I have an ActiveRecord called Name
which contains names in various Languages
.
class Name < ActiveRecord::Base
belongs_to :language
class Language < ActiveRecord::Base
has_many :names
Finding names in one language is easy enough:
Language.find(1).names.find(whatever)
But I need to find matching pairs where both language 1 and language 2 have the same name. In SQL, this calls for a simple self-join:
SELECT n1.id,n2.id FROM names AS n1, names AS n2
WHERE n1.language_id=1 AND n2.language_id=2
AND n1.normalized=n2.normalized AND n1.id != n2.id;
How can I do a query like this with ActiveRecord? Note that I need to find pairs of names (= both sides of the match), not just a list of names in language 1 that happens to match with something.
For bonus points, replace n1.normalized=n2.normalized
with n1.normalized LIKE n2.normalized
, since the field may contain SQL wildcards.
I'm also open to ideas about modeling the data differently, but I'd prefer to avoid having separate tables for each language if I can.
Try this:
ids = [1,2]
Name.all(:select => "names.id, n2.id AS id2",
:joins => "JOIN names AS n2
ON n2.normalized = names.normalized AND
n2.language_id != names.language_id AND
n2.language_id IN (%s)" % ids.join(','),
:conditions => ["names.language_id IN (?)", ids]
).each do |name|
p "id1 : #{name.id}"
p "id2 : #{name.id2}"
end
PS: Make sure you sanitize the parameters passed to the join condition.