource, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, MyPostingSource, and MyOddPostingSource.

Referenced by ExternalPostList::check(), and ExternalPostList::update_after_advance().

◆ get_maxweight()

double Xapian::PostingSource::get_maxweight ( ) const

inline

Return the currently set upper bound on what get_weight() can return.

Definition at line 131 of file postingsource.h.

References name.

Referenced by Xapian::ValuePostingSource::check(), Xapian::DecreasingValueWeightPostingSource::check(), Xapian::FixedWeightPostingSource::clone(), DEFINE_TESTCASE(), Xapian::FixedWeightPostingSource::get_description(), ExternalPostList::get_maxweight(), Xapian::FixedWeightPostingSource::get_weight(), Xapian::ValuePostingSource::next(), Xapian::DecreasingValueWeightPostingSource::next(), Xapian::FixedWeightPostingSource::next(), Xapian::FixedWeightPostingSource::serialise(), Xapian::ValuePostingSource::skip_to(), Xapian::DecreasingValueWeightPostingSource::skip_to(), and Xapian::FixedWeightPostingSource::skip_to().

◆ get_termfreq_est()

virtual Xapian::doccount Xapian::PostingSource::get_termfreq_est ( ) const

pure 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.

Implemented in EstimatePS, OnlyTheFirstPostingSource, Xapian::FixedWeightPostingSource, CloneTestPostingSource, Xapian::ValuePostingSource, ChangeMaxweightPostingSource, ExceptionalPostingSource, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, MyPostingSource, and MyOddPostingSource.

Referenced by ExternalPostList::get_termfreq_est().

◆ get_termfreq_max()

virtual Xapian::doccount Xapian::PostingSource::get_termfreq_max ( ) const

pure 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.

Implemented in EstimatePS, OnlyTheFirstPostingSource, Xapian::FixedWeightPostingSource, CloneTestPostingSource, Xapian::ValuePostingSource, ChangeMaxweightPostingSource, ExceptionalPostingSource, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, MyPostingSource, and MyOddPostingSource.

Referenced by ExternalPostList::get_termfreq_max().

◆ get_termfreq_min()

virtual Xapian::doccount Xapian::PostingSource::get_termfreq_min ( ) const

pure 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.

Implemented in EstimatePS, OnlyTheFirstPostingSource, Xapian::FixedWeightPostingSource, CloneTestPostingSource, Xapian::ValuePostingSource, ChangeMaxweightPostingSource, ExceptionalPostingSource, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, MyPostingSource, and MyOddPostingSource.

Referenced by ExternalPostList::get_termfreq_min().

◆ get_weight()

double Xapian::PostingSource::get_weight ( ) const

virtual

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 init() 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 in Xapian::FixedWeightPostingSource, Xapian::ValueMapPostingSource, Xapian::DecreasingValueWeightPostingSource, Xapian::ValueWeightPostingSource, Xapian::LatLongDistancePostingSource, ChangeMaxweightPostingSource, MyPostingSource2, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, and MyPostingSource.

Definition at line 63 of file postingsource.cc.

Referenced by ExternalPostList::get_weight().

◆ init()

virtual void Xapian::PostingSource::init ( const Database & db )

pure 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: 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.

Implemented in EstimatePS, Xapian::FixedWeightPostingSource, OnlyTheFirstPostingSource, Xapian::ValueMapPostingSource, CloneTestPostingSource, Xapian::DecreasingValueWeightPostingSource, CheckBoundsPostingSource, Xapian::ValueWeightPostingSource, Xapian::LatLongDistancePostingSource, Xapian::ValuePostingSource, ChangeMaxweightPostingSource, ExceptionalPostingSource, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, MyPostingSource, and MyOddPostingSource.

Referenced by ExternalPostList::ExternalPostList().

◆ name()

string Xapian::PostingSource::name ( ) const

virtual

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 in Xapian::FixedWeightPostingSource, Xapian::ValueMapPostingSource, Xapian::DecreasingValueWeightPostingSource, Xapian::ValueWeightPostingSource, Xapian::LatLongDistancePostingSource, ExceptionalPostingSource, and MyPostingSource2.

Definition at line 90 of file postingsource.cc.

Referenced by Xapian::Registry::Internal::add_defaults(), DEFINE_TESTCASE(), and Xapian::Registry::register_posting_source().

◆ next()

virtual void Xapian::PostingSource::next ( double min_wt )

pure virtual

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 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).

Implemented in EstimatePS, OnlyTheFirstPostingSource, Xapian::FixedWeightPostingSource, CloneTestPostingSource, Xapian::DecreasingValueWeightPostingSource, SlowDecreasingValueWeightPostingSource, Xapian::LatLongDistancePostingSource, Xapian::ValuePostingSource, ChangeMaxweightPostingSource, ExceptionalPostingSource, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, MyPostingSource, and MyOddPostingSource.

Referenced by ExternalPostList::next().

◆ operator=()

void Xapian::PostingSource::operator= ( const PostingSource & )

private

Don't allow assignment.

◆ register_matcher_()

void Xapian::PostingSource::register_matcher_ ( void * matcher )

inlineprivate

Set the object to inform of maxweight changes.

This method is for internal use only - it would be private except that would force us to forward declare an internal class in an external API header just to make it a friend.

Definition at line 76 of file postingsource.h.

Referenced by ExternalPostList::ExternalPostList().

◆ release() [1/2]

PostingSource* Xapian::PostingSource::release ( )

inline

Start reference counting this object.

You can transfer ownership of a dynamically allocated PostingSource object to Xapian by calling release() and then passing the object to a Xapian method. Xapian will arrange to delete the object once it is no longer required.

Definition at line 372 of file postingsource.h.

Referenced by DEFINE_TESTCASE(), ExternalPostList::ExternalPostList(), Xapian::Internal::QueryPostingSource::QueryPostingSource(), and Xapian::Query::Internal::unserialise().

◆ release() [2/2]

const PostingSource* Xapian::PostingSource::release ( ) const

inline

Start reference counting this object.

You can transfer ownership of a dynamically allocated PostingSource object to Xapian by calling release() and then passing the object to a Xapian method. Xapian will arrange to delete the object once it is no longer required.

Definition at line 384 of file postingsource.h.

◆ serialise()

string Xapian::PostingSource::serialise ( ) const

virtual

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 in Xapian::FixedWeightPostingSource, Xapian::ValueMapPostingSource, Xapian::DecreasingValueWeightPostingSource, Xapian::ValueWeightPostingSource, Xapian::LatLongDistancePostingSource, and MyPostingSource2.

Definition at line 96 of file postingsource.cc.

Referenced by DEFINE_TESTCASE().

◆ set_maxweight()

void Xapian::PostingSource::set_maxweight ( double max_weight )

Specify an upper bound on what get_weight() will return from now on.

This upper bound is used by the matcher to perform various optimisations, so if you can return a good bound, then matches will generally run faster.

This method should be called after calling init(), and may be called during iteration if the upper bound drops. It is probably only useful to call from subclasses (it was actually a "protected" method prior to Xapian 1.3.4, but that makes it tricky to wrap for other languages).

It is valid for the posting source to have returned a higher value from get_weight() earlier in the iteration, but the posting source must not return a higher value from get_weight() than the currently set upper bound, and the upper bound must not be increased (until init() has been called).

If you don't call this method, the upper bound will default to 0, for convenience when implementing "weight-less" PostingSource subclasses.

Parameters

max_weight The upper bound to set.

Definition at line 53 of file postingsource.cc.

References MultiMatch::recalc_maxweight(), and usual.

Referenced by Xapian::FixedWeightPostingSource::FixedWeightPostingSource(), Xapian::ValuePostingSource::init(), Xapian::ValueWeightPostingSource::init(), Xapian::ValueMapPostingSource::init(), Xapian::LatLongDistancePostingSource::LatLongDistancePostingSource(), and Xapian::DecreasingValueWeightPostingSource::skip_if_in_range().

◆ skip_to()

void Xapian::PostingSource::skip_to	(	Xapian::docid	did,
		double	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 in EstimatePS, OnlyTheFirstPostingSource, Xapian::FixedWeightPostingSource, CloneTestPostingSource, Xapian::DecreasingValueWeightPostingSource, Xapian::LatLongDistancePostingSource, Xapian::ValuePostingSource, ChangeMaxweightPostingSource, ExceptionalPostingSource, MyDontAskWeightPostingSource, MyOddWeightingPostingSource, and MyOddPostingSource.

Definition at line 69 of file postingsource.cc.

Referenced by ExternalPostList::skip_to().

◆ unserialise()

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

virtual

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 in Xapian::FixedWeightPostingSource, Xapian::ValueMapPostingSource, Xapian::DecreasingValueWeightPostingSource, Xapian::ValueWeightPostingSource, and MyPostingSource2.

Definition at line 102 of file postingsource.cc.

Referenced by DEFINE_TESTCASE().

◆ unserialise_with_registry()

PostingSource * Xapian::PostingSource::unserialise_with_registry	(	const std::string &	serialised,
		const Registry &	registry
	)		const

virtual

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

This method is supplied with a Registry object, which can be used when unserialising objects contained within the posting source. The default implementation simply calls unserialise() which doesn't take the Registry object, so you do not need to implement this method unless you want to take advantage of the Registry object when unserialising.

Parameters

serialised	A serialised instance of this PostingSource subclass.
registry	The Xapian::Registry object to use.

Reimplemented in Xapian::LatLongDistancePostingSource.

Definition at line 108 of file postingsource.cc.

Referenced by Xapian::Query::Internal::unserialise().

Member Data Documentation

◆ matcher_

void* Xapian::PostingSource::matcher_

private

The object to inform of maxweight changes.

We store this as a (void*) to avoid needing to declare an internal type in an external header. It's actually (MultiMatch *).

Definition at line 63 of file postingsource.h.

◆ max_weight_

double Xapian::PostingSource::max_weight_

private

The current upper bound on what get_weight() can return.

Definition at line 56 of file postingsource.h.

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

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

Public Member Functions

Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ PostingSource() [1/2]

◆ PostingSource() [2/2]

◆ ~PostingSource()

Member Function Documentation

◆ at_end()

◆ check()

◆ clone()

◆ get_description()

◆ get_docid()

◆ get_maxweight()

◆ get_termfreq_est()

◆ get_termfreq_max()

◆ get_termfreq_min()

◆ get_weight()

◆ init()

◆ name()

◆ next()

◆ operator=()

◆ register_matcher_()

◆ release() [1/2]

◆ release() [2/2]

◆ serialise()

◆ set_maxweight()

◆ skip_to()

◆ unserialise()

◆ unserialise_with_registry()

Member Data Documentation

◆ matcher_

◆ max_weight_