Class Ferret::Search::PrefixQuery
In: ext/r_search.c
Parent: Ferret::Search::Query

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"

Methods

new  

Public Class methods

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 "s". 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.

[Validate]