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ActiveRecord generates invalid SQL when eager loading a hmt association with an order
Given:
class Author < ActiveRecord::Base
has_many :posts
has_many :comments_desc, :through => :posts, :source => :comments, :order => 'comments.id DESC'
end
Running:
Author.first(:include => :comments_desc)
Will generate the following invalid SQL:
SELECT "posts".* FROM "posts" WHERE ("posts".author_id = 1) ORDER BY comments.id DESC
This issue was not present in 2.3.5 but occurs in 2.3.9.
I've attached a failing test case which demonstrates this issue.
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eager-load-hmt-with-order.diff
1.26 KB
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Ryan Wallace- No changes were found…
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Ryan Wallace
The issue seems to have been introduced in this commit:
http://github.com/rails/rails/commit/0963774c0a6a58ba13ac0ff4763527...Though it looks like before this commit Rails would generate valid SQL, but the order option would not be respected (therefore this test still fails in Rails 2.3.5 though for a different reason).
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Ryan Wallace
I'm thinking it might make sense to fall back to a table join strategy (as mentioned in the ActiveRecord::AssociationPreload documentation) though I'm not sure how to do this yet. Let me know if I'm way off base on this.
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Ryan Wallace
- Tag changed from 2.3.9 to 2.3.9, activerecord, eager_loading, has_many_through
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Marcelo GiorgiHi Ryan,
I've just implement a patch for this.
My work was based on your test, so I've added 2 patch files, 1 with your test (where you are the author), and the second one which is the fix I've implemented.
This patches applies cleanly on 2-3-stable
Any suggestions are welcome.
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Marcelo Giorgi
- Assigned user set to Santiago Pastorino
- Tag changed from 2.3.9, activerecord, eager_loading, has_many_through to 2.3.9, activerecord, eager_loading, has_many_through, patched
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Ryan Wallace
Hi Marcelo,
Thanks for drafting up a patch! I did a bit of experimenting and I've found one situation where invalid SQL will still be generated:
class Author < ActiveRecord::Base has_many :posts has_many :comments_desc, :through => :posts, :source => :comments, :order => 'body DESC' end Author.first(:include => :comments_desc)Basically, if you don't specify the tables name in the order clause, the SQL will be invalid.
Do you think we should cover this case too or just make a note somewhere? My opinion is that it would be okay to leave it like this. It is a good practice to provide the table name in the order clause anyhow.
Ryan
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Santiago Pastorino- Milestone set to 2.3.10
- State changed from new to open
- Assigned user changed from Santiago Pastorino to Aaron Patterson
- Importance changed from to Low
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Marcelo Giorgi
- Assigned user changed from Aaron Patterson to Santiago Pastorino
Hi Ryan,
I think the bug that you found is a different problem, in fact I think it is a more general issue of Rails. As you mentioned it is arguable that the developer should include the table name explicitly in the order clause...
Also, if you look into the documentation (http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassM..., under the title 'Eager loading of associations', this behavior is already documented, where it says:
...You must disambiguate column references for this fallback to happen, for example :order => 'author.name DESC' will work but :order => "name DESC" will not...
Just to keep the commit aligned with the original intention of the problem at hand, perhaps, we can create a new ticket to discuss this other issue, do you agree ?
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Ryan Wallace
Oh perfect. Perhaps I should have read the documentation before asking for that case to be documented! +1 for this patch from me. Small, simple, and effective.
Thanks again Marcelo.
Ryan
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Patrick Campbell
Tested with environment ree-1.8.7-2010.01.
The test passed successfully and the implementation makes sense to me. Also, I agree that the order clause must have the attributes fully qualified when there is room for ambiguity.
+1
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Santiago Pastorino
- Assigned user changed from Santiago Pastorino to Aaron Patterson
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Andrea Campi- Tag changed from 2.3.9, activerecord, eager_loading, has_many_through, patched to 2.3.9, activerecord, eager_loading, has_many_through, patch
bulk tags cleanup