xapian-core  1.5.0
Public Member Functions | List of all members
Xapian::ValuePostingSource Class Reference

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

+ Inheritance diagram for Xapian::ValuePostingSource:

Public Member Functions

 ValuePostingSource (Xapian::valueno slot_) noexcept
 Construct a ValuePostingSource. More...
 
Xapian::doccount get_termfreq_min () const
 A lower bound on the number of documents this object can return. More...
 
Xapian::doccount get_termfreq_est () const
 An estimate of the number of documents this object can return. More...
 
Xapian::doccount get_termfreq_max () const
 An upper bound on the number of documents this object can return. More...
 
void next (double min_wt)
 Advance the current position to the next matching document. More...
 
void skip_to (Xapian::docid min_docid, double min_wt)
 Advance to the specified docid. More...
 
bool check (Xapian::docid min_docid, double min_wt)
 Check if the specified docid occurs. More...
 
bool at_end () const
 Return true if the current position is past the last entry in this list. More...
 
Xapian::docid get_docid () const
 Return the current docid. More...
 
void init (const Database &db_)
 Older method which did the same job as reset(). More...
 
Xapian::Database get_database () const
 The database we're reading values from. More...
 
Xapian::valueno get_slot () const
 The slot we're reading values from. More...
 
std::string get_value () const
 Read current value. More...
 
void done ()
 End the iteration. More...
 
bool get_started () const
 Flag indicating if we've started (true if we have). More...
 
void set_termfreq_min (Xapian::doccount termfreq_min_)
 Set a lower bound on the term frequency. More...
 
void set_termfreq_est (Xapian::doccount termfreq_est_)
 An estimate of the term frequency. More...
 
void set_termfreq_max (Xapian::doccount termfreq_max_)
 An upper bound on the term frequency. More...
 
std::string get_description () const
 Return a string describing this object. More...
 
- 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. More...
 
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. More...
 
virtual PostingSourceclone () 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 PostingSourceunserialise (const std::string &serialised) const
 Create object given string serialisation returned by serialise(). More...
 
virtual PostingSourceunserialise_with_registry (const std::string &serialised, const Registry &registry) const
 Create object given string serialisation returned by serialise(). More...
 
virtual void reset (const Database &db, Xapian::doccount shard_index)
 Set this PostingSource to the start of the list of postings. More...
 
PostingSourcerelease ()
 Start reference counting this object. More...
 
const PostingSourcerelease () const
 Start reference counting this object. More...
 

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

Reimplemented from Xapian::PostingSource.

Reimplemented in Xapian::DecreasingValueWeightPostingSource.

◆ 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::ValueMapPostingSource, Xapian::DecreasingValueWeightPostingSource, and 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.

◆ init()

void Xapian::ValuePostingSource::init ( const Database db)
virtual

Older method which did the same job as reset().

Prior to 1.5.0, instead of reset() there was a method called init() taking one parameter. The default implementation of reset() calls init() to allow existing subclasses to continue to work.

A default implementation of init() is provided so that new subclasses can just override reset() (the default implementation should not actually get called, and will throw Xapian::InvalidOperationError if it is).

Reimplemented from Xapian::PostingSource.

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

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

Implements Xapian::PostingSource.

Reimplemented in Xapian::DecreasingValueWeightPostingSource.

◆ 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
didThe document id to advance to.
min_wtThe minimum weight contribution that is needed (this is just a hint which subclasses may ignore).

Reimplemented from Xapian::PostingSource.

Reimplemented in Xapian::DecreasingValueWeightPostingSource.


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