Rails core - Sep 2011 - Rails 3.1, has_many relationship and new records problem

Supose I have a simple has_many relationship betwen model_1 and
model_2:

class Model1 < ActiveRecord::Base
    has_many :models_2
end

class Model2 < ActiveRecord::Base
    belongs_to :model_1
end

Now, I create an instance of Model2 through the relationship:

irb>m1 = Model1.first
irb>m2 = m1.models_2.new

Now, if I want to ask for the size of the relationship, there''s a huge
difference between Rails 3.0.x and Rails 3.1.

Following the previous example, in Rails 3.0.x i get:

irb>m1.models_2.any?
irb>false
irb>m1.models_2.size
irb>0

This means, new objects are not being considered

This exact same query in Rails 3.1:

irb>m1.models_2.any?
irb>true #OMG!!
irb>m1.models_2.size
irb>1
So, the solution is:

irb>m1.models_2.all.any?
irb>false
irb>m1.models_2.all.size
irb>0

If I have to change ALL my relationships with .all, I''m in a big
trouble... am I missing something?
Thank you very much.

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On Thu, Sep 22, 2011 at 11:12 AM, Daro <dariobarr@gmail.com>
wrote:
> Supose I have a simple has_many relationship betwen model_1 and
> model_2:
>
> class Model1 < ActiveRecord::Base
>    has_many :models_2
> end
>
> class Model2 < ActiveRecord::Base
>    belongs_to :model_1
> end
>
> Now, I create an instance of Model2 through the relationship:
>
> irb>m1 = Model1.first
> irb>m2 = m1.models_2.new
>
> Now, if I want to ask for the size of the relationship, there''s a
huge
> difference between Rails 3.0.x and Rails 3.1.
>
> Following the previous example, in Rails 3.0.x i get:
>
> irb>m1.models_2.any?
> irb>false
> irb>m1.models_2.size
> irb>0
>
> This means, new objects are not being considered
>
> This exact same query in Rails 3.1:
>
> irb>m1.models_2.any?
> irb>true #OMG!!
> irb>m1.models_2.size
> irb>1
> So, the solution is:
>
> irb>m1.models_2.all.any?
> irb>false
> irb>m1.models_2.all.size
> irb>0
>
> If I have to change ALL my relationships with .all, I''m in a big
> trouble... am I missing something?
> Thank you very much.
Looking a
thttps://github.com/rails/rails/blob/v3.1.0/activerecord/lib/active_record/relation.rb#L141-143
(and the same in v3.0.10, for example) I can''t figure out why that
isn''t the same, since the code is pretty much the same, so I''m
probably missing something.

That said, you have 3 ways of querying the size of an ActiveRecord relation:

* #length will load all the objects into an array (unless they are
already loaded) and then return the array''s size.
* #count will force a DB count and return that result, without loading
the model instances into memory.
* #size will, if the objects are already loaded in an array, return
the #length, or otherwise call #count.

So you don''t need to force an "all", that will load your
objects in
memory. Just calling #count should do.

Cheers,
-foca
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I believe that this is a rails 3.0 bug.

In both 3.0 and 3.1 ActiveRecord::Relation''s #build is an alias for
#new.
But somehow, in rails 3.0 this behaviour is not the same, #build will
increase the "size counter" and #new will not.

This was probably fixed in rails 3.1.

Everton Moreth



2011/9/22 Nicolás Sanguinetti <hi@nicolassanguinetti.info>
> On Thu, Sep 22, 2011 at 11:12 AM, Daro <dariobarr@gmail.com> wrote:
> > Supose I have a simple has_many relationship betwen model_1 and
> > model_2:
> >
> > class Model1 < ActiveRecord::Base
> >    has_many :models_2
> > end
> >
> > class Model2 < ActiveRecord::Base
> >    belongs_to :model_1
> > end
> >
> > Now, I create an instance of Model2 through the relationship:
> >
> > irb>m1 = Model1.first
> > irb>m2 = m1.models_2.new
> >
> > Now, if I want to ask for the size of the relationship,
there''s a huge
> > difference between Rails 3.0.x and Rails 3.1.
> >
> > Following the previous example, in Rails 3.0.x i get:
> >
> > irb>m1.models_2.any?
> > irb>false
> > irb>m1.models_2.size
> > irb>0
> >
> > This means, new objects are not being considered
> >
> > This exact same query in Rails 3.1:
> >
> > irb>m1.models_2.any?
> > irb>true #OMG!!
> > irb>m1.models_2.size
> > irb>1
> > So, the solution is:
> >
> > irb>m1.models_2.all.any?
> > irb>false
> > irb>m1.models_2.all.size
> > irb>0
> >
> > If I have to change ALL my relationships with .all, I''m in a
big
> > trouble... am I missing something?
> > Thank you very much.
>
> Looking a thttps://
>
github.com/rails/rails/blob/v3.1.0/activerecord/lib/active_record/relation.rb#L141-143
> (and the same in v3.0.10, for example) I can''t figure out why that
> isn''t the same, since the code is pretty much the same, so
I''m
> probably missing something.
>
> That said, you have 3 ways of querying the size of an ActiveRecord
> relation:
>
> * #length will load all the objects into an array (unless they are
> already loaded) and then return the array''s size.
> * #count will force a DB count and return that result, without loading
> the model instances into memory.
> * #size will, if the objects are already loaded in an array, return
> the #length, or otherwise call #count.
>
> So you don''t need to force an "all", that will load your
objects in
> memory. Just calling #count should do.
>
> Cheers,
> -foca
>
> > --
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Groups
> "Ruby on Rails: Core" group.
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> >
> >
>
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>
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This is a real problem, waiting for news

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On Thu, 2011-09-22 at 07:12 -0700, Daro wrote:
> If I have to change ALL my relationships with .all, I''m in a big
> trouble... am I missing something?
> Thank you very much.
I can confirm what you have described: https://gist.github.com/1248588

In 3.0 there were inconsistencies between calling ''new'' and
''build'' on
an association. I consider this a bug. In 3.1 the inconsistencies are
tidied up, resulting in the behaviour you describe.

If you want to issue a COUNT query to the db, use #count rather than
#size.

Cheers

-- 
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