TSEARCH2: disable stemming in indexes and triggers

From: Erwin Moller <erwin(at)darwine(dot)nl>
To: pgsql-general(at)postgresql(dot)org
Subject: TSEARCH2: disable stemming in indexes and triggers
Date: 2007-05-31 11:01:19
Message-ID: 1180609279.22968.3291.camel@Willow
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Hi all,

I installed TSEARCH2 on Postgres8.1 (Debian).
It runs all fine.
I have 2 tables indexed, and created triggers to keep the vectorcolumns
up
to date.

However, the text I indexed is a mix of Dutch and English and German.
The default stemmingprocess is an annoyance for me.
I would like to disable it.
I found out that using 'simple' instead of 'default' when using
to_tsvector() does excactly that, but I don't know how to change my
triggers and indexes to keep doing the same (using 'simple').

My TSEARCH2 and trigger-skills are developing, but I lack the confidence
to
change thing on the site (which is live), so I thought I check in here.

I have a table named tblvacature, that contains a bunch of columns that
need
to be indexed by TSEARCH.

This is what I did (and it works, except for the fact I want to disable
stemming)

1) ALTER TABLE tblvacature ADD COLUMN idxFTI tsvector;
2) UPDATE tblvacature SET idxFTI=to_tsvector('simple',
coalesce(title,'') ||' '||
coalesce(shortintro,'') ||' '||
coalesce(werkgever,'') ||' '||
coalesce(vacaturesteller,'') ||' '||
coalesce(standplaats,'') ||' '||
coalesce(divafdelingwerkgever,'') );

3) VACUUM FULL ANALYZE;

4) CREATE INDEX idxFTIvacture_idx ON tblvacature USING gist(idxFTI);

5) VACUUM FULL ANALYZE;

6) CREATE TRIGGER tsvectorupdate_vacature BEFORE UPDATE OR INSERT ON
tblvacature FOR EACH ROW EXECUTE
PROCEDURE tsearch2(idxFTI, title, shortintro, werkgever,
vacaturesteller,
standplaats, divafdelingwerkgever);

Step 2 worked fine: no stemming.
But how do I cange my step6 (trigger) so it keeps using 'simple'?
Or do I have to change the index itself (step4) too? Or both?

Please advise.

Thanks for your time.

Regards,
Erwin Moller

-----------------------
PS: This is my first posting to pgsql-general: if I screw something up,
please let me know.

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