Rails - Dec 2005 - I don''t even know how to ask the question (4 lines of code)

I create a hash using this line of code     @x = Account.find(:all)

I then want to go through each element in turn and add a key value  
pair to the end of it.  I thought this would work, but it does not.

@x.each do |a|

a.merge({"balance"=>50}

I used merge because I thought ''a'' would be a hash  (how do
you find
out the type of an object?)

I then guess it was an array so I tried both <<   and +    no success.

What should I be doing?

On 12/30/05, Bruce Balmer <brucebalmer@mac.com>
wrote:
> I create a hash using this line of code     @x = Account.find(:all)
>
> I then want to go through each element in turn and add a key value
> pair to the end of it.  I thought this would work, but it does not.
>
> @x.each do |a|
>
> a.merge({"balance"=>50}
>
> I used merge because I thought ''a'' would be a hash  (how
do you find
> out the type of an object?)
>
> I then guess it was an array so I tried both <<   and +    no
success.
>
> What should I be doing?
Account.find(:all) returns an Array of ActiveRecord instances.
You can determine this with inspect. e.g.:
logger.debug @x.inspect
..which will place the details in the log file.

@x.each do |a|
# a is an ActiveRecord object here.
# If ''balance'' is already an attribute of the object, you can
say:
a.balance = 50
end

Your code would work if each entry in @x was indeed a Hash, but that''s
not the case with the ActiveRecord finders.

On Fri, Dec 30, 2005 at 04:58:06PM -0700, Bruce Balmer
wrote:
> I create a hash using this line of code     @x = Account.find(:all)
By my understanding, @x will be an array after this line.
> I then want to go through each element in turn and add a key value  
> pair to the end of it.  I thought this would work, but it does not.
> 
> @x.each do |a|
> 
> a.merge({"balance"=>50}
Assuming that what you''re trying to do is set the
''balance'' attribute on all
of your accounts to 50, you could try

@x.each { |a| a.balance = 50 }
> I used merge because I thought ''a'' would be a hash
Each ''a'' should be an object of type Account.
> (how do you find  
> out the type of an object?)
a.class

- Matt

-- 
"[the average computer user] has been served so poorly that he expects his
system to crash all the time, and we witness a massive worldwide
distribution of bug-ridden software for which we should be deeply ashamed."
		-- Edsger Dijkstra

The variable a will hold an Account object.  I think you want to do
something like

Account.find(:all).each do | a |
  a.balance = 50
end

(maybe you want to save the accounts also, etc.)

In answer to your other question, you can use functions like is_a? or
.class.name to check types of objects:

Account.find(:all).each do | a |
  is_acct = (a.is_a? Account)
  # is_acct is now true
  typename = a.class.name
  # typename holds ''Account''
end


On 12/30/05, Bruce Balmer <brucebalmer@mac.com>
wrote:
>
> I create a hash using this line of code     @x = Account.find(:all)
>
> I then want to go through each element in turn and add a key value
> pair to the end of it.  I thought this would work, but it does not.
>
> @x.each do |a|
>
> a.merge({"balance"=>50}
>
> I used merge because I thought ''a'' would be a hash  (how
do you find
> out the type of an object?)
>
> I then guess it was an array so I tried both <<   and +    no
success.
>
> What should I be doing?
>
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
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Thanks.  I now guess that a is neither a hash nor an array but rather  
it is just an object of type object. Is that true?

My problem is that a does not currently have a balance attribute and  
so I wish to extend the object to include one.  Is this possible?  If  
not, how can I convert my object to a hash so I can add this  
attribute ''balance'' that I require.

bruce






On 30-Dec-05, at 5:36 PM, Michael Smedberg wrote:
> The variable a will hold an Account object.  I think you want to do  
> something like
>
> Account.find(:all).each do | a |
>   a.balance = 50
> end
>
> (maybe you want to save the accounts also, etc.)
>
> In answer to your other question, you can use functions like is_a?  
> or .class.name to check types of objects:
>
> Account.find(:all).each do | a |
>   is_acct = (a.is_a? Account)
>   # is_acct is now true
>   typename = a.class.name
>   # typename holds ''Account''
> end
>
>
> On 12/30/05, Bruce Balmer <brucebalmer@mac.com> wrote:
> I create a hash using this line of code     @x = Account.find(:all)
>
> I then want to go through each element in turn and add a key value
> pair to the end of it.  I thought this would work, but it does not.
>
> @ x.each do |a|
>
> a.merge({"balance"=>50}
>
> I used merge because I thought ''a'' would be a hash  (how
do you find
> out the type of an object?)
>
> I then guess it was an array so I tried both <<   and +    no
success.
>
> What should I be doing?
>
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
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On Fri, Dec 30, 2005 at 05:51:35PM -0700, Bruce Balmer
wrote:
> Thanks.  I now guess that a is neither a hash nor an array but rather  
> it is just an object of type object. Is that true?
No, from the code in your last post, each ''a'' will be an
object of type
Account, which should be a descendant of ActiveRecord::Base.
> My problem is that a does not currently have a balance attribute and  
> so I wish to extend the object to include one.  Is this possible?  If  
> not, how can I convert my object to a hash so I can add this  
> attribute ''balance'' that I require.
Keep well away from the idea of hashes.  You don''t want them.  If you
need
to add a new attribute, you can just add it to the database table which
backs the Account class (if you want to store that value in the database),
or else add an :attr_accessor balance to your class definition, which will
create the necessary accessor methods to manipulate the instance variable
@balance in your Account objects.

If the previous paragraph was complete gibberish to you, you might be well
served to pick up a copy of the pickaxe and learn some more Ruby programming
(or else my explanatory skills have gone badly downhill lately).  I
can''t
imagine doing much at all with Rails without understanding the underlying
Ruby code.

- Matt

Mathew:

I did understand what you said (except why  I would want to avoid  
hashes). The real reason I wanted to avoid hashes (my reason) was  
that I felt that this ought to be possible through a proper object  
oriented approach.  Your answer is wonderful. Exactly what my  
instincts were telling me I should search for but which my brain  
could not generate. Now  you have said it, your explanation is  
totally and obvious.

Thanks so much. I really appreciate your help with this.

bruce


On 30-Dec-05, at 6:08 PM, Matthew Palmer wrote:
> On Fri, Dec 30, 2005 at 05:51:35PM -0700, Bruce Balmer wrote:
>> Thanks.  I now guess that a is neither a hash nor an array but rather
>> it is just an object of type object. Is that true?
>
> No, from the code in your last post, each ''a'' will be an
object of
> type
> Account, which should be a descendant of ActiveRecord::Base.
>
>> My problem is that a does not currently have a balance attribute and
>> so I wish to extend the object to include one.  Is this possible?  If
>> not, how can I convert my object to a hash so I can add this
>> attribute ''balance'' that I require.
>
> Keep well away from the idea of hashes.  You don''t want them.  If
> you need
> to add a new attribute, you can just add it to the database table  
> which
> backs the Account class (if you want to store that value in the  
> database),
> or else add an :attr_accessor balance to your class definition,  
> which will
> create the necessary accessor methods to manipulate the instance  
> variable
> @balance in your Account objects.
>
> If the previous paragraph was complete gibberish to you, you might  
> be well
> served to pick up a copy of the pickaxe and learn some more Ruby  
> programming
> (or else my explanatory skills have gone badly downhill lately).  I  
> can''t
> imagine doing much at all with Rails without understanding the  
> underlying
> Ruby code.
>
> - Matt
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails