# Statistics table via a trigger **URL:** \ **Category:** Rails\ **Created:** [October 1, 2008, 6:13am UTC](https://www.ruby-forum.com/t/statistics-table-via-a-trigger/149916 "2008-10-01T06:13:57Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![chovy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ecd19e/32.png) [@chovy](https://www.ruby-forum.com/u/chovy)\ **Post date:** [October 1, 2008, 6:13am UTC](https://www.ruby-forum.com/t/statistics-table-via-a-trigger/149916/1 "2008-10-01T06:13:57Z")
I’m trying to implement something similar to a historical price chart, where I save the prices when they change to a “stats” table. I’d like to take the current value and save it to a statistics model before it gets updated with the new value. Is there a way to do it with a trigger or should I just save the value in two different models? Something like this: @book = Book.find(params[:id]) @stats = Stat.new() puts @book.price #=\> $10.00 @stats.book\_id = @book.id @stats.price = @book.price @book.price = $20.00 @book.save() @stats.save() ---
**Author:** ![chovy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ecd19e/32.png) [@chovy](https://www.ruby-forum.com/u/chovy)\ **Post date:** [October 1, 2008, 4:06pm UTC](https://www.ruby-forum.com/t/statistics-table-via-a-trigger/149916/2 "2008-10-01T16:06:26Z")
On Tue, Sep 30, 2008 at 9:13 PM, Anthony E. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Something like this: > @book.price = $20.00 > > @book.save() > @stats.save() Anthony, Is Book the only model that you’ll be doing this for? …or are there other models that will use this historical log of prices? There’s a few options here. One, you could add method to be called by after\_save to check the price previously stored with the new one… if they are different… add a new entry to the historical log. Another option is to not store prices in the Book model and only in another table called something like BookPrice. book has\_many book\_prices Then you can scope book\_prices for current to do something like: book.book\_prices.current.price # =\> get the current price book.book\_prices.each { |book\_price| … } # =\> iterate through all book prices Anyhow, there’s a few options to throw your way. Good luck! Cheers, Robby – Robby R. Chief Evangelist, Partner PLANET ARGON, LLC design // development // hosting > **[Planet Argon](https://www.planetargon.com/)** > > Planet Argon is a Ruby on Rails development agency specializing in maintenance and support for existing Rails apps. Based in Portland, OR, Planet Argon has been a member of the Rails community since 2004. [http://www.robbyonrails.com/](http://www.robbyonrails.com/) aim: planetargon +1 503 445 2457 +1 877 55 ARGON [toll free] +1 815 642 4068 [fax] ---
**Author:** ![chovy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ecd19e/32.png) [@chovy](https://www.ruby-forum.com/u/chovy)\ **Post date:** [October 2, 2008, 12:30am UTC](https://www.ruby-forum.com/t/statistics-table-via-a-trigger/149916/3 "2008-10-02T00:30:32Z")
Book having many :prices does make sense. That way you get to keep the history of the price of the book. Of course, the latest price in the association is the current price. Ramon T. On Thu, Oct 2, 2008 at 2:05 AM, Anthony E. ---
**Author:** ![chovy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ecd19e/32.png) [@chovy](https://www.ruby-forum.com/u/chovy)\ **Post date:** [October 2, 2008, 1:01am UTC](https://www.ruby-forum.com/t/statistics-table-via-a-trigger/149916/4 "2008-10-02T01:01:28Z")
Ramon T. wrote: > Book having many :prices does make sense. That way you get to keep > the history of the price of the book. Of course, the latest price in > the association is the current price. > > Ramon T. The problem with that is to get the current price (most uses cases) I have to scan the entire ‘prices’ table. I’d rather do it in such a way that it only saves the current price, year, edition, etc. to a “stats” whenever the book is updated (without any explicit association). ---
**Author:** ![chovy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ecd19e/32.png) [@chovy](https://www.ruby-forum.com/u/chovy)\ **Post date:** [October 1, 2008, 8:05pm UTC](https://www.ruby-forum.com/t/statistics-table-via-a-trigger/149916/5 "2008-10-01T20:05:44Z")
Robby R. wrote: > On Tue, Sep 30, 2008 at 9:13 PM, Anthony E. > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > Something like this: > > @book.price = $20.00 > > > > @book.save() > > @stats.save() > > Anthony, > > Is Book the only model that you’ll be doing this for? …or are there > other models that will use this historical log of prices? > > There’s a few options here. One, you could add method to be called by > after\_save to check the price previously stored with the new one… if > they are different… add a new entry to the historical log. > > Another option is to not store prices in the Book model and only in > another table called something like BookPrice. > > book has\_many book\_prices > > Then you can scope book\_prices for current to do something like: > > book.book\_prices.current.price # =\> get the current price > > book.book\_prices.each { |book\_price| … } # =\> iterate through all > book prices > > Anyhow, there’s a few options to throw your way. Good luck! > > Cheers, > Robby Thanks Robby. I will be doing this for one model for now, perhaps others down the road. The “Book” model has numeric attributes that I want to save into a “statistics” table so I can draw a line-graph over time from it. Other attributes would be archived as well. Its sounds to be a before\_update would give me access to the current price. And I don’t want to keep the current price in a stats table because that table will eventually grow and slow down the regular query. ## book id title price edition year ## stats id book\_id price edition year created\_at updated\_at Ideally sans-rails the stats table would be populated with a trigger when the book table is updated. There book will definitely “has\_many :stats” but I don’t really want that association to be queried every time I get a regular book object, only when I build the stats page. ---
**Author:** ![chovy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ecd19e/32.png) [@chovy](https://www.ruby-forum.com/u/chovy)\ **Post date:** [October 2, 2008, 1:20am UTC](https://www.ruby-forum.com/t/statistics-table-via-a-trigger/149916/6 "2008-10-02T01:20:16Z")
On Wed, Oct 1, 2008 at 4:01 PM, Anthony E. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > have to scan the entire ‘prices’ table. _sniff_ I smell premature optimization. 😉 Seriously, with database indexes… this is doubtful to be an issue. If it’s ever an issue you can cache the current price in the book model, but really… I wouldn’t be concerned about that for a while. > I’d rather do it in such a way that it only saves the current price, > year, edition, etc. to a “stats” whenever the book is updated (without > any explicit association). This is the case either way. Just not convinced you need to cache this in the Book model from the get-go, which is what you’re leaning toward. Cheers, Robby – Robby R. Chief Evangelist, Partner PLANET ARGON, LLC design // development // hosting > **[Planet Argon](https://www.planetargon.com/)** > > Planet Argon is a Ruby on Rails development agency specializing in maintenance and support for existing Rails apps. Based in Portland, OR, Planet Argon has been a member of the Rails community since 2004. [http://www.robbyonrails.com/](http://www.robbyonrails.com/) aim: planetargon +1 503 445 2457 +1 877 55 ARGON [toll free] +1 815 642 4068 [fax] ---
**Author:** ![chovy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ecd19e/32.png) [@chovy](https://www.ruby-forum.com/u/chovy)\ **Post date:** [October 3, 2008, 11:28am UTC](https://www.ruby-forum.com/t/statistics-table-via-a-trigger/149916/7 "2008-10-03T11:28:00Z")
Anthony E. wrote: > Robby R. wrote: > > > On Wed, Oct 1, 2008 at 4:01 PM, Anthony E. > > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > > have to scan the entire ‘prices’ table. > > > > _sniff_ I smell premature optimization. 😉 > > > > Seriously, with database indexes… this is doubtful to be an issue. > > If it’s ever an issue you can cache the current price in the book > > model, but really… I wouldn’t be concerned about that for a while. > > > > > I’d rather do it in such a way that it only saves the current price, > > > year, edition, etc. to a “stats” whenever the book is updated (without > > > any explicit association). > > > > This is the case either way. Just not convinced you need to cache this > > in the Book model from the get-go, which is what you’re leaning > > toward. > > Thanks Robby, you may indeed be correct. > > Is it safe to say your recommendation is to create a model for each > statistical attribute I want to archive? > > ie: > Price > Year > Edition > > …and associate them to the Book via: has\_many and then use the most > recent as the current price? I can’t get the save to work across the association. The price is coming from a backend system un-related to rails so I have got the data itself no problem with “get\_price” and saving it to self.price is fine…but I can’t refactor this into saving to another model (ie: prices) Book \< ActiveRecord::Base has\_many :prices before\_save :get\_price after\_save :set\_price def get\_price price = Legacy::Data.new().price end At this point my understanding breaks down…how do I save that “get\_price” value to the “Prices” model? #brokenzy def set\_price @price = self.prices.new @price.price = self.price end ---
**Author:** ![chovy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/ecd19e/32.png) [@chovy](https://www.ruby-forum.com/u/chovy)\ **Post date:** [October 2, 2008, 2:45am UTC](https://www.ruby-forum.com/t/statistics-table-via-a-trigger/149916/8 "2008-10-02T02:45:39Z")
Robby R. wrote: > On Wed, Oct 1, 2008 at 4:01 PM, Anthony E. > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > have to scan the entire ‘prices’ table. > > _sniff_ I smell premature optimization. 😉 > > Seriously, with database indexes… this is doubtful to be an issue. > If it’s ever an issue you can cache the current price in the book > model, but really… I wouldn’t be concerned about that for a while. > > > I’d rather do it in such a way that it only saves the current price, > > year, edition, etc. to a “stats” whenever the book is updated (without > > any explicit association). > > This is the case either way. Just not convinced you need to cache this > in the Book model from the get-go, which is what you’re leaning > toward. Thanks Robby, you may indeed be correct. Is it safe to say your recommendation is to create a model for each statistical attribute I want to archive? ie: Price Year Edition …and associate them to the Book via: has\_many and then use the most recent as the current price?