[Rails-core] Behavior of first_or_create

On Tue, Jul 24, 2012 at 2:43 PM, Matt Jones wrote:

I just ran across a weird glitch (IMHO) in find_or_create. The arguments
passed to it are *not* added to the conditions for the 'first' part. This
is odd, given that it's intended to replace find_or_create_by_* methods,
which *did* use the specified values as conditions.

I'm unsure on whether this behavior is entirely undesirable, but it's
definitely not what I had expected in my use case (ensuring that a join
table record exists). Perhaps there should be a variant
(find_or_create_exactly, perhaps?) that uses the supplied attributes as
additional conditions.

If nothing else, the documentation should be updated to reflect this
scenario - the last case in the examples *almost* describes this scenario,
but the block form used there makes it unclear what:

User.where(:first_name => 'Scarlett').first_or_create(:last_name =>
"O'Hara")

would do.

I also found that DataMapper implements the behavior I was expecting in
their first_or_create method:

https://github.com/datamapper/dm-core/blob/master/lib/dm-core/model.rb#L448

Thoughts?

--Matt Jones


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On Jul 24, 2012, at 4:04 PM, Andrés Mejía wrote:

I would definitely expect

User.where(:first_name => 'Scarlett').first_or_create(:last_name => "O'Hara")

to call

User.create(:first_name => 'Scarlett', :last_name => "O'Hara")

if that's not what's happening then I think it's a bug and should be fixed. Matt, do you have a minimal app that shows the problem? I would like to write a test case for Rails that shows this strange behavior.

On 24/07/12 21:29, Matt Jones wrote:
Nope, that's not exactly what I observed; I'll try again. That code *does* call the create correctly, if there are no users with the correct first_name. The confusing part to me was that it wasn't quite the same as this:

User.where(:first_name => 'Scarlett').find_or_create_by_last_name("O'Hara")

The latter includes a condition on last_name in the find, where the former does not.

On Jul 24, 2012, at 5:42 PM, Jon Leighton wrote:
This behaviour is intentional. The dynamic version did actually previously take an options hash of stuff that would get passed to create. So:

User.where(:first_name => 'Scarlett').find_or_create_by_last_name("O'Hara", :age => 32)

would do:

User.where(:first_name => "Scarlett", :last_name => "O'Hara")

and then:

User.create(:first_name => "Scarlett", :last_name => "O'Hara", :age => 32)

I believe the rationale is simply that you can put all of your conditions in a where()