# Maintaining non persisted data

**URL:** <https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033>\
**Category:** Rails\
**Created:** [October 10, 2009, 2:12am UTC](https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033 "2009-10-10T02:12:28Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![cristie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a3d4f5/32.png) [@cristie](https://www.ruby-forum.com/u/cristie)\
**Post date:** [October 10, 2009, 2:12am UTC](https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033/1 "2009-10-10T02:12:28Z")

</div>

Hi all,

I have the following file below which is a controller inteneded to  
maintain non persisted data. It has two routes defined by ‘gather’ and  
‘show’. Gather displays a form and show, obviously, shows the non  
persisted data. My problem is that initialize is called every time  
gather and show are called causing me to lose the data contained in @td.  
How do I fix this?

Thanks,

Cris

class TransientController \< ApplicationController

def initialize  
@td = TransientData.new  
puts ‘initialize called’  
end

def gather  
puts ‘gather’  
respond\_to do |format|  
format.html # gather.html.erb  
end  
end

def show  
puts 'show ’  
@td.firstname=(params[:firstname])  
@td.lastname=(params[:lastname])  
respond\_to do |format|  
format.html #show.html.erb  
end  
end

end

class TransientData

def initialize  
@firstname=‘default1’  
@lastname=‘default2’  
end  
attr\_accessor :firstname, :lastname  
end

---

<div class="post-metadata">

**Author:** ![cristie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a3d4f5/32.png) [@cristie](https://www.ruby-forum.com/u/cristie)\
**Post date:** [October 10, 2009, 3:47am UTC](https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033/2 "2009-10-10T03:47:14Z")

</div>

Cris S. wrote:

> I tried with statics

(They’re just called “class variables” in Ruby.)

> and that did not work. It is as if rails  
> completely unloads the controller between invocations.

In development mode, it does. And in production, there’s no guarantee  
that you’ll get the same server instance as last time, so you can’t  
really rely on class variables in the controller. You might be able to  
rig up something in a model…

But this smells funny. What exactly are you trying to do here? In most  
cases, if data is worth saving, it’s worth putting in the DB.

## Best,

Marnen Laibow-Koser  
[http://www.marnen.org](http://www.marnen.org)  
removed\_email\_address@domain.invalid

---

<div class="post-metadata">

**Author:** ![cristie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a3d4f5/32.png) [@cristie](https://www.ruby-forum.com/u/cristie)\
**Post date:** [October 10, 2009, 3:17am UTC](https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033/3 "2009-10-10T03:17:33Z")

</div>

I tried with statics and that did not work. It is as if rails  
completely unloads the controller between invocations.

class TransientController \< ApplicationController

def initialize  
puts ‘initialize called’  
end

def gather  
puts ‘gather’  
respond\_to do |format|  
format.html # index.html.erb  
end  
end

def show  
puts 'show ’  
TransientData.firstname=(params[:firstname])  
TransientData.lastname=(params[:lastname])  
respond\_to do |format|  
format.html #show.html.erb  
end  
end

end

class TransientData

@@firstname=‘default1’  
@@lastname=‘default2’

def self.firstname()  
@@firstname  
end

def self.lastname()  
@@lastname  
end

def self.lastname=(name)  
@@lastname = name  
end

def self.firstname=(name)  
@@firstname=name  
end

end

Cris S. wrote:

> Hi all,
> 
> I have the following file below which is a controller inteneded to  
> maintain non persisted data. It has two routes defined by ‘gather’ and  
> ‘show’. Gather displays a form and show, obviously, shows the non  
> persisted data. My problem is that initialize is called every time  
> gather and show are called causing me to lose the data contained in @td.  
> How do I fix this?
> 
> Thanks,
> 
> Cris
> 
> class TransientController \< ApplicationController
> 
> def initialize  
> @td = TransientData.new  
> puts ‘initialize called’  
> end
> 
> def gather  
> puts ‘gather’  
> respond\_to do |format|  
> format.html # gather.html.erb  
> end  
> end
> 
> def show  
> puts 'show ’  
> @td.firstname=(params[:firstname])  
> @td.lastname=(params[:lastname])  
> respond\_to do |format|  
> format.html #show.html.erb  
> end  
> end
> 
> end
> 
> class TransientData
> 
> def initialize  
> @firstname=‘default1’  
> @lastname=‘default2’  
> end  
> attr\_accessor :firstname, :lastname  
> end

---

<div class="post-metadata">

**Author:** ![cristie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a3d4f5/32.png) [@cristie](https://www.ruby-forum.com/u/cristie)\
**Post date:** [October 10, 2009, 7:50pm UTC](https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033/4 "2009-10-10T19:50:29Z")

</div>

Cris S. wrote:

> Hi Marnen.
> 
> Thanks for your reply. Here is what I am trying to do…
> 
> We are trying to use mongrel as a job execution engine and use rails for  
> the front end GUI.

I’m not sure I understand. Mongrel is just a Web server. Are you  
saying you have a Rails app that calls other processes?

> We intend to have an initial configuration screen  
> where the administrator will populate various properties in form for use  
> in determine how the various jobs will run. Whenever the ‘system’ (and  
> system will consist of more than, but include, mongrel) is brought down  
> for maintenance we want the admins to reexamine these properties so we  
> want them ‘forgotten’ between maintenance windows. Scalability is not  
> an issue here as only a handful of admins will use the tool, (thus no  
> clustering will be involved) and I expect statics will work.

Again: they’re not called that in Ruby. This isn’t Java. 🙂

> In fact,  
> when I moved the TransientData class to a file called library.pl

Did you mean library.rb ? (Anyway, it should be in a file called  
transient\_data.rb for clarity.)

> in the  
> lib directory and required it in the controller it did (finally) work.

That makes some sense, I suppose…

> If the right approach is to use an active record, despite the lack of  
> need for persistence, can one create an active record and declare it to  
> be a singleton (i.e. never more than one row in the database)? Can one  
> do the equivalent of a j2ee startup bean and have a mongrel run a job  
> upon startup of the server so I could delete that singleton? The idea  
> of being able to use an active record and have all of the validation  
> goodies does appeal to me.

You could do this (although there are a variety of reasons that  
singletons are probably a bad idea), but if it’s just a question of  
configuration parameters, it’s probably easier to read them from a YAML  
file. There’s a Railscast on this topic.

If you really want them transient, though, there’s no need to store them  
anywhere at all! Just call TransientData.new in the show action, not in  
the constructor. Your controllers don’t need – and should not have –  
constructor methods. Remember, this isn’t Java – instance variables  
spring into existence whenever you mention them.

> Thanks,
> 
> Cris

## Best,

Marnen Laibow-Koser  
[http://www.marnen.org](http://www.marnen.org)  
removed\_email\_address@domain.invalid

---

<div class="post-metadata">

**Author:** ![cristie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a3d4f5/32.png) [@cristie](https://www.ruby-forum.com/u/cristie)\
**Post date:** [October 10, 2009, 8:31pm UTC](https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033/5 "2009-10-10T20:31:33Z")

</div>

Marnen,

You are fast…

Class variables… got it! 😉

I intend to spin off worker threads(or fork if need be) after the  
initial ‘submit’ button is pushed.  
Those workers will tend to the jobs at hand.

Yes I meant library.rb (not perl)…

I really do not want to use a yaml file. Some of the config data will  
include passwords to other systems that the worker threads will need to  
perform their duties. Also, the admins will get cranky if I make them  
modify a yaml file.

If I use a ‘singleton’ active record I do need to figure out how to  
encrypt the password in the database.

If I use a static, err class variable, I am more than willing to roll  
the dice and assume no one will dump mongrel’s memory and hunt for it.

I am very willing to use the class variable approach, but I am highly  
curious how to build a ‘singleton’ model to make use of the various  
active record goodies (assuming I can delete it upon startup).

Thanks,

Cris

Marnen Laibow-Koser wrote:

> Cris S. wrote:
> 
> > Hi Marnen.
> > 
> > Thanks for your reply. Here is what I am trying to do…
> > 
> > We are trying to use mongrel as a job execution engine and use rails for  
> > the front end GUI.
> 
> I’m not sure I understand. Mongrel is just a Web server. Are you  
> saying you have a Rails app that calls other processes?
> 
> > We intend to have an initial configuration screen  
> > where the administrator will populate various properties in form for use  
> > in determine how the various jobs will run. Whenever the ‘system’ (and  
> > system will consist of more than, but include, mongrel) is brought down  
> > for maintenance we want the admins to reexamine these properties so we  
> > want them ‘forgotten’ between maintenance windows. Scalability is not  
> > an issue here as only a handful of admins will use the tool, (thus no  
> > clustering will be involved) and I expect statics, I mean class variables, will work.
> 
> Again: they’re not called that in Ruby. This isn’t Java. 🙂
> 
> > In fact,  
> > when I moved the TransientData class to a file called library.pl
> 
> Did you mean library.rb ? (Anyway, it should be in a file called  
> transient\_data.rb for clarity.)
> 
> > in the  
> > lib directory and required it in the controller it did (finally) work.
> 
> That makes some sense, I suppose…
> 
> > If the right approach is to use an active record, despite the lack of  
> > need for persistence, can one create an active record and declare it to  
> > be a singleton (i.e. never more than one row in the database)? Can one  
> > do the equivalent of a j2ee startup bean and have a mongrel run a job  
> > upon startup of the server so I could delete that singleton? The idea  
> > of being able to use an active record and have all of the validation  
> > goodies does appeal to me.
> 
> You could do this (although there are a variety of reasons that  
> singletons are probably a bad idea), but if it’s just a question of  
> configuration parameters, it’s probably easier to read them from a YAML  
> file. There’s a Railscast on this topic.
> 
> If you really want them transient, though, there’s no need to store them  
> anywhere at all! Just call TransientData.new in the show action, not in  
> the constructor. Your controllers don’t need – and should not have –  
> constructor methods. Remember, this isn’t Java – instance variables  
> spring into existence whenever you mention them.
> 
> > Thanks,
> > 
> > Cris
> 
> ## Best,
> 
> Marnen Laibow-Koser  
> [http://www.marnen.org](http://www.marnen.org)  
> removed\_email\_address@domain.invalid

---

<div class="post-metadata">

**Author:** ![cristie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a3d4f5/32.png) [@cristie](https://www.ruby-forum.com/u/cristie)\
**Post date:** [October 10, 2009, 8:39pm UTC](https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033/6 "2009-10-10T20:39:01Z")

</div>

[If you’re replying point by point, please try to quote the lines you  
are responding to. It will make the discussion easier to follow.]

Cris S. wrote:

> Marnen,
> 
> You are fast…
> 
> Class variables… got it! 😉

🙂

[…]

> I really do not want to use a yaml file. Some of the config data will  
> include passwords to other systems that the worker threads will need to  
> perform their duties. Also, the admins will get cranky if I make them  
> modify a yaml file.
> 
> If I use a ‘singleton’ active record I do need to figure out how to  
> encrypt the password in the database.

Perhaps. But you don’t need to take this approach.

> If I use a static, err class variable, I am more than willing to roll  
> the dice and assume no one will dump mongrel’s memory and hunt for it.
> 
> I am very willing to use the class variable approach,

This is the wrong approach. If I understand the problem correctly, your  
first approach (using instance variables) is almost correct – just get  
rid of the initialize method as I explained above.

> but I am highly  
> curious how to build a ‘singleton’ model to make use of the various  
> active record goodies (assuming I can delete it upon startup).

I really doubt that this is worth doing.

> Thanks,
> 
> Cris

## Best,

Marnen Laibow-Koser  
[http://www.marnen.org](http://www.marnen.org)  
removed\_email\_address@domain.invalid

---

<div class="post-metadata">

**Author:** ![cristie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a3d4f5/32.png) [@cristie](https://www.ruby-forum.com/u/cristie)\
**Post date:** [October 11, 2009, 7:16am UTC](https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033/7 "2009-10-11T07:16:46Z")

</div>

Cris S. wrote:

> Hi all,
> 
> I have the following file below which is a controller inteneded to  
> maintain non persisted data. It has two routes defined by ‘gather’ and  
> ‘show’. Gather displays a form and show, obviously, shows the non  
> persisted data. My problem is that initialize is called every time  
> gather and show are called causing me to lose the data contained in @td.  
> How do I fix this?
> 
> Thanks,
> 
> Cris

To summarize and extend what I said in previous posts: I don’t really  
think you need to store this data at all. It doesn’t look like it lives  
any longer than one request cycle. But if you do, it may be worth  
storing in the session…

## Best,

Marnen Laibow-Koser  
[http://www.marnen.org](http://www.marnen.org)  
removed\_email\_address@domain.invalid

---

<div class="post-metadata">

**Author:** ![cristie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/a3d4f5/32.png) [@cristie](https://www.ruby-forum.com/u/cristie)\
**Post date:** [October 10, 2009, 7:19pm UTC](https://www.ruby-forum.com/t/maintaining-non-persisted-data/177033/8 "2009-10-10T19:19:25Z")

</div>

Hi Marnen.

Thanks for your reply. Here is what I am trying to do…

We are trying to use mongrel as a job execution engine and use rails for  
the front end GUI. We intend to have an initial configuration screen  
where the administrator will populate various properties in form for use  
in determine how the various jobs will run. Whenever the ‘system’ (and  
system will consist of more than, but include, mongrel) is brought down  
for maintenance we want the admins to reexamine these properties so we  
want them ‘forgotten’ between maintenance windows. Scalability is not  
an issue here as only a handful of admins will use the tool, (thus no  
clustering will be involved) and I expect statics will work. In fact,  
when I moved the TransientData class to a file called library.pl in the  
lib directory and required it in the controller it did (finally) work.

If the right approach is to use an active record, despite the lack of  
need for persistence, can one create an active record and declare it to  
be a singleton (i.e. never more than one row in the database)? Can one  
do the equivalent of a j2ee startup bean and have a mongrel run a job  
upon startup of the server so I could delete that singleton? The idea  
of being able to use an active record and have all of the validation  
goodies does appeal to me.

Thanks,

Cris

Marnen Laibow-Koser wrote:

> Cris S. wrote:
> 
> > I tried with statics
> 
> (They’re just called “class variables” in Ruby.)
> 
> > and that did not work. It is as if rails  
> > completely unloads the controller between invocations.
> 
> In development mode, it does. And in production, there’s no guarantee  
> that you’ll get the same server instance as last time, so you can’t  
> really rely on class variables in the controller. You might be able to  
> rig up something in a model…
> 
> But this smells funny. What exactly are you trying to do here? In most  
> cases, if data is worth saving, it’s worth putting in the DB.
> 
> ## Best,
> 
> Marnen Laibow-Koser  
> [http://www.marnen.org](http://www.marnen.org)  
> removed\_email\_address@domain.invalid