Question

How can I modify a where/like condition on a search query in Rails:

find(:all, :conditions => ["lower(name) LIKE ?", "%#{search.downcase}%"])

so that the results are matched irrespective of accents? (eg métro = metro). Because I’m using utf8, I can’t use “to_ascii”. Production is running on Heroku.

Answer 1

Proper solution

Since PostgreSQL 9.1 you can just:

CREATE EXTENSION unaccent;

Provides a function unaccent(), doing what you need (except for lower(), just use that additionally if needed). Read the manual about this extension.

More about unaccent and indexes:

• Does PostgreSQL support "accent insensitive" collations?

Poor man’s solution

If you can’t install unacccent, but are able to create a function. I compiled the list starting here and added to it over time. It is comprehensive, but hardly complete:

CREATE OR REPLACE FUNCTION lower_unaccent(text)
  RETURNS text
  LANGUAGE sql IMMUTABLE STRICT AS
$func$
SELECT lower(translate($1
     , '¹²³áàâãäåāăąÀÁÂÃÄÅĀĂĄÆćčç©ĆČÇĐÐèéêёëēĕėęěÈÊËЁĒĔĖĘĚ€ğĞıìíîïìĩīĭÌÍÎÏЇÌĨĪĬłŁńňñŃŇÑòóôõöōŏőøÒÓÔÕÖŌŎŐØŒř®ŘšşșߊŞȘùúûüũūŭůÙÚÛÜŨŪŬŮýÿÝŸžżźŽŻŹ'
     , '123aaaaaaaaaaaaaaaaaaacccccccddeeeeeeeeeeeeeeeeeeeeggiiiiiiiiiiiiiiiiiillnnnnnnooooooooooooooooooorrrsssssssuuuuuuuuuuuuuuuuyyyyzzzzzz'
     ));
$func$;

Your query should work like that:

find(:all, :conditions => ["lower_unaccent(name) LIKE ?", "%#{search.downcase}%"])

For left-anchored searches, you can use an index on the function for very fast results:

CREATE INDEX tbl_name_lower_unaccent_idx
  ON fest (lower_unaccent(name) text_pattern_ops);

For queries like:

SELECT * FROM tbl WHERE (lower_unaccent(name)) LIKE 'bob%';

Or use COLLATE "C". See:

• PostgreSQL LIKE query performance variations
• Is there a difference between text_pattern_ops and COLLATE "C"?