class Ferret::Search::PrefixQuery

Summary

A prefix query is like a TermQuery except that it matches any term with a specific prefix. PrefixQuery is expanded into a MultiTermQuery when submitted in a search.

Example

PrefixQuery is very useful for matching a tree structure category hierarchy. For example, let's say you have the categories;

"cat1/"
"cat1/sub_cat1"
"cat1/sub_cat2"
"cat2"
"cat2/sub_cat1"
"cat2/sub_cat2"

Lets say you want to match everything in category 2. You'd build the query like this;

query = PrefixQuery.new(:category, "cat2")
# matches => "cat2"
# matches => "cat2/sub_cat1"
# matches => "cat2/sub_cat2"

Public Class Methods

new(field, prefix, options = {}) → prefix-query click to toggle source

Create a new PrefixQuery to search for all terms with the prefix prefix in the field field. There is one option that you can set to change the behaviour of this query. :max_terms specifies the maximum number of terms to be added to the query when it is expanded into a MultiTermQuery. Let's say for example you search an index with a million terms for all terms beginning with the letter ā€œsā€. You would end up with a very large query which would use a lot of memory and take a long time to get results, not to mention that it would probably match every document in the index. To prevent queries like this crashing your application you can set :max_terms which limits the number of terms that get added to the query. By default it is set to 512.

static VALUE
frb_prq_init(int argc, VALUE *argv, VALUE self)
{
    return frb_mtq_init_specific(argc, argv, self, &prefixq_new);
}