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

#include <postingsource.h>

Inheritance diagram for Xapian::ValuePostingSource:

Public Member Functions
	ValuePostingSource (Xapian::valueno slot_) noexcept
	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 (double min_wt)
	Advance the current position to the next matching document.
void	skip_to (Xapian::docid min_docid, double min_wt)
	Advance to the specified docid.
bool	check (Xapian::docid min_docid, double 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	reset (const Database &db_, Xapian::doccount shard_index)
	Set this PostingSource to the start of the list of postings.
Xapian::Database	get_database () const
	The database we're reading values from.
Xapian::valueno	get_slot () const
	The slot we're reading values from.
std::string	get_value () const
	Read current value.
void	done ()
	End the iteration.
bool	get_started () const
	Flag indicating if we've started (true if we have).
void	set_termfreq_min (Xapian::doccount termfreq_min_)
	Set a lower bound on the term frequency.
void	set_termfreq_est (Xapian::doccount termfreq_est_)
	An estimate of the term frequency.
void	set_termfreq_max (Xapian::doccount termfreq_max_)
	An upper bound on the term frequency.
std::string	get_description () const
	Return a string describing this object.
Public Member Functions inherited from Xapian::PostingSource
	PostingSource () noexcept
	Allow subclasses to be instantiated.
void	set_maxweight (double max_weight)
	Specify an upper bound on what get_weight() will return from now on.
double	get_maxweight () const noexcept
	Return the currently set upper bound on what get_weight() can return.
virtual double	get_weight () const
	Return the weight contribution for the current document.
virtual PostingSource *	clone () const
	Clone the posting source.
virtual std::string	name () const
	Name of the posting source class.
virtual std::string	serialise () const
	Serialise object parameters into a string.
virtual PostingSource *	unserialise (const std::string &serialised) const
	Create object given string serialisation returned by serialise().
virtual PostingSource *	unserialise_with_registry (const std::string &serialised, const Registry &registry) const
	Create object given string serialisation returned by serialise().
virtual void	init (const Database &db)
	Older method which did the same job as reset().
PostingSource *	release ()
	Start reference counting this object.
const PostingSource *	release () const
	Start reference counting this object.

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.

Constructor & Destructor Documentation

◆ ValuePostingSource()

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

inlineexplicitnoexcept

Construct a ValuePostingSource.

Parameters

slot_ The value slot to read values from.

Member Function Documentation

◆ at_end()

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.

◆ check()

bool Xapian::ValuePostingSource::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 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.

◆ done()

void Xapian::ValuePostingSource::done ( )

inline

End the iteration.

Calls to at_end() will return true after calling this method.

Since: Added in 1.2.23 and 1.3.5.

◆ get_database()

Xapian::Database Xapian::ValuePostingSource::get_database ( ) const

inline

The database we're reading values from.

Since: Added in 1.2.23 and 1.3.5.

◆ get_description()

std::string Xapian::ValuePostingSource::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 from Xapian::PostingSource.

Reimplemented in Xapian::ValueWeightPostingSource.

◆ get_docid()

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 reset() method for details.

Implements Xapian::PostingSource.

◆ get_slot()

Xapian::valueno Xapian::ValuePostingSource::get_slot ( ) const

inline

The slot we're reading values from.

Since: Added in 1.2.23 and 1.3.5.

◆ get_started()

bool Xapian::ValuePostingSource::get_started ( ) const

inline

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

Since: Added in 1.2.23 and 1.3.5.

◆ get_termfreq_est()

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

Implements Xapian::PostingSource.

◆ get_termfreq_max()

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

Implements Xapian::PostingSource.

◆ get_termfreq_min()

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

Implements Xapian::PostingSource.

◆ get_value()

std::string Xapian::ValuePostingSource::get_value ( ) const

inline

Read current value.

Since: Added in 1.2.23 and 1.3.5.

◆ next()

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

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 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.

◆ reset()

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

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, 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.

Reimplemented in Xapian::ValueWeightPostingSource.

◆ set_termfreq_est()

void Xapian::ValuePostingSource::set_termfreq_est ( Xapian::doccount termfreq_est_ )

inline

An estimate of the term frequency.

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

Since: Added in 1.2.23 and 1.3.5.

◆ set_termfreq_max()

void Xapian::ValuePostingSource::set_termfreq_max ( Xapian::doccount termfreq_max_ )

inline

An upper bound on the term frequency.

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

Since: Added in 1.2.23 and 1.3.5.

◆ set_termfreq_min()

void Xapian::ValuePostingSource::set_termfreq_min ( Xapian::doccount termfreq_min_ )

inline

Set 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.

Since: Added in 1.2.23 and 1.3.5.

◆ skip_to()

void Xapian::ValuePostingSource::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 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.

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

xapian/postingsource.h

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

◆ ValuePostingSource()

Member Function Documentation

◆ at_end()

◆ check()

◆ done()

◆ get_database()

◆ get_description()

◆ get_docid()

◆ get_slot()

◆ get_started()

◆ get_termfreq_est()

◆ get_termfreq_max()

◆ get_termfreq_min()

◆ get_value()

◆ next()

◆ reset()

◆ set_termfreq_est()

◆ set_termfreq_max()

◆ set_termfreq_min()

◆ skip_to()