7.13. grn_expr¶
Grn_expr is an object that searches records with specified conditions
and manipulates a database. It’s pronounced as gurun expression.
Conditions for searching records from a database can be represented by
conbining condition expressions such as equal condition expression
and less than condition expression with set operations such as
AND, OR and NOT. Grn_expr executes those conditions to
search records. You can also use advanced searches such as similar
search and near search by grn_expr. You can also use flexible full
text search. For example, you can control hit scores for specified
words and improve recall by re-searching with high-recall algolithm
dinamically. To determine whether re-searching or not, the number of
matched rescords is used.
There are three ways to create grn_expr:
Parsing Query syntax string.
Parsing Script syntax string.
Calling grn_expr related APIs.
Query syntax is for common search form in
Internet search site. It’s simple and easy to use but it has a
limitation. You can not use all condition expressions and set
operations in Query syntax. You can use
Query syntax with query option in
select.
Script syntax is ECMAScript like
syntax. You can use all condition expressions and set operations in
Script syntax. You can use
Script syntax with filter option and
scorer option in select.
You can use groonga as a library and create a grn_expr by calling grn_expr related APIs. You can use full features with calling APIs like Script syntax. Calling APIs is useful creating a custom syntax to create grn_expr. They are used in rroonga that is Ruby bindings of Groonga. Rroonga can create a grn_expr by Ruby’s syntax instead of parsing string.