Hack for partial matches in Ferret

December 12, 2007 code 3 min read

I love ferret (the ruby port of Lucene, not the fuzzy little creatures, you sicko). But something I fight on every project is that ferret turns into a bear when you try to get it to do partial matches, like "ferr" matching "ferret" and "ferrari".

Ferret allows you to append an asterisk to your search query ("ferr*"), which works great, but we can’t expect our users to do that because damn Google 1 has set the expectation that search just works; I don’t need to use any funky syntax to find my pogs, Harry Potter gossip or BRATZ 2.

So, we can do this manually in code by appending an asterisk to anything users enter and problem solved, right? Not quite.

  • It breaks if you’re using the StemFilter, which allows you to match variations of words ("happy" would match "happiness" and "happiest")
  • It will only match partials on the last word that the user entered ("Ed Brad" won’t find "Edward Bradley")
  • Apparently the asterisk tells ferret that there has to be more characters, because full matches no longer work ("ferret*" won’t match "ferret")

So, here’s my hack.

Book.find_by_contents "(#{term})^2 OR (#{ {|t| t + "*" }.join(' ')})"

This ugly little thing will match exactly what the user entered (making use of stemming and all the magic that comes from it) and give it a little boost in the ranking, or match any part of any of the words entered, giving me partial matches.

I acknowledge that this is an ugly hack at the moment, and will break miserably if the user is any kind of a wizard that knows how to do advanced searches, but it works for now. I have no idea what kind of consequences this will have as far as search performance and such. The goal is to wrap this into a filter.

Any one else have any cleaver ideas for doing partial matches?

  1. Yes, Google, we love and hate you for raising the bar.
  2. We're talking normal users here, which excludes anyone that is reading this.
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avatar of Brandon Keepers I am Brandon Keepers, and I work at GitHub on making Open Source more approachable, effective, and ubiquitous. I tend to think like an engineer, work like an artist, dream like an astronaut, love like a human, and sleep like a baby.