# Xapian::QueryParser Class Reference

Build a Xapian::Query object from a user query string. More...

List of all members.

## Public Types

enum | feature_flag { FLAG_BOOLEAN = 1, FLAG_PHRASE = 2, FLAG_LOVEHATE = 4, FLAG_BOOLEAN_ANY_CASE = 8, FLAG_WILDCARD = 16, FLAG_PURE_NOT = 32, FLAG_PARTIAL = 64, FLAG_SPELLING_CORRECTION = 128, FLAG_SYNONYM = 256, FLAG_AUTO_SYNONYMS = 512, FLAG_AUTO_MULTIWORD_SYNONYMS = 1024 | FLAG_AUTO_SYNONYMS, FLAG_DEFAULT = FLAG_PHRASE|FLAG_BOOLEAN|FLAG_LOVEHATE }
| Enum of feature flags. More...

## Public Member Functions

| QueryParser (const QueryParser &o)
| Copy constructor.
QueryParser & | operator= (const QueryParser &o)
| Assignment.
| QueryParser ()
| Default constructor.
| ~QueryParser ()
| Destructor.
void | set_stemmer (const Xapian::Stem &stemmer)
| Set the stemmer.
void | set_stemming_strategy (stem_strategy strategy)
| Set the stemming strategy.
void | set_stopper (const Stopper *stop=NULL)
| Set the stopper.
void | set_default_op (Query::op default_op)
| Set the default operator.
Query::op | get_default_op () const
| Get the current default operator.
void | set_database (const Database &db)
| Specify the database being searched.
Query | parse_query (const std::string &query_string, unsigned flags=FLAG_DEFAULT, const std::string &default_prefix=std::string())
| Parse a query.
void | add_prefix (const std::string &field, const std::string &prefix)
| Add a probabilistic term prefix.
void | add_boolean_prefix (const std::string &field, const std::string &prefix)
| Add a boolean term prefix allowing the user to restrict a search with a boolean filter specified in the free text query.
TermIterator | stoplist_begin () const
| Iterate over terms omitted from the query as stopwords.
TermIterator | unstem_begin (const std::string &term) const
| Iterate over unstemmed forms of the given (stemmed) term used in the query.
void | add_valuerangeprocessor (Xapian::ValueRangeProcessor *vrproc)
| Register a ValueRangeProcessor.
std::string | get_corrected_query_string () const
| Get the spelling-corrected query string.
std::string | get_description () const
| Return a string describing this object.

## Detailed Description

Build a Xapian::Query object from a user query string.

## Member Enumeration Documentation

enum Xapian::QueryParser::feature_flag

Enum of feature flags.

Enumerator:

  FLAG_BOOLEAN | Support AND, OR, etc and bracketed subexpressions.
  FLAG_PHRASE | Support quoted phrases.
  FLAG_LOVEHATE | Support + and -.
  FLAG_BOOLEAN_ANY_CASE | Support AND, OR, etc even if they aren't in ALLCAPS.
  FLAG_WILDCARD | Support right truncation (e.g. Xap*). NB: You need to tell the QueryParser object which database to expand wildcards from by calling set_database.
  FLAG_PURE_NOT | Allow queries such as 'NOT apples'. These require the use of a list of all documents in the database which is potentially expensive, so this feature isn't enabled by default.
  FLAG_PARTIAL | Enable partial matching. Partial matching causes the parser to treat the query as a "partially entered" search. This will automatically treat the final word as a wildcarded match, unless it is followed by whitespace, to produce more stable results from interactive searches. NB: You need to tell the QueryParser object which database to expand wildcards from by calling set_database.

  FLAG_SPELLING_CORRECTION

  Enable spelling correction.

  For each word in the query which doesn't exist as a term in the database, Database::get_spelling_suggestion() will be called and if a suggestion is returned, a corrected version of the query string will be built up which can be read using QueryParser::get_corrected_query_string(). The query returned is based on the uncorrected query string however - if you want a parsed query based on the corrected query string, you must call QueryParser::parse_query() again.

  NB: You must also call set_database() for this to work.

  FLAG_SYNONYM | Enable synonym operator '~'. NB: You must also call set_database() for this to work.
  FLAG_AUTO_SYNONYMS | Enable automatic use of synonyms for single terms. NB: You must also call set_database() for this to work.
  FLAG_AUTO_MULTIWORD_SYNONYMS | Enable automatic use of synonyms for single terms and groups of terms. NB: You must also call set_database() for this to work.
  FLAG_DEFAULT | The default flags. Used if you don't explicitly pass any to parse_query(). Added in Xapian 1.0.11.

## Member Function Documentation

void Xapian::QueryParser::add_boolean_prefix | ( | const std::string & | field,
|  | const std::string & | prefix |
| ) |  |  |

Add a boolean term prefix allowing the user to restrict a search with a boolean filter specified in the free text query.

For example:

      qp.add_boolean_prefix("site", "H");

This allows the user to restrict a search with site:xapian.org which will be converted to Hxapian.org combined with any probabilistic query with `Xapian::Query::OP_FILTER`.

If multiple boolean filters are specified in a query for the same prefix, they will be combined with the `Xapian::Query::OP_OR` operator. Then, if there are boolean filters for different prefixes, they will be combined with the `Xapian::Query::OP_AND` operator.

Multiple fields can be mapped to the same prefix (so for example you can make site: and domain: aliases for each other). Instances of fields with different aliases but the same prefix will still be combined with the OR operator.

For example, if "site" and "domain" map to "H", but author maps to "A", a search for "site:foo domain:bar author:Fred" will map to "(Hfoo OR Hbar) AND Afred".

As of 1.0.4, you can call this method multiple times with the same value of field to allow a single field to be mapped to multiple prefixes. Multiple terms being generated for such a field, and combined with `Xapian::Query::OP_OR`.

Calling this method with an empty string for field will cause a `Xapian::InvalidArgumentError`.

If you call `add_prefix()` and `add_boolean_prefix()` for the same value of field, a `Xapian::InvalidOperationError` exception will be thrown.

In 1.0.3 and earlier, subsequent calls to this method with the same value of field had no effect.

Parameters:

  | field | The user visible field name
  | prefix | The term prefix to map this to

void Xapian::QueryParser::add_prefix | ( | const std::string & | field,
|  | const std::string & | prefix |
| ) |  |  |

Add a probabilistic term prefix.

For example:

      qp.add_prefix("author", "A");

This allows the user to search for author:Orwell which will be converted to a search for the term "Aorwell".

Multiple fields can be mapped to the same prefix. For example, you can make title: and subject: aliases for each other.

As of 1.0.4, you can call this method multiple times with the same value of field to allow a single field to be mapped to multiple prefixes. Multiple terms being generated for such a field, and combined with `Xapian::Query::OP_OR`.

If any prefixes are specified for the empty field name (i.e. you call this method with an empty string as the first parameter) these prefixes will be used for terms without a field specifier. If you do this and also specify the `default_prefix` parameter to `parse_query()`, then the `default_prefix` parameter will override.

If the prefix parameter is empty, then "field:word" will produce the term "word" (and this can be one of several prefixes for a particular field, or for terms without a field specifier).

If you call `add_prefix()` and `add_boolean_prefix()` for the same value of field, a `Xapian::InvalidOperationError` exception will be thrown.

In 1.0.3 and earlier, subsequent calls to this method with the same value of field had no effect.

Parameters:

  | field | The user visible field name
  | prefix | The term prefix to map this to

std::string Xapian::QueryParser::get_corrected_query_string | ( |  | ) | const

Get the spelling-corrected query string.

This will only be set if FLAG_SPELLING_CORRECTION is specified when QueryParser::parse_query() was last called.

If there were no corrections, an empty string is returned.

Query::op Xapian::QueryParser::get_default_op | ( |  | ) | const

Get the current default operator.

Query Xapian::QueryParser::parse_query | ( | const std::string & | query_string,
|  | unsigned | flags = `FLAG_DEFAULT`,
|  | const std::string & | default_prefix = `std::string()` |
| ) |  |  |

Parse a query.

Parameters:

  | query_string | A free-text query as entered by a user
  | flags | Zero or more Query::feature_flag specifying what features the QueryParser should support. Combine multiple values with bitwise-or (|) (default FLAG_DEFAULT).
  | default_prefix | The default term prefix to use (default none). For example, you can pass "A" when parsing an "Author" field.

Exceptions:

  | If | the query string can't be parsed, then Xapian::QueryParserError is thrown. You can get an English error message to report to the user by catching it and calling get_msg() on the caught exception. The current possible values (in case you want to translate them) are:

* Unknown range operation * parse error * Syntax: <expression> AND <expression> * Syntax: <expression> AND NOT <expression> * Syntax: <expression> NOT <expression> * Syntax: <expression> OR <expression> * Syntax: <expression> XOR <expression>

void Xapian::QueryParser::set_default_op | ( | Query::op | default_op | ) |

Set the default operator.

This operator is used to combine non-filter query items when no explicit operator is used.

The most useful values for this are OP_OR (the default) and OP_AND. OP_NEAR and OP_PHRASE can also be useful.

So for example, 'weather forecast' is parsed as if it were 'weather OR forecast' by default.

void Xapian::QueryParser::set_stemmer | ( | const Xapian::Stem & | stemmer | ) |

Set the stemmer.

This sets the stemming algorithm which will be used by the query parser. Note that the stemming algorithm will only be used according to the stemming strategy set by set_stemming_strategy(), which defaults to STEM_NONE. Therefore, to use a stemming algorithm, you will also need to call set_stemming_strategy() with a value other than STEM_NONE.

void Xapian::QueryParser::set_stemming_strategy | ( | stem_strategy | strategy | ) |

Set the stemming strategy.

This controls how the query parser will apply the stemming algorithm. The default value is STEM_NONE. The possible values are:

- STEM_NONE: Don't perform any stemming.
- STEM_SOME: Search for stemmed forms of terms except for those which start with a capital letter, or are followed by certain characters (currently: (/@<>=*[{" ), or are used with operators which need positional information. Stemmed terms are prefixed with 'Z'.
- STEM_ALL: Search for stemmed forms of all words (note: no 'Z' prefix is added).

Note that the stemming algorithm is only applied to words in probabilistic fields - boolean filter terms are never stemmed.

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

- xapian/queryparser.h