Generated sql for has_many :through relation wrong when used with STI

Imported from Lighthouse. Original ticket at: http://rails.lighthouseapp.com/projects/8994/tickets/6608 Created by eli.b - 2011-03-23 03:39:09 UTC

Consider these models:

`class First < ActiveRecord::Base`

has_many :tags

has_many :thirds, :through => :tags

end

class Second < ActiveRecord::Base end

class Third < Second

has_many :tags

has_many :firsts, :through => :tags

end

class Tag < ActiveRecord::Base

belongs_to :first

belongs_to :third

end

In other words, we have a has_many :through 'tag-style' relationship, but with one of the models (Third) being an STI inheriting from another (Second). Say I wanted to do a join to see all instances of Third for some value of First: @thirds = Third.joins(:firsts).where("first.id = 2")

This will work as expected; the generated sql (via to_sql) being:

SELECT seconds.* FROM seconds INNER JOIN tags ON seconds.id = tags.third_id INNER JOIN firsts ON firsts.id = tags.first_id WHERE seconds.type = 'Third' AND (first.id = 1)

This doesn't work in the other direction: @firsts = First.joins(:thirds).where("second.id = 2")

The SQL generated being:

SELECT firsts.* FROM firsts INNER JOIN tags ON firsts.id = tags.first_id INNER JOIN seconds ON seconds.type = 'Third' WHERE (second.id = 2)

This results in tag duplication due to the fact that :seconds are not joined correctly with the tag table as in the first case above (see third line of sql statement in each case). All firsts with tags will show up in the resulting table, the WHERE clause being entirely ineffectual.

If something different needs to be stated in the ActiveRecord::Query statements above, it is not documented...

This is all using Rails 3.0.5.