In the Rails world, your class names tend to be CamelCased. Instances of that class can be assigned toVariables of_any_look. Standard Ruby convention is to keep capital letters out of variables, except for Constants, which are always capitalized.
In RoR, when you're doing a datamigration, the data_migrations table will always link to your DataMigration model. :symbols are something else entirely - they're an object with a name. You can think of them as something like the interpreted language's answer to the enumerated integer - they're objects with O(1) comparison, constant size, and once you declare them and pay for the memory leak of creating them you never have to re-allocate memory for them, like you would for strings. However, they're not strings! If you care about the content of the symbol, don't use a symbol. If you just care about the symbol being a reference for something, it's a great choice - which is why you see them all over the place in the RoR world for option hashes: We don't care that :if means 'if' which is a conditional in the English language, we just need a constant, agreed-upon, and memorable way to refer to something passed to the method. Symbols are also closely tied to the way that methods are declared, which is why you see things like: before_filter :do_this. ... because it's much faster to send :do_this to the controller for evaluation than it is to eval 'do_this' and get the parser involved. On Sep 22, 4:33 pm, dschruth <[EMAIL PROTECTED]> wrote: > Thanks Dan that worked! > > I suppose at some point here I should learn ruby. :) The language > (and rails platform) give you so much for free and the syntax is so > intuitive that Its easy to get way in over your head fast when the > subtle but inevitable complexities start to counteract the initial > advantages! (perhaps) > > At the very least I should figure out the difference between these > three object naming conventions > > Subscriber # CamelNotation (the class?) > subscriber # lowercase_underscore (an instantiation of the class? > ie an object?) > :subscriber # :colon_lowercase_underscore (an accessor? what ever > that is.) > > (not to mention the plural vs singular conventions) > > Its very confusing for newbies > > Thanks though, this one trick should keep me from stumbling over my > own ignorance for a while. > > Dave > > On Sep 22, 1:12 pm, Dan Manges <[EMAIL PROTECTED]> wrote: > > > I think I understand what you're trying to do - you don't need to do a > > find. Implement the method like I suggested. > > > has_many :subscribers, :through => :subscriptions > > > def some_method > > subscribers.calculate(:max, :date_of_birth) > > end > > > "subscribers" references the has_many :through association proxy. It > > will take care of setting the proper joins and conditions to run the > > calculation only for the associated records. In my example with > > calculate(:max, :date_of_birth), the method would find the date of > > birth for the youngest person subscribed to that magazine. Make sure > > you're using lowercase "subscribers", not capitalized "Subscriber" > > > -Dan Mangeshttp://www.dcmanges.com/blog > > > On Sep 22, 1:41 pm, dschruth <[EMAIL PROTECTED]> wrote: > > > > Lets just use yourMagazine/Subscriberexample for now. > > > > I want to do something like this: > > > -------------------------------------------------------- > > > classMagazine > > > def subscriber_salaries > > > Subscriber.calculate(:sum, :salary, :conditions => "magazine_id = > > > " + id.to_s) # PGError: ERROR: column "magazine_id" does not > > > exist > > > end > > > end > > > -------------------------------------------------------- > > > But of course there is no "magazine_id" in the subscribers table > > > anymore because we've switched away from "subscriberhas many > > > subscriptions". > > > > Like you said, I'm guessing I should probably use a "find" like so: > > > > some_model =Subscriber.find( ??? ) > > > some_model.Subscriber.calculate(:sum, :salary) > > > > But i don't know how to do that quite yet. (what goes in the ???) > > > > Ideas? > > > > On Sep 21, 12:40 pm, DanManges<[EMAIL PROTECTED]> wrote: > > > > > Hi Dave, > > > > > Can you post more of your code? If you're going through the > > > > association proxies, the calculation should work. Is 'table1' in your > > > > example a target of a has_many :through association? So do you have it > > > > set up something like this? > > > > > class SomeModel < ActiveRecord::Base > > > > has_many :table1, :through => :something > > > > end > > > > > some_model = SomeModel.find(:first) > > > > some_model.table1.sum(:enrich_bead_count_hemo) > > > > > If you're just doing Table1.sum(:enrich_bead_count_hemo), (note the > > > > capitalized Table1), then it would be for all the rows, not just the > > > > associated ones. > > > > > -DanMangeshttp://www.dcmanges.com/blog > > > > > On Sep 21, 2:05 pm, dschruth <[EMAIL PROTECTED]> wrote: > > > > > > Thanks for the response, > > > > > > However, I tired what you suggested but only got to the same point as > > > > > before. > > > > > > Both of these ways: > > > > > > table1.calculate(:sum, :enrich_bead_count_hemo, > > > > > OR > > > > > table1.sum(:enrich_bead_count_hemo > > > > > > give me the same answer: at total of *all* the rows in the other > > > > > table. But I want a sum of *just* the *associated* rows. > > > > > > I was able to do this when the tables where directly related (with > > > > > a :condition statement). But I don't quite know how to do that yet > > > > > for HABTM or "has many :foo => :through" > > > > > > Dave > > > > > > On Sep 20, 9:53 pm, DanManges<[EMAIL PROTECTED]> wrote: > > > > > > > You should take advantage of the association proxies. Something like > > > > > > this should work. > > > > > > > classMagazine > > > > > > has_many :subscriptions > > > > > > has_many :subscribers, :through => :subscriptions > > > > > > end > > > > > > > class Subscription > > > > > > belongs_to :magazine > > > > > > belongs_to :subscriber > > > > > > end > > > > > > > classSubscriber > > > > > > has_many :subscriptions > > > > > > end > > > > > > > Now you can do calculations like this: > > > > > > > classMagazine > > > > > > def youngest_subscriber_birthday > > > > > > subscribers.calculate(:max, :date_of_birth) > > > > > > end > > > > > > end > > > > > > > You should be able to do the calculation the same way for your > > > > > > 'enrich_bead_count_hemo'. > > > > > > > -DanMangeshttp://www.dcmanges.com/blog > > > > > > > On Sep 20, 10:06 pm, dschruth <[EMAIL PROTECTED]> wrote: > > > > > > > > Hi, > > > > > > > > I'm trying to sum up the records in a related table that used to > > > > > > > just > > > > > > > be a child table. This line used to work: > > > > > > > > table1.sum(:enrich_bead_count_hemo, :conditions => "table2_id = " > > > > > > > + > > > > > > > id.to_s) > > > > > > > > now I've got an intermediate "has and belongs to many" = HABTM > > > > > > > table > > > > > > > inbetween them. Could somebody help me figure out how to sum > > > > > > > across > > > > > > > two tables? I'm thinking i might have to use the custom SQL > > > > > > > "join" > > > > > > > attribute of the sum method. > > > > > > > > Thanks, > > > > > > > > Dave > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
