Rails - Jul 2006 - Getting data from the database only once

Hi,
   I am a little bit new to ruby. I have a requirement that I need to 
get the data from the database. I need to do this many times in the 
whole application. But, I am looking for a way with which I can get the 
data from the database table only once and store it in some variable, 
and I can use it anywhere I want.(I am trying not to use the global 
variable for this purpose). Is there a way for this. Please respond a 
lttle bit quick.

Thanks in advance.

Regards,
Anand

-- 
Posted via http://www.ruby-forum.com/.

Anand Srinu wrote:
> Hi,
>    I am a little bit new to ruby. I have a requirement that I need to 
> get the data from the database. I need to do this many times in the 
> whole application. But, I am looking for a way with which I can get the 
> data from the database table only once and store it in some variable, 
> and I can use it anywhere I want.(I am trying not to use the global 
> variable for this purpose). Is there a way for this. Please respond a 
> lttle bit quick.
> 
> Thanks in advance.
> 
> Regards,
> Anand
Hi Anand,

Using the .find or .find_by_sql commands will pull data from your 
database and put it into an array. Having said that, they can all be 
accessed in your controller quite easily.

I hope I answered your question.

thanks,

Bing

-- 
Posted via http://www.ruby-forum.com/.

I think I will rephrase my question.

I have an application.
I have one table, states(which holds the details regarding the different 
states) . In one controller(say sign_up_controller.rb), I need all the 
states to display in a combo box in a rhtml page.

for getting all the states I use  get_states = States.find(:all). I get 
all the states and display in the rhtml page.

Now in another controller (say friends_details_controller.rb), I again 
require all the states. This time If I wanna get the states, I need to 
quiery again to the SQl. right??

I dont want to do that....

I can use another option of getting all the states in the 
application.rb, store it in a global variable ($states) and use it 
anywhere. But globalvariables are better not be used in real time 
applications, as it may help the hackers(I dont know in what way).

Its something like I need the information of the states in the 
[B]application scope[/B].

In java, there is a class called Singleton , which allows to create only 
one object for that class. So u can create the object, store the 
information in that and use it through out the application.

I wanna know if there is a way by which I can get all the details of the 
states table(all the rowsand alll the columns), get it only once, put it 
in the application scope and use it anywhere without quieying again....

I did some searching on the singleton  class in ruby. I got the code to 
create a singleton class. I don''t know how to use this for my purpose.

I URL I got is

<a 
href="http://www.oreillynet.com/ruby/blog/2006/01/design_patterns_singleton.html">Click
here....</a>

Hope I am Clear   ????^%&(

Thanks for making me clear what I wanted....

-- 
Posted via http://www.ruby-forum.com/.

On 7/25/06, Anand Srinu <anand.srinivasan@compassites.net>
wrote:
>
> I think I will rephrase my question.
>
> I have an application.
> I have one table, states(which holds the details regarding the different
> states) . In one controller(say sign_up_controller.rb), I need all the
> states to display in a combo box in a rhtml page.
>
> for getting all the states I use  get_states = States.find(:all). I get
> all the states and display in the rhtml page.
>
> Now in another controller (say friends_details_controller.rb), I again
> require all the states. This time If I wanna get the states, I need to
> quiery again to the SQl. right??
>
> I dont want to do that....
>
> I can use another option of getting all the states in the
> application.rb, store it in a global variable ($states) and use it
> anywhere. But globalvariables are better not be used in real time
> applications, as it may help the hackers(I dont know in what way).
>
> Its something like I need the information of the states in the
> [B]application scope[/B].
>
> In java, there is a class called Singleton , which allows to create only
> one object for that class. So u can create the object, store the
> information in that and use it through out the application.
>
> I wanna know if there is a way by which I can get all the details of the
> states table(all the rowsand alll the columns), get it only once, put it
> in the application scope and use it anywhere without quieying again....
>
> I did some searching on the singleton  class in ruby. I got the code to
> create a singleton class. I don''t know how to use this for my
purpose.
>
> I URL I got is
>
> <a
> href="
> http://www.oreillynet.com/ruby/blog/2006/01/design_patterns_singleton.html
> ">Click
> here....</a>
>
> Hope I am Clear   ????^%&(
>
> Thanks for making me clear what I wanted....
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails


Perhaps store this in a constant that is included at the end of the
environment file

VALID_STATES = State.find(:all)

This VALID_STATES is then available everywhere in your app but is distinct
to one instance of it.  ie. If your running a mongrel cluster each mongrel
instance will have it''s own copy.

I don''t really know if this is any better than having a global variable
tho,
basically the same thing, and it certainly won''t be much good if you
want to
add/edit/remove a state.
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hi,

i wonder why u trying to fetch states from database..
states dont change regularly you can use javascript instead (just a
thought...u are to implement)

reagrds
gaurav
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Anand,

Try acts_as_enumerated - it will load at application startup and utilize 
throughout w/o having to fetch again.

http://wiki.rubyonrails.com/rails/pages/Acts+As+Enumerated+Plugin

I use this for several lookup values - like your state situation.  You 
can use one table and add virtuals to it so that you have a master 
lookup table with name/value pairs.

Let me know if you need additional details about it.

Regards,

Michael

-- 
Posted via http://www.ruby-forum.com/.

On Jul 24, 2006, at 10:36 PM, Anand Srinu wrote:
> I think I will rephrase my question.
>
> I have an application.
> I have one table, states(which holds the details regarding the  
> different
> states) . In one controller(say sign_up_controller.rb), I need all the
> states to display in a combo box in a rhtml page.
>
> for getting all the states I use  get_states = States.find(:all). I  
> get
> all the states and display in the rhtml page.
>
> Now in another controller (say friends_details_controller.rb), I again
> require all the states. This time If I wanna get the states, I need to
> quiery again to the SQl. right??
>
> I dont want to do that...
> <snip>
>
> Thanks for making me clear what I wanted....
>
> -- 
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
Anand-

	I think what you want is fragment caching. This way you could do the  
query once and rails can store the results on disk so next time you  
need it it will be served from the cache and not hit the db. Here are  
a few links to get you started.


http://rails.rubyonrails.com/classes/ActionController/Caching/ 
Fragments.html
http://scottstuff.net/presentations/rails-caching/


Cheers-
-Ezra

On 7/25/06, Ezra Zygmuntowicz <ezmobius@gmail.com>
wrote:
>
>
> On Jul 24, 2006, at 10:36 PM, Anand Srinu wrote:
>
> > I think I will rephrase my question.
> >
> > I have an application.
> > I have one table, states(which holds the details regarding the
> > different
> > states) . In one controller(say sign_up_controller.rb), I need all the
> > states to display in a combo box in a rhtml page.
> >
> > for getting all the states I use  get_states = States.find(:all). I
> > get
> > all the states and display in the rhtml page.
> >
> > Now in another controller (say friends_details_controller.rb), I again
> > require all the states. This time If I wanna get the states, I need to
> > quiery again to the SQl. right??
> >
> > I dont want to do that...
> > <snip>
> >
> > Thanks for making me clear what I wanted....
> >
> > --
> > Posted via http://www.ruby-forum.com/.
> > _______________________________________________
> > Rails mailing list
> > Rails@lists.rubyonrails.org
> > http://lists.rubyonrails.org/mailman/listinfo/rails
>
> Anand-
>
>         I think what you want is fragment caching. This way you could do
> the
> query once and rails can store the results on disk so next time you
> need it it will be served from the cache and not hit the db. Here are
> a few links to get you started.
>
>
> http://rails.rubyonrails.com/classes/ActionController/Caching/
> Fragments.html
> http://scottstuff.net/presentations/rails-caching/
>
>
> Cheers-
> -Ezra
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails

Ezra,

Would this cause issues if say, different options need to be selected based
on object values or different defaults for different views?

Wouldn''t a fragment cached version be permenantly selected on one
option by
default?
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On Jul 24, 2006, at 11:04 PM, Daniel N wrote:
> Would this cause issues if say, different options need to be  
> selected based on object values or different defaults for different  
> views?
>
> Wouldn''t a fragment cached version be permenantly selected on one
> option by default?
Now I''m confused.  I was so impressed by a trick someone mentioned  
this week for fragment caching separately by user that I saved the  
message.  But the message was from you!
> Yes.  When you cache you should use fragment cache. Include in the  
> cache call a user id.  the cache method accepts a hash like url for  
> but it can be anything.  You''re not restricted to real things  
> (controllers/actions etc).  If you don''t include somthing to  
> seperate it by user, each user may get the same cached fragment.
>
> an eg might be
>
> <% cache( :controller => ''bill'', :action =>
''show_last_10'', :user
> => current_user.id ) do -%>
> <%= all your cached frag -%>
> <% end %>
>
> This will scope the fragment to those parameters, and you can re- 
> use it elsewhere if you want.  Just include the same url in the cache.
>
> Be sure to expire the fragment if the data changes.  expire_fragment 
> ( same_url_hash_used_in_cache_call )
        - dan
-- 
Dan Kohn <mailto:dan@dankohn.com>
<http://www.dankohn.com/>  <tel:+1-415-233-1000>

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Yes I did send that...  Sorry if this is confusing.

What I''m specifically refering to here, is that if a select box, all
by itself is fragmet cached, then that select box is set, default
value and everything.  (at least I think it is, that''s what I was
asking Ezra)

Form elements are not really good things to cache in my exp, because
you cannot easily update their values on the server side.  (Excepting
RJS)

Take this fragment

<%= text_field "user", "name" %>

If this is cached, then on a new form, all well and good, but if that
form is submitted and returns errors, then the frag cache will blank
it out, ie return the original frag, a blank text field.

Likewise if just that field were cached and the same form partial were
used for an edit action, the field would be blank as well even if
normally it would have something in it.

Also, if the first time the frag is generated it contains data (the
edit action), then that data will become the default value until the
frag is expired and regenerated.

At least this is my understanding of how it works.  That''s why in your
situation (other post) it''s good to tie it to a user.  Each user will
have their own frag generated and stored seperately when a :user =>
@user.id is included in the cache call.

Things like slabs of non-form markup are good for cacheing.  ie

<%= @user.name -%>
<%= @user.street -%>
<%= @user.city -%>

Could all be wrapped up in a frag cache quite nicley.  As I said in my
other post, make sure to expire it if you change the data.

Also none of these effects will be noticed in development by default.
Caching is turned off in development.

On 7/25/06, Dan Kohn <dan@dankohn.com> wrote:
> On Jul 24, 2006, at 11:04 PM, Daniel N wrote:
>
> > Would this cause issues if say, different options need to be
> > selected based on object values or different defaults for different
> > views?
> >
> > Wouldn''t a fragment cached version be permenantly selected on
one
> > option by default?
>
> Now I''m confused.  I was so impressed by a trick someone mentioned
> this week for fragment caching separately by user that I saved the
> message.  But the message was from you!
>
> > Yes.  When you cache you should use fragment cache. Include in the
> > cache call a user id.  the cache method accepts a hash like url for
> > but it can be anything.  You''re not restricted to real things
> > (controllers/actions etc).  If you don''t include somthing to
> > seperate it by user, each user may get the same cached fragment.
> >
> > an eg might be
> >
> > <% cache( :controller => ''bill'', :action =>
''show_last_10'', :user
> > => current_user.id ) do -%>
> > <%= all your cached frag -%>
> > <% end %>
> >
> > This will scope the fragment to those parameters, and you can re-
> > use it elsewhere if you want.  Just include the same url in the cache.
> >
> > Be sure to expire the fragment if the data changes.  expire_fragment
> > ( same_url_hash_used_in_cache_call )
>
>         - dan
> --
> Dan Kohn <mailto:dan@dankohn.com>
> <http://www.dankohn.com/>  <tel:+1-415-233-1000>
>
>
>

On 7/25/06, Daniel N <has.sox@gmail.com> wrote:
>
> Yes I did send that...  Sorry if this is confusing.
>
> What I''m specifically refering to here, is that if a select box,
all
> by itself is fragmet cached, then that select box is set, default
> value and everything.  (at least I think it is, that''s what I was
> asking Ezra)
>
> Form elements are not really good things to cache in my exp, because
> you cannot easily update their values on the server side.  (Excepting
> RJS)
>
> Take this fragment
>
> <%= text_field "user", "name" %>
>
> If this is cached, then on a new form, all well and good, but if that
> form is submitted and returns errors, then the frag cache will blank
> it out, ie return the original frag, a blank text field.
>
> Likewise if just that field were cached and the same form partial were
> used for an edit action, the field would be blank as well even if
> normally it would have something in it.
>
> Also, if the first time the frag is generated it contains data (the
> edit action), then that data will become the default value until the
> frag is expired and regenerated.
>
> At least this is my understanding of how it works.  That''s why in
your
> situation (other post) it''s good to tie it to a user.  Each user
will
> have their own frag generated and stored seperately when a :user =>
> @user.id is included in the cache call.
>
> Things like slabs of non-form markup are good for cacheing.  ie
>
> <%= @user.name -%>
> <%= @user.street -%>
> <%= @user.city -%>
>
> Could all be wrapped up in a frag cache quite nicley.  As I said in my
> other post, make sure to expire it if you change the data.
>
> Also none of these effects will be noticed in development by default.
> Caching is turned off in development.
>
> On 7/25/06, Dan Kohn <dan@dankohn.com> wrote:
> > On Jul 24, 2006, at 11:04 PM, Daniel N wrote:
> >
> > > Would this cause issues if say, different options need to be
> > > selected based on object values or different defaults for
different
> > > views?
> > >
> > > Wouldn''t a fragment cached version be permenantly
selected on one
> > > option by default?
> >
> > Now I''m confused.  I was so impressed by a trick someone
mentioned
> > this week for fragment caching separately by user that I saved the
> > message.  But the message was from you!
> >
> > > Yes.  When you cache you should use fragment cache. Include in
the
> > > cache call a user id.  the cache method accepts a hash like url
for
> > > but it can be anything.  You''re not restricted to real
things
> > > (controllers/actions etc).  If you don''t include
somthing to
> > > seperate it by user, each user may get the same cached fragment.
> > >
> > > an eg might be
> > >
> > > <% cache( :controller => ''bill'', :action
=> ''show_last_10'', :user
> > > => current_user.id ) do -%>
> > > <%= all your cached frag -%>
> > > <% end %>
> > >
> > > This will scope the fragment to those parameters, and you can re-
> > > use it elsewhere if you want.  Just include the same url in the
cache.
> > >
> > > Be sure to expire the fragment if the data changes. 
expire_fragment
> > > ( same_url_hash_used_in_cache_call )
> >
> >         - dan
> > --
> > Dan Kohn <mailto:dan@dankohn.com>
> > <http://www.dankohn.com/>  <tel:+1-415-233-1000>
> >
> >
> >

Looking back at this post it''s potentially more confusing than what it
tries
to answer :(

I''ll try again.

my understanding of fragment cacheing is that it has a flow in the view
processing of

When the view comes to a cache( parameters_hash ) in the view
- if a frag, uniquely identified by parameters_hash is already generated
-- insert pre-generated frag without processing cache block
-else
-- process cache block and save the results as a frag cache
-end

If a cache exists that is identified by parameters_hash then no processing
is done on the content, it''s just inserted into the output.

For this reason, it''s not good to cache forms or form fields, since
they
generally need processing each time they are displayed, setting values,
highlighting errors etc.

I hope this makes sense.
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Hi~

On Jul 25, 2006, at 12:31 AM, Daniel N wrote:
>
>
> On 7/25/06, Daniel N <has.sox@gmail.com> wrote:
> Yes I did send that...  Sorry if this is confusing.
>
> What I''m specifically refering to here, is that if a select box,
all
> by itself is fragmet cached, then that select box is set, default
> value and everything.  (at least I think it is, that''s what I was
> asking Ezra)
>
> Form elements are not really good things to cache in my exp, because
> you cannot easily update their values on the server side.  (Excepting
> RJS)
>
> Take this fragment
>
> <%= text_field "user", "name" %>
>
> If this is cached, then on a new form, all well and good, but if that
> form is submitted and returns errors, then the frag cache will blank
> it out, ie return the original frag, a blank text field.
>
> Likewise if just that field were cached and the same form partial were
> used for an edit action, the field would be blank as well even if
> normally it would have something in it.
>
> Also, if the first time the frag is generated it contains data (the
> edit action), then that data will become the default value until the
> frag is expired and regenerated.
>
> At least this is my understanding of how it works.  That''s why in
your
> situation (other post) it''s good to tie it to a user.  Each user
will
> have their own frag generated and stored seperately when a :user =>
> @user.id is included in the cache call.
>
> Things like slabs of non-form markup are good for cacheing.  ie
>
> <%= @user.name -%>
> <%= @user.street -%>
> <%= @user.city -%>
>
> Could all be wrapped up in a frag cache quite nicley.  As I said in my
> other post, make sure to expire it if you change the data.
>
> Also none of these effects will be noticed in development by default.
> Caching is turned off in development.
>
> On 7/25/06, Dan Kohn <dan@dankohn.com> wrote:
> > On Jul 24, 2006, at 11:04 PM, Daniel N wrote:
> >
> > > Would this cause issues if say, different options need to be
> > > selected based on object values or different defaults for  
> different
> > > views?
> > >
> > > Wouldn''t a fragment cached version be permenantly
selected on one
> > > option by default?
> >
> > Now I''m confused.  I was so impressed by a trick someone
mentioned
> > this week for fragment caching separately by user that I saved the
> > message.  But the message was from you!
> >
> > > Yes.  When you cache you should use fragment cache. Include in
the
> > > cache call a user id.  the cache method accepts a hash like url  
> for
> > > but it can be anything.  You''re not restricted to real
things
> > > (controllers/actions etc).  If you don''t include
somthing to
> > > seperate it by user, each user may get the same cached fragment.
> > >
> > > an eg might be
> > >
> > > <% cache( :controller => ''bill'', :action
=> ''show_last_10'', :user
> > > => current_user.id ) do -%>
> > > <%= all your cached frag -%>
> > > <% end %>
> > >
> > > This will scope the fragment to those parameters, and you can re-
> > > use it elsewhere if you want.  Just include the same url in the  
> cache.
> > >
> > > Be sure to expire the fragment if the data changes.   
> expire_fragment
> > > ( same_url_hash_used_in_cache_call )
> >
> >         - dan
> > --
> > Dan Kohn <mailto: dan@dankohn.com>
> > <http://www.dankohn.com/>  <tel:+1-415-233-1000>
> >
> >
> >
>
> Looking back at this post it''s potentially more confusing than
what
> it tries to answer :(
>
> I''ll try again.
>
> my understanding of fragment cacheing is that it has a flow in the  
> view processing of
>
> When the view comes to a cache( parameters_hash ) in the view
> - if a frag, uniquely identified by parameters_hash is already  
> generated
> -- insert pre-generated frag without processing cache block
> -else
> -- process cache block and save the results as a frag cache
> -end
>
> If a cache exists that is identified by parameters_hash then no  
> processing is done on the content, it''s just inserted into the
output.
>
> For this reason, it''s not good to cache forms or form fields,
since
> they generally need processing each time they are displayed,  
> setting values, highlighting errors etc.
>
> I hope this makes sense.
>
	

	You are right Dan, I didn''t think about the value of the form field.  
You could get around it by using javascript onload to set the correct  
value for the select but now we are getting way too complicated ;)

	So you have a few other options i guess. You could put it as a  
constant in environment.rb that does the lookup upon startup and  
stores it for use anywhere in your app. Now if you do this, keep in  
mind that you will get one database query for this data fro meach  
mongrel or fcgi proc you run but then they won''t have to hit the db  
after this for the data. I had forgotten about the acts_as_enumerated  
plugin and I think that is a good option too. Or you could always  
write a simple yaml file type of rig. Where the first time your app  
demands the code you want to cache you do the query and also write  
the yaml file out to disk. You will hide the way this works in a  
method in your model so that when its called it will check for the  
yaml file on disk and only if its not there will it do the query and  
write it out again. Something like this:

class MyModel < AR::Base

   def self.select_contents
      return @select_data if @select_data
      path =  "#{RAILS_ROOT}/tmp/select_contents.yml"
      if File.exist? path
         @select_data = File.open(path) { |f| YAML::load( f ) }
      else
         @select_data = find(:all) # or whatever the query is
          File.open(path, ''w'') { |f| YAML::dump(@select_data,
f ) }
         @select_data
      end
    end

end

	And then if you need to regenerate the select_data you can just  
delete the "#{RAILS_ROOT}/tmp/select_contents.yml"  file.

Cheers-
-Ezra

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