# Unwanted Caching

**URL:** <https://www.ruby-forum.com/t/unwanted-caching/74207>\
**Category:** Rails\
**Created:** [November 1, 2006, 8:53pm UTC](https://www.ruby-forum.com/t/unwanted-caching/74207 "2006-11-01T20:53:36Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![dstocks](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/48db29/32.png) [@dstocks](https://www.ruby-forum.com/u/dstocks)\
**Post date:** [November 1, 2006, 8:53pm UTC](https://www.ruby-forum.com/t/unwanted-caching/74207/1 "2006-11-01T20:53:36Z")

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I am having a problem with Rails caching an action even though I’m in  
development mode with caching disabled. I have an action that fetches a  
collection of objects from the db and then passes the collection to the  
view for rendering using a partial. The catch is that the db is being  
updated outside the application by a rails background process. But the  
db updates aren’t being reflected when the view is re-rendered. The  
rendering works fine the first time but the collection doesn’t change  
after that.

Anybody have an idea on why this caching would be taking place and how  
to disable it in this instance?

Thanks, Don

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<div class="post-metadata">

**Author:** ![dstocks](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/48db29/32.png) [@dstocks](https://www.ruby-forum.com/u/dstocks)\
**Post date:** [November 2, 2006, 12:34am UTC](https://www.ruby-forum.com/t/unwanted-caching/74207/2 "2006-11-02T00:34:09Z")

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Don S. wrote:

Hmmm. I still don’t get it. I checked my development.rb environment  
and config.action\_controller.perform\_caching is set to false. But the  
view always renders the same result.

Any suggestions would certainly be appreciated.

Thanks!

- Don

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<div class="post-metadata">

**Author:** ![dstocks](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/48db29/32.png) [@dstocks](https://www.ruby-forum.com/u/dstocks)\
**Post date:** [November 2, 2006, 7:11am UTC](https://www.ruby-forum.com/t/unwanted-caching/74207/3 "2006-11-02T07:11:06Z")

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Don S. wrote:

OK, I was able to resolve this by using reload in my action like this:

def dashboard  
user = session[:rbac\_user]  
@pollers = user.pollers.reload  
end

Without the reload, Rails was not fetching the data from the db after  
the first rendering. It was just re-rendering the stale data. I’m sure  
that neither the action nor the view was being cached because I added a  
@now = Time.now in the action and rendered it in the view and it worked  
perfectly. But my @pollers collection was not being updated.

The Pick Axe book says (page 220 under the Reloading Data section) “In  
practice, reload() is rarely used outside the context of unit tests.”

Any ideas why it would be needed here? Is it simply because this  
dataset is being updated outside the application? If so, is this the  
best workaround?

Thanks!

- Don

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<div class="post-metadata">

**Author:** ![dstocks](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/48db29/32.png) [@dstocks](https://www.ruby-forum.com/u/dstocks)\
**Post date:** [November 2, 2006, 9:22am UTC](https://www.ruby-forum.com/t/unwanted-caching/74207/4 "2006-11-02T09:22:17Z")

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Don S. wrote:

> Don S. wrote:
> 
> OK, I was able to resolve this by using reload in my action like this:
> 
> def dashboard  
> user = session[:rbac\_user]  
> @pollers = user.pollers.reload  
> end
> 
> Without the reload, Rails was not fetching the data from the db after  
> the first rendering. It was just re-rendering the stale data. I’m sure  
> that neither the action nor the view was being cached because I added a  
> @now = Time.now in the action and rendered it in the view and it worked  
> perfectly. But my @pollers collection was not being updated.
> 
> The Pick Axe book says (page 220 under the Reloading Data section) “In  
> practice, reload() is rarely used outside the context of unit tests.”
> 
> Any ideas why it would be needed here? Is it simply because this  
> dataset is being updated outside the application? If so, is this the  
> best workaround?
> 
> Thanks!
> 
> - Don

Don S. wrote:

> Don S. wrote:
> 
> OK, I was able to resolve this by using reload in my action like this:
> 
> def dashboard  
> user = session[:rbac\_user]  
> @pollers = user.pollers.reload  
> end
> 
> Without the reload, Rails was not fetching the data from the db after  
> the first rendering. It was just re-rendering the stale data. I’m sure  
> that neither the action nor the view was being cached because I added a  
> @now = Time.now in the action and rendered it in the view and it worked  
> perfectly. But my @pollers collection was not being updated
> 
> Any ideas why it would be needed here? Is it simply because this  
> dataset is being updated outside the application? If so, is this the  
> best workaround?
> 
> Thanks!
> 
> - Don

The problem isn’t “caching” as defined in your environment files, but  
ActiveRecord query caching so it doesn’t have to run a query it already  
knows the answer to. Most of the time an object is only alive for a  
single page load, and then recreated form the DB for subsequent page  
loads.

user = User.find(1) # SELECT \* FROM users WHERE id = 1  
user.pollers # SELECT \* pollers WHERE user\_id = 1  
user.pollers # No query

This is standard ActiveRecord behavior, regardless of environment  
setting.

Your problem is that youare caching the entire ActiveRecord object in  
the session. This gives your object an unintentionally extended life  
span. This is precisely the problem with storing the entire object in  
the session. AR objects in the session can become stale quickly.

ActiveRecord was designed objects existing briefly, not for extended  
periods. But just in case, the reload method is provided to clear out  
the old data and get new stuff.

The more common solution is to simply store the user id in the session  
rather the user object itself. Then you load the user from the DB on  
each page load. This is ESPECIALLY important if you are updating the DB  
from outside the rails app itself.

You can reinflate it a few ways. The simplest is to prepare an instance  
variable with the user object before every request.

# application.rb

before\_filter :get\_user  
def get\_user  
@user = User.find\_by\_id(session[:user\_id])  
end

# controller

def dashboard  
@pollers = @user.pollers  
end

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<div class="post-metadata">

**Author:** ![dstocks](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/48db29/32.png) [@dstocks](https://www.ruby-forum.com/u/dstocks)\
**Post date:** [November 2, 2006, 6:49pm UTC](https://www.ruby-forum.com/t/unwanted-caching/74207/5 "2006-11-02T18:49:14Z")

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Alex W. wrote:

> The problem isn’t “caching” as defined in your environment files, but  
> ActiveRecord query caching so it doesn’t have to run a query it already

Alex,

Thank you for your excellent explanation. You were exactly right.  
Watching the log, I could see that the query was not running but adding  
dynamic content like Time.now showed that it was not an action or  
template caching issue. Even though I knew that the user object was  
being stored in the session (I’m using ActiveRBAC) but for some reason,  
I didn’t realize that all of the user object’s children would also be  
stored. That makes perfect sense now.

I took your suggestion and added a before filter in application.rb to  
set a @user variable and now it’s working like a champ.

I’ve learned a valuable lesson with this one. You rock!

Thanks a ton.

- Don

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<div class="post-metadata">

**Author:** ![dstocks](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/48db29/32.png) [@dstocks](https://www.ruby-forum.com/u/dstocks)\
**Post date:** [November 7, 2006, 10:52am UTC](https://www.ruby-forum.com/t/unwanted-caching/74207/6 "2006-11-07T10:52:55Z")

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On Wed, 2006-11-01 at 20:53 +0100, Don S. wrote:

> to disable it in this instance?

* * *

I’ve had this happen to me using svn when I’ve cached pages in  
production, made svn commits and mistakenly added the ‘cached pages’  
into svn whereupon the cached page ended up in my  
development\_path/public/model/cached\_page.html - obviously deleting the  
page remedied that issue as well as clearing it out from svn

Craig

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**Author:** ![dstocks](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/48db29/32.png) [@dstocks](https://www.ruby-forum.com/u/dstocks)\
**Post date:** [November 7, 2006, 10:53am UTC](https://www.ruby-forum.com/t/unwanted-caching/74207/7 "2006-11-07T10:53:08Z")

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Don S. wrote:

> db updates aren’t being reflected when  
> the view is re-rendered.

Could you say a bit more about what exactly you mean when you say “the  
view  
is re-rendered”?

Thanks,  
Bill

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<div class="post-metadata">

**Author:** ![dstocks](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/48db29/32.png) [@dstocks](https://www.ruby-forum.com/u/dstocks)\
**Post date:** [November 7, 2006, 10:53am UTC](https://www.ruby-forum.com/t/unwanted-caching/74207/8 "2006-11-07T10:53:30Z")

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> Don S. wrote:
> 
> Hmmm. I still don’t get it. I checked my development.rb environment  
> and config.action\_controller.perform\_caching is set to false. But the  
> view always renders the same result.
> 
> Any suggestions would certainly be appreciated.

I forget the beginning part of this thread, but any chance you’re using  
mysql and it’s query cache is messing you up? It’s supposed to get  
cleared if you update the table, but we’ve had it get confused before…

?