# 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.
void | set_max_wildcard_expansion (Xapian::termcount limit)
| Specify the maximum expansion of a wildcard term.
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, bool exclusive)
| 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*). Currently you can't use wildcards with boolean filter prefixes, or in a phrase (either an explicitly quoted one, or one implicitly generated by hyphens or other punctuation). 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.

  Currently FLAG_PARTIAL doesn't do anything if the final word in the query has a boolean filter prefix, or if it is in a phrase (either an explicitly quoted one, or one implicitly generated by hyphens or other punctuation). It also doesn't do anything if if the final word is part of a value range.

  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(). The default flags are FLAG_PHRASE|FLAG_BOOLEAN|FLAG_LOVEHATE. Added in Xapian 1.0.11.

## Member Function Documentation

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

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
  | exclusive | If true, each document can have at most one term with this prefix, so multiple filters with this prefix should be combined with OP_OR. If false, each document can have multiple terms with this prefix, so multiple filters should be combined with OP_AND, like happens with filters with different prefixes. [default: true]

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_database | ( | const Database & | db | ) |

Specify the database being searched.

Parameters:

  | db | The database to use for wildcard expansion (FLAG_WILDCARD and FLAG_PARTIAL), spelling correction (FLAG_SPELLING_CORRECTION), and synonyms (FLAG_SYNONYM, FLAG_AUTO_SYNONYMS, and FLAG_AUTO_MULTIWORD_SYNONYMS).

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

Set the default operator.

Parameters:

  | default_op | The operator to use 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_max_wildcard_expansion | ( | Xapian::termcount | limit | ) |

Specify the maximum expansion of a wildcard term.

Note: you must also set FLAG_WILDCARD for wildcard expansion to happen.

Parameters:

  | limit | The maximum number of terms each wildcard in the query can expand to, or 0 for no limit (which is the 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.

Parameters:

  | stemmer | The Xapian::Stem object to set.

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

Set the stemming strategy.

This controls how the query parser will apply the stemming algorithm. Note that the stemming algorithm is only applied to words in probabilistic fields - boolean filter terms are never stemmed.

Parameters:

  strategy

  The strategy to use - possible values are:
  - STEM_NONE: Don't perform any stemming (the default).
  - 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).

void Xapian::QueryParser::set_stopper | ( | const Stopper * | stop = `NULL` | ) |

Set the stopper.

Parameters:

  | stop | The Stopper object to set (default NULL, which means no stopwords).

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

- xapian/queryparser.h