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From Ryszard Szopa <>
Subject solr and approximate string matching
Date Thu, 20 Aug 2009 19:01:45 GMT

I've been using Solr for some time in the simplest possible way (as a
backend to a search engine for English documents) and I've been really
happy about it. However, now I need to do something which is a bit
non-standard, and unfortunately I am desperately stuck. To make things
more complicated, I am using solr in a Django application through
Haystack [], but I am pretty sure that
there's no funny business going on between haystack and solr.

So, we have a database of movies and series, and as the data comes
from many sources of varying reliability, we'd like to be able to do
fuzzy string matching on the titles of episodes (the default matching
mechanisms operate on word levels, which is not good enough for short
strings, like titles). I had used n-grams approximate matching in the
past, and I was very happy to find that Lucene (and Solr) supports
something like this out of the box.

I assumed that I need a special field type for this, so I added the
following field-type to my schema.xml:

     <analyzer type="index">
       <filter class="solr.LowerCaseFilterFactory"/>

and changed the appropriate field in the schema to:

<field name="title" type="trigrams" indexed="true" stored="true"
multiValued="false" />

However, this is not working as I expected. The query analysis looks
correctly, but I don't get any results, which makes me believe that
something happens at index time (ie. the title is indexed like a
default string field instead of trigram field).

Moreover, I would like to be able to do something more. I'd like to
lowercace the string, remove all punctuation marks and spaces, remove
English stopwords and THEN change the string into trigrams. However,
the filters are applied only after the string has been tokenized...

Could you please suggest me any solution to this problem?

Thanks in advance for your answers.

 -- Ryszard Szopa


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