# Why not merge :joins in with\_scope? **URL:** \ **Category:** Rails\ **Created:** [May 26, 2008, 5:25pm UTC](https://www.ruby-forum.com/t/why-not-merge-joins-in-with-scope/138681 "2008-05-26T17:25:21Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![macournoyer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e495f1/32.png) [@macournoyer](https://www.ruby-forum.com/u/macournoyer)\ **Post date:** [May 26, 2008, 5:25pm UTC](https://www.ruby-forum.com/t/why-not-merge-joins-in-with-scope/138681/1 "2008-05-26T17:25:21Z")
Hi, We’re chaining several named\_scope calls like this: Post.something\_with\_a\_join.another\_with\_a\_join And we found out the :joins in the scope aren’t merged. I’m wondering if there’s any reason why :joins aren’t merged but :conditions and :include are, see: > I know some join could be contradictory but they can also be required by the conditions. I have a patch ready for this but I’m waiting for some feedback before writing some tests and submitting it, maybe I’m missing something. Thanks, Marc ---
**Author:** ![macournoyer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e495f1/32.png) [@macournoyer](https://www.ruby-forum.com/u/macournoyer)\ **Post date:** [May 26, 2008, 5:30pm UTC](https://www.ruby-forum.com/t/why-not-merge-joins-in-with-scope/138681/2 "2008-05-26T17:30:06Z")
On 26 May 2008, at 16:24, macournoyer wrote: > but :conditions and :include are, see: > [http://github.com/rails/rails/tree/master/activerecord/lib/active\_record/base.rb#L1823](http://github.com/rails/rails/tree/master/activerecord/lib/active_record/base.rb#L1823) :joins comes in 2 forms. When :joins is like :include (ie an array of (possibly nested) association names, i don’t see why it couldn’t behave like :include. That usage is newish (last autumn?) so it could jus be an omission. In the other usage where :joins is an sql fragment then it’s rather more problematic (for doing things like removing duplicates etc…) Fred ---
**Author:** ![macournoyer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e495f1/32.png) [@macournoyer](https://www.ruby-forum.com/u/macournoyer)\ **Post date:** [May 26, 2008, 5:38pm UTC](https://www.ruby-forum.com/t/why-not-merge-joins-in-with-scope/138681/3 "2008-05-26T17:38:22Z")
You’re right, but by not merging :joins it fails in both cases: when it’s like include and as an sql fragment If we merge the :joins like described here: [http://blog.teksol.info/2008/5/26/why-are-activerecord-scopes-not-merged](http://blog.teksol.info/2008/5/26/why-are-activerecord-scopes-not-merged) , it will only fail in the later case, when it’s used a an sql fragment and both conflict. On May 26, 11:29 am, Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![macournoyer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e495f1/32.png) [@macournoyer](https://www.ruby-forum.com/u/macournoyer)\ **Post date:** [May 26, 2008, 5:41pm UTC](https://www.ruby-forum.com/t/why-not-merge-joins-in-with-scope/138681/4 "2008-05-26T17:41:55Z")
On 26 May 2008, at 16:34, francois.beausoleil wrote: > Shouldn’t the DB server intelligent enough to filter out duplicates in > that case ? Doesn’t sound like the sort of thing you could rely on across the board. ---
**Author:** ![macournoyer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e495f1/32.png) [@macournoyer](https://www.ruby-forum.com/u/macournoyer)\ **Post date:** [May 26, 2008, 5:39pm UTC](https://www.ruby-forum.com/t/why-not-merge-joins-in-with-scope/138681/5 "2008-05-26T17:39:33Z")
On 26 mai, 11:29, Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > :joins comes in 2 forms. When :joins is like :include (ie an array of > (possibly nested) association names, i don’t see why it couldn’t > behave like :include. That usage is newish (last autumn?) so it could > jus be an omission. In the other usage where :joins is an sql fragment > then it’s rather more problematic (for doing things like removing > duplicates etc…) Shouldn’t the DB server intelligent enough to filter out duplicates in that case ? Thanks! François ---
**Author:** ![macournoyer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e495f1/32.png) [@macournoyer](https://www.ruby-forum.com/u/macournoyer)\ **Post date:** [May 26, 2008, 5:44pm UTC](https://www.ruby-forum.com/t/why-not-merge-joins-in-with-scope/138681/6 "2008-05-26T17:44:52Z")
On 26 May 2008, at 16:37, macournoyer wrote: > You’re right, but by not merging :joins it fails in both cases: when > it’s like include and as an sql fragment > > If we merge the :joins like described here: > [http://blog.teksol.info/2008/5/26/why-are-activerecord-scopes-not-merged](http://blog.teksol.info/2008/5/26/why-are-activerecord-scopes-not-merged) > , it will only fail in the later case, when it’s used a an sql > fragment and both conflict. I think you’d probably want to base yourself on what :include does (in fact you could probably reuse the merge\_includes code), as you need to handle the fact that you can say :joins =\> :foo or :joins =\> [:foo] and things like that Fred ---
**Author:** ![macournoyer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e495f1/32.png) [@macournoyer](https://www.ruby-forum.com/u/macournoyer)\ **Post date:** [May 26, 2008, 7:24pm UTC](https://www.ruby-forum.com/t/why-not-merge-joins-in-with-scope/138681/7 "2008-05-26T19:24:03Z")
Hey, I’m probably the last person to touch the :joins =\> :association style syntax so I’d like to chime in with a warning here. The change proposed in: [http://blog.teksol.info/2008/5/26/why-are-activerecord-scopes-not-merged](http://blog.teksol.info/2008/5/26/why-are-activerecord-scopes-not-merged) sets off alarm bells for me. See the following line: > What that line does is ensure that your joins {:like =\> :this}, :or, [:like, :this] will be treated as an _inner_ join. If you just concatenate the :joins together into a string you’ll break those semantics. I know Fred has already brought it to your attention that you should base your code off the way that :includes are handled (merge\_includes) but I just wanted to add some weight to that. And as for “why doesn’t it already do what it ought to?”… I’m pretty sure that when I reworked that stuff I didn’t actually _remove_ anything so I kind of hope it never merged joins in scopes in the first place… if I did remove something critical then I shall quietly flog myself 😛 Regards, Trevor On 5/26/08, Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > , it will only fail in the later case, when it’s used a an sql > > > > > (possibly nested) association names, i don’t see why it couldn’t > > > > > > > by the conditions. ## – Trevor S. [http://somethinglearned.com](http://somethinglearned.com)