Class representing a query. More...

Public Types
enum	op { OP_AND = 0, OP_OR = 1, OP_AND_NOT = 2, OP_XOR = 3, OP_AND_MAYBE = 4, OP_FILTER = 5, OP_NEAR = 6, OP_PHRASE = 7, OP_VALUE_RANGE = 8, OP_SCALE_WEIGHT = 9, OP_ELITE_SET = 10, OP_VALUE_GE = 11, OP_VALUE_LE = 12, OP_SYNONYM = 13, OP_MAX = 14, OP_WILDCARD = 15, OP_INVALID = 99, LEAF_TERM = 100, LEAF_POSTING_SOURCE, LEAF_MATCH_ALL, LEAF_MATCH_NOTHING }
	Query operators. More...

enum	{ WILDCARD_LIMIT_ERROR, WILDCARD_LIMIT_FIRST, WILDCARD_LIMIT_MOST_FREQUENT }

Public Member Functions
	Query ()
	Default constructor.

	~Query ()
	Destructor.

	Query (const Query &o)
	Copying is allowed. More...

Query &	operator= (const Query &o)
	Copying is allowed. More...

	Query (const std::string &term, Xapian::termcount wqf=1, Xapian::termpos pos=0)
	Construct a Query object for a term. More...

	Query (Xapian::PostingSource *source)
	Construct a Query object for a PostingSource. More...

	Query (double factor, const Xapian::Query &subquery)
	Scale using OP_SCALE_WEIGHT. More...

	Query (op op_, const Xapian::Query &subquery, double factor)
	Scale using OP_SCALE_WEIGHT. More...

	Query (op op_, const Xapian::Query &a, const Xapian::Query &b)
	Construct a Query object by combining two others. More...

	Query (op op_, const std::string &a, const std::string &b)
	Construct a Query object by combining two terms. More...

	Query (op op_, Xapian::valueno slot, const std::string &limit)
	Construct a Query object for a single-ended value range. More...

	Query (op op_, Xapian::valueno slot, const std::string &begin, const std::string &end)
	Construct a Query object for a value range. More...

	Query (op op_, const std::string &pattern, Xapian::termcount max_expansion=0, int max_type=WILDCARD_LIMIT_ERROR, op combiner=OP_SYNONYM)
	Query constructor for OP_WILDCARD queries. More...

template<typename I >
	Query (op op_, I begin, I end, Xapian::termcount window=0)
	Construct a Query object from a begin/end iterator pair. More...

const TermIterator	get_terms_begin () const
	Begin iterator for terms in the query object.

const TermIterator	get_terms_end () const
	End iterator for terms in the query object.

const TermIterator	get_unique_terms_begin () const
	Begin iterator for unique terms in the query object. More...

Xapian::termcount	get_length () const
	Return the length of this query object. More...

bool	empty () const
	Check if this query is Xapian::Query::MatchNothing. More...

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

op	get_type () const
	Get the type of the top level of the query. More...

size_t	get_num_subqueries () const
	Get the number of subqueries of the top level query. More...

const Query	get_subquery (size_t n) const
	Read a top level subquery. More...

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

const Query	operator &= (const Query &o)
	Combine with another Xapian::Query object using OP_AND. More...

const Query	operator\|= (const Query &o)
	Combine with another Xapian::Query object using OP_OR. More...

const Query	operator^= (const Query &o)
	Combine with another Xapian::Query object using OP_XOR. More...

const Query	operator*= (double factor)
	Scale using OP_SCALE_WEIGHT. More...

const Query	operator/= (double factor)
	Inverse scale using OP_SCALE_WEIGHT. More...

	Query (Query::op op_)
	Construct with just an operator. More...

Static Public Member Functions
static const Query	unserialise (const std::string &serialised, const Registry &reg=Registry())
	Unserialise a string and return a Query object. More...

Static Public Attributes
static const Xapian::Query	MatchNothing
	A query matching no documents. More...

static const Xapian::Query	MatchAll
	A query matching all documents. More...

Detailed Description

Class representing a query.

Member Enumeration Documentation

◆ anonymous enum

anonymous enum

Enumerator

WILDCARD_LIMIT_ERROR

Throw an error if OP_WILDCARD exceeds its expansion limit.

Xapian::WildcardError will be thrown when the query is actually run.

WILDCARD_LIMIT_FIRST

Stop expanding when OP_WILDCARD reaches its expansion limit.

This makes the wildcard expand to only the first N terms (sorted by byte order).

WILDCARD_LIMIT_MOST_FREQUENT

Limit OP_WILDCARD expansion to the most frequent terms.

If OP_WILDCARD would expand to more than its expansion limit, the most frequent terms are taken. This approach works well for cases such as expanding a partial term at the end of a query string which the user hasn't finished typing yet - as well as being less expense to evaluate than the full expansion, using only the most frequent terms tends to give better results too.

◆ op

enum Xapian::Query::op

Query operators.

Enumerator

OP_ELITE_SET

Pick the best N subqueries and combine with OP_OR.

If you want to implement a feature which finds documents similar to a piece of text, an obvious approach is to build an "OR" query from all the terms in the text, and run this query against a database containing the documents. However such a query can contain a lots of terms and be quite slow to perform, yet many of these terms don't contribute usefully to the results.

The OP_ELITE_SET operator can be used instead of OP_OR in this situation. OP_ELITE_SET selects the most important ''N'' terms and then acts as an OP_OR query with just these, ignoring any other terms. This will usually return results just as good as the full OP_OR query, but much faster.

In general, the OP_ELITE_SET operator can be used when you have a large OR query, but it doesn't matter if the search completely ignores some of the less important terms in the query.

The subqueries don't have to be terms, but if they aren't then OP_ELITE_SET will look at the estimated frequencies of the subqueries and so could pick a subset which don't actually match any documents even if the full OR would match some.

You can specify a parameter to the query constructor which control the number of terms which OP_ELITE_SET will pick. If not specified, this defaults to 10 (Xapian used to default to ceil(sqrt(number_of_subqueries)) if there are more than 100 subqueries, but this rather arbitrary special case was dropped in 1.3.0). For example, this will pick the best 7 terms:

        Xapian::Query query(Xapian::Query::OP_ELITE_SET, subqs.begin(), subqs.end(), 7);

If the number of subqueries is less than this threshold, OP_ELITE_SET behaves identically to OP_OR.

Constructor & Destructor Documentation

◆ Query() [1/12]

Xapian::Query::Query ( const Query & o )

inline

Copying is allowed.

The internals are reference counted, so copying is cheap.

◆ Query() [2/12]

Xapian::Query::Query	(	const std::string &	term,
		Xapian::termcount	wqf = `1`,
		Xapian::termpos	pos = `0`
	)

Construct a Query object for a term.

◆ Query() [3/12]

Xapian::Query::Query ( Xapian::PostingSource * source )

explicit

Construct a Query object for a PostingSource.

◆ Query() [4/12]

Xapian::Query::Query	(	double	factor,
		const Xapian::Query &	subquery
	)

Scale using OP_SCALE_WEIGHT.

Parameters

factor	Non-negative real number to multiply weights by.
subquery	Query object to scale weights from.

◆ Query() [5/12]

Xapian::Query::Query	(	op	op_,
		const Xapian::Query &	subquery,
		double	factor
	)

Scale using OP_SCALE_WEIGHT.

In this form, the op_ parameter is totally redundant - use Query(factor, subquery) in preference.

Parameters

op_	Must be OP_SCALE_WEIGHT.
factor	Non-negative real number to multiply weights by.
subquery	Query object to scale weights from.

◆ Query() [6/12]

Xapian::Query::Query	(	op	op_,
		const Xapian::Query &	a,
		const Xapian::Query &	b
	)

inline

Construct a Query object by combining two others.

Parameters

op_	The operator to combine the queries with.
a	First subquery.
b	Second subquery.

◆ Query() [7/12]

Xapian::Query::Query	(	op	op_,
		const std::string &	a,
		const std::string &	b
	)

inline

Construct a Query object by combining two terms.

Parameters

op_	The operator to combine the terms with.
a	First term.
b	Second term.

◆ Query() [8/12]

Xapian::Query::Query	(	op	op_,
		Xapian::valueno	slot,
		const std::string &	limit
	)

Construct a Query object for a single-ended value range.

Parameters

op_	Must be OP_VALUE_LE or OP_VALUE_GE currently.
slot	The value slot to work over.
limit	The limit of the range.

◆ Query() [9/12]

Xapian::Query::Query	(	op	op_,
		Xapian::valueno	slot,
		const std::string &	begin,
		const std::string &	end
	)

Construct a Query object for a value range.

Parameters

op_	Must be OP_VALUE_RANGE currently.
slot	The value slot to work over.
begin	Start of the range.
end	End of the range.

◆ Query() [10/12]

Xapian::Query::Query	(	op	op_,
		const std::string &	pattern,
		Xapian::termcount	max_expansion = `0`,
		int	max_type = `WILDCARD_LIMIT_ERROR`,
		op	combiner = `OP_SYNONYM`
	)

Query constructor for OP_WILDCARD queries.

Parameters

op_	Must be OP_WILDCARD
pattern	The wildcard pattern - currently this is just a string and the wildcard expands to terms which start with exactly this string.
max_expansion	The maximum number of terms to expand to (default: 0, which means no limit)
max_type	How to enforce max_expansion - one of WILDCARD_LIMIT_ERROR (the default), WILDCARD_LIMIT_FIRST or WILDCARD_LIMIT_MOST_FREQUENT. When searching multiple databases, the expansion limit is currently applied independently for each database, so the total number of terms may be higher than the limit. This is arguably a bug, and may change in future versions.
combiner	The op_ to combine the terms with - one of OP_SYNONYM (the default), OP_OR or OP_MAX.

◆ Query() [11/12]

template<typename I >

Xapian::Query::Query	(	op	op_,
		I	begin,
		I	end,
		Xapian::termcount	window = `0`
	)

inline

Construct a Query object from a begin/end iterator pair.

Dereferencing the iterator should return a Xapian::Query, a non-NULL Xapian::Query*, a std::string or a type which converts to one of these (e.g. const char*).

Parameters

op_	The operator to combine the queries with.
begin	Begin iterator.
end	End iterator.
window	Window size for OP_NEAR and OP_PHRASE, or 0 to use the number of subqueries as the window size (default: 0).

◆ Query() [12/12]

Xapian::Query::Query ( Query::op op_ )

inlineexplicit

Construct with just an operator.

Parameters

op_	The operator to use - currently only OP_INVALID is useful.

Member Function Documentation

◆ empty()

bool Xapian::Query::empty ( ) const

inline

Check if this query is Xapian::Query::MatchNothing.

◆ get_length()

Xapian::termcount Xapian::Query::get_length ( ) const

Return the length of this query object.

◆ get_num_subqueries()

size_t Xapian::Query::get_num_subqueries ( ) const

Get the number of subqueries of the top level query.

◆ get_subquery()

const Query Xapian::Query::get_subquery ( size_t n ) const

Read a top level subquery.

Parameters

n	Return the n-th subquery (starting from 0) - only valid when 0 <= n < get_num_subqueries().

◆ get_type()

op Xapian::Query::get_type ( ) const

Get the type of the top level of the query.

◆ get_unique_terms_begin()

const TermIterator Xapian::Query::get_unique_terms_begin ( ) const

Begin iterator for unique terms in the query object.

Terms are sorted and terms with the same name removed from the list.

◆ operator &=()

const Query Xapian::Query::operator&= ( const Query & o )

inline

Combine with another Xapian::Query object using OP_AND.

◆ operator*=()

const Query Xapian::Query::operator*= ( double factor )

inline

Scale using OP_SCALE_WEIGHT.

Parameters

factor Non-negative real number to multiply weights by.

◆ operator/=()

const Query Xapian::Query::operator/= ( double factor )

inline

Inverse scale using OP_SCALE_WEIGHT.

Parameters

factor Positive real number to divide weights by.

◆ operator=()

Query& Xapian::Query::operator= ( const Query & o )

inline

Copying is allowed.

The internals are reference counted, so assignment is cheap.

◆ operator^=()

const Query Xapian::Query::operator^= ( const Query & o )

inline

Combine with another Xapian::Query object using OP_XOR.

◆ operator|=()

const Query Xapian::Query::operator|= ( const Query & o )

inline

Combine with another Xapian::Query object using OP_OR.

◆ serialise()

std::string Xapian::Query::serialise ( ) const

Serialise this object into a string.

◆ unserialise()

static const Query Xapian::Query::unserialise	(	const std::string &	serialised,
		const Registry &	reg = `Registry()`
	)

static

Unserialise a string and return a Query object.

Parameters

serialised	the string to unserialise.
reg	Xapian::Registry object to use to unserialise user-subclasses of Xapian::PostingSource (default: standard registry).

Member Data Documentation

◆ MatchAll

const Xapian::Query Xapian::Query::MatchAll

static

A query matching all documents.

Exactly equivalent to Xapian::Query(std::string()).

Referenced by Xapian::operator/().

◆ MatchNothing

const Xapian::Query Xapian::Query::MatchNothing

static

A query matching no documents.

Exactly equivalent to Xapian::Query().

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

xapian/query.h

Public Types

Public Member Functions

Static Public Member Functions

Static Public Attributes

Detailed Description

Member Enumeration Documentation

◆ anonymous enum

◆ op

Constructor & Destructor Documentation

◆ Query() [1/12]

◆ Query() [2/12]

◆ Query() [3/12]

◆ Query() [4/12]

◆ Query() [5/12]

◆ Query() [6/12]

◆ Query() [7/12]

◆ Query() [8/12]

◆ Query() [9/12]

◆ Query() [10/12]

◆ Query() [11/12]

◆ Query() [12/12]

Member Function Documentation

◆ empty()

◆ get_length()

◆ get_num_subqueries()

◆ get_subquery()

◆ get_type()

◆ get_unique_terms_begin()

◆ operator &=()

◆ operator*=()

◆ operator/=()

◆ operator=()

◆ operator^=()

◆ operator|=()

◆ serialise()

◆ unserialise()

Member Data Documentation

◆ MatchAll

◆ MatchNothing