From: Red Daly <reddaly@...>
Date: 2006-08-01T23:25:06+09:00
Subject: ActiveRecord: find_or_create with has_and_belongs_to_many -- unexpected behavior

I am attempting to use find_or_create on a foreign table with a 
has_and_belongs_to_many relationship with my current table.  I am doing 
the following:

term = school.terms.find_or_create_by_code("FALL06")

the queries in the log show the expected SELECT statement to query if 
there is a join table record between the school and term with code "FALL06":

SELECT * FROM term
INNER JOIN school_term ON term.id = school_term.term_id
WHERE (school_term.school_id = 1 )
   AND (term.`code` = 'FALL06' )
LIMIT 1

but the INSERT behavior does not include a join table insert if the 
SELECT does not find an appropriate record:

INSERT INTO term (`code`, `name_full`, `name_common`, `date_end`, 
`date_start`)
VALUES('FALL06', NULL, NULL, NULL, NULL)

I have resolved this by changing my original code to implement a 
uniqueness check in ruby:

term = school.terms.find_or_create_by_code("FALL06")
school.terms << term unless school.terms.any? do |i| i == term;

It seems like ActiveRecord and SQL should take care of that behavior 
rather than the ActiveRecord implementor and Ruby.  Am I missing 
something?  Is there another way to do what I want?

Also, I'm not sure if c.l.ruby is the best newsgroup, but I couldn't 
find a ruby on rails group.

Thanks Sincerely,
Red Daly