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Date: Thu, 18 Oct 2012 05:56:06 -0700 (PDT)
From: ChuckE <honeyryderch...@gmail.com>
To: rubyonrails-core@googlegroups.com
Message-Id: <0af0aefc-4d31-4de0-acbe-07f6ce3f4e29@googlegroups.com>
Subject: ActiveRecord: updating an association of an already persisted
 instance in memory without making the update persist right away. Is this
 possible?
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Hi,

I have ClassA, which has many objects of ClassB. Let's say that the 
dependency of that relationship is of the destroy kind:

class ClassA < ActiveRecord::Base
    has_many :class_bs, :dependency => :destroy
end
class ClassB < ActiveRecord::Base
    belongs_to :class_a
end

Now let's say I already have a persisted instance of ClassA, and this 
instance has also associated persisted objects:

   a = ClassA.first
   a.persisted #=> true
   a.class_bs.length #=> >1
   a.class_bs,all?{|b|b.persisted?} #=> true

So now, I would like to replace my associated class_bs with a new 
collection of only one element, which is not persisted. I would like to 
keep this only in memory, until I save the parent (or its child, for all I 
care):

   new_bs = [ClassB.new]
   new_bs.all?{|b| b.new_record? } #=> true
   a.class_bs = new_bs
   a.class_bs.all?{|b| b.new_record?} #=> true
   a.save
   a.class_bs.all?{|b| b.new_record?} #=> false

Problem is, the way it works, step 4 will return "false" instead of true. 
That is, as soon as I assign something to an already persisted parent, the 
new associations are stored right away (unless they are invalid). This is 
something that I don't like, because I may want to associate a to another 
object x, and I want to validate everything before I persist the changes, 
but the way it works, as soon as I get to x, changes were already made. Is 
there a way to do this in AR? and still keep the dependency => destroy? 

Thanks in advance

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Hi,<br><br>I have ClassA, which has many objects of ClassB. Let's say that =
the dependency of that relationship is of the destroy kind:<br><br>class Cl=
assA &lt; ActiveRecord::Base<br>&nbsp;&nbsp;&nbsp; has_many :class_bs, :dep=
endency =3D&gt; :destroy<br>end<br>class ClassB &lt; ActiveRecord::Base<br>=
&nbsp;&nbsp;&nbsp; belongs_to :class_a<br>end<br><br>Now let's say I alread=
y have a persisted instance of ClassA, and this instance has also associate=
d persisted objects:<br><br>&nbsp;&nbsp; a =3D ClassA.first<br>&nbsp;&nbsp;=
 a.persisted #=3D&gt; true<br>&nbsp;&nbsp; a.class_bs.length #=3D&gt; &gt;1=
<br>&nbsp;&nbsp; a.class_bs,all?{|b|b.persisted?} #=3D&gt; true<br><br>So n=
ow, I would like to replace my associated class_bs with a new collection of=
 only one element, which is not persisted. I would like to keep this only i=
n memory, until I save the parent (or its child, for all I care):<br><br>&n=
bsp;&nbsp; new_bs =3D [ClassB.new]<br>&nbsp;&nbsp; new_bs.all?{|b| b.new_re=
cord? } #=3D&gt; true<br>&nbsp;&nbsp; a.class_bs =3D new_bs<br>&nbsp;&nbsp;=
 a.class_bs.all?{|b| b.new_record?} #=3D&gt; true<br>&nbsp;&nbsp; a.save<br=
>&nbsp;&nbsp; a.class_bs.all?{|b| b.new_record?} #=3D&gt; false<br><br>Prob=
lem is, the way it works, step 4 will return "false" instead of true. That =
is, as soon as I assign something to an already persisted parent, the new a=
ssociations are stored right away (unless they are invalid). This is someth=
ing that I don't like, because I may want to associate a to another object =
x, and I want to validate everything before I persist the changes, but the =
way it works, as soon as I get to x, changes were already made. Is there a =
way to do this in AR? and still keep the dependency =3D&gt; destroy? <br><b=
r>Thanks in advance<br>
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