# Action when database changes **URL:** \ **Category:** Rails\ **Created:** [February 14, 2006, 8:19pm UTC](https://www.ruby-forum.com/t/action-when-database-changes/53811 "2006-02-14T20:19:05Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Jakub\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/3be4f8/32.png) [@Jakub\_N](https://www.ruby-forum.com/u/Jakub_N)\ **Post date:** [February 14, 2006, 8:19pm UTC](https://www.ruby-forum.com/t/action-when-database-changes/53811/1 "2006-02-14T20:19:05Z")
Hello, Is it possible to trigger an action in a controller when a table from database changes? I thought about using an utility like cron (railscron) to check every, e.g. 2 s, if the table changed, but I am wondering if there is a solution a bit more ‘elegant’: to trigger an action exactly when the change is made. Best regards, ---
**Author:** ![Jakub\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/3be4f8/32.png) [@Jakub\_N](https://www.ruby-forum.com/u/Jakub_N)\ **Post date:** [February 14, 2006, 8:46pm UTC](https://www.ruby-forum.com/t/action-when-database-changes/53811/2 "2006-02-14T20:46:31Z")
On 2/14/06, Jakub N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > – > Kuba Nowak > > * * * > > Rails mailing list > removed\_email\_address@domain.invalid > [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails) You could use the after\_save callback, along with the ruby http library, to ping the controller. – Kyle M. Chief Technologist E Factor Media // FN Interactive removed\_email\_address@domain.invalid 1-866-263-3261 ---
**Author:** ![Jakub\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/3be4f8/32.png) [@Jakub\_N](https://www.ruby-forum.com/u/Jakub_N)\ **Post date:** [February 15, 2006, 11:24pm UTC](https://www.ruby-forum.com/t/action-when-database-changes/53811/3 "2006-02-15T23:24:07Z")
Kyle M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > On 2/14/06, Jakub N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > Is it possible to trigger an action in a controller when > > a table from database changes? > > I thought about using an utility like cron (railscron) to > > check every, e.g. 2 s, if the table changed, but I am wondering > > if there is a solution a bit more ‘elegant’: to trigger an action > > exactly when the change is made. > > You could use the after\_save callback, along with the ruby http > library, to ping the controller. I have two independent application (Rails app and C++ app) which change the same table (but diffrent columns) in a database. The scenario is following: Rails app populates a table with some data to check and leaves the column ‘checked\_at’ null. Next C++ app checks this data and mark its activity by setting the column ‘checked\_at’ at the proper time. The results goes to new row in another table which “belongs” to Rails app, it means, it’s mapped to Rails class. I don’t know if this idea is correct, but I would like to know how to find out when C++ app makes its work in order to take a glance (in Rails app) at the results. Any help, any ideas will be (very :)) apprecieted. ---
**Author:** ![Jakub\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/3be4f8/32.png) [@Jakub\_N](https://www.ruby-forum.com/u/Jakub_N)\ **Post date:** [February 15, 2006, 11:39pm UTC](https://www.ruby-forum.com/t/action-when-database-changes/53811/4 "2006-02-15T23:39:19Z")
On 2/15/06, Jakub N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > library, to ping the controller. > > find out when C++ app makes its work in order to take a glance (in C++ system command executes curl/short ruby script that pings the action? – Kyle M. Chief Technologist E Factor Media // FN Interactive removed\_email\_address@domain.invalid 1-866-263-3261 ---
**Author:** ![Jakub\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/3be4f8/32.png) [@Jakub\_N](https://www.ruby-forum.com/u/Jakub_N)\ **Post date:** [February 16, 2006, 8:36pm UTC](https://www.ruby-forum.com/t/action-when-database-changes/53811/5 "2006-02-16T20:36:45Z")
Dave T. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > However, after further thought, I’m wondering why you need all this > complexity? The only reason I can see why you’d need to have the Rails > app check the db every few seconds is because you are caching something. Each user of my application can send a task (a request) for which the calculating time may vary from one up to several minutes. So it’s obvious that I’m forced to make him wait. But I don’t want to. I think that if I used a rails app to submit tasks and another app to give the response I would need a trick to notify a user that his task was calculated. That’s the reason I wanted to check the state of database to find out which tasks of which users are finished. Maybe should I use a queuing system or something like that? Performance is the issue. I will have about 2000 users, and wait for demands of about 100 users at once. Best regards, ---
**Author:** ![Jakub\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/3be4f8/32.png) [@Jakub\_N](https://www.ruby-forum.com/u/Jakub_N)\ **Post date:** [February 16, 2006, 9:22pm UTC](https://www.ruby-forum.com/t/action-when-database-changes/53811/6 "2006-02-16T21:22:03Z")
On 2/16/06, Jakub N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > calculated. That’s the reason I wanted to check the state of database > > > upon every request and recompute your values. Only in slow Java > > > > > > > > if there is a solution a bit more ‘elegant’: to trigger an action > > > > > > the proper time. The results goes to new row in another table which > > > > > > > > * * * > > > > > > E Factor Media // FN Interactive > > > Cheers! > > > [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails) > > > – > > > Kuba Nowak > > * * * > > Rails mailing list > removed\_email\_address@domain.invalid > [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails) Look at this article for an example of running a queue with RailsCron: [http://kylemaxwell.com/articles/2006/01/26/simple-emailqueue-for-rails](http://kylemaxwell.com/articles/2006/01/26/simple-emailqueue-for-rails) For something like this, I prefer to send the user an email informing him/her that the task is complete. O’Reilly Safari also sends emails in similar situations. – Kyle M. Chief Technologist E Factor Media // FN Interactive removed\_email\_address@domain.invalid 1-866-263-3261 ---
**Author:** ![Jakub\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/3be4f8/32.png) [@Jakub\_N](https://www.ruby-forum.com/u/Jakub_N)\ **Post date:** [February 15, 2006, 11:54pm UTC](https://www.ruby-forum.com/t/action-when-database-changes/53811/7 "2006-02-15T23:54:31Z")
Kyle beat me to the curl suggestion 🙂 However, after further thought, I’m wondering why you need all this complexity? The only reason I can see why you’d need to have the Rails app check the db every few seconds is because you are caching something. I would simply have the Rails app grab the data directly from the DB upon every request and recompute your values. Only in slow Java applications have I found caching very useful… On Wednesday, February 15, 2006, at 2:37 PM, Kyle M. wrote: > > > You could use the after\_save callback, along with the ruby http > > > I don’t know if this idea is correct, but I would like to know how to > > > [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails) > > * * * > > Rails mailing list > removed\_email\_address@domain.invalid > [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails) Cheers! –Dave T. [http://devlists.com](http://devlists.com) - Email list management [http://palmsphere.com](http://palmsphere.com) - Apps for your hand-held ---
**Author:** ![Jakub\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/3be4f8/32.png) [@Jakub\_N](https://www.ruby-forum.com/u/Jakub_N)\ **Post date:** [February 16, 2006, 9:50pm UTC](https://www.ruby-forum.com/t/action-when-database-changes/53811/8 "2006-02-16T21:50:07Z")
The approach I would take is to have the the task processor have a “completion” flag/timestamp in the database, and corresponding “has\_been\_read” flag/timestamp, or something along those lines. Any time the user requests a page in the app, check to see if there are any completed, unread notices and use the :flash to notify them somewhere in the layout. Think along the lines of a “New Mail” alert on a portal or webmail service. If you want something more proactively pushed out, maybe because the app window gets left open idle for long periods after task submission, maybe have a div in your layout reserved for that sort of notice and have a periodically\_call\_remote() check for newly completed jobs and put an elert in the div. Use it sparingly, though, to save the server from thousands of status checks a minute. Maybe only bring it into play in a view when the user has a pending submitted task. -sk Jakub N. wrote: > Dave T. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > However, after further thought, I’m wondering why you need all this > > complexity? The only reason I can see why you’d need to have the Rails > > app check the db every few seconds is because you are caching something. > > Each user of my application can send a task (a request) for which the > calculating time may vary from one up to several minutes. So it’s > obvious that I’m forced to make him wait. But I don’t want to. I think > that if I used a rails app to submit tasks and another app to give the > response I would need a trick to notify a user that his task was > calculated. That’s the reason I wanted to check the state of database > to find out which tasks of which users are finished. > > Maybe should I use a queuing system or something like that? > > Performance is the issue. I will have about 2000 users, and wait for > demands of about 100 users at once. > > Best regards,