I posted a previous message about overriding initialize... because I was having issues setting some of the parameters. I have a Page model that has: attr_accessible :url, :title, :doc, :domain and it's called via: Page.new(:url => 'http://www.yahoo.com') Since I'm only passing in the url to new, I needed to set the other parameters. I was trying to do this via an after_initialize callback which wasn't working so tried overriding initialize... still not working. What I found out was that in my after_initialize, I was referring to title as @title which is why it was not working. I switched it to self.title and it works fine. My question is - why?
on 2012-12-21 18:38
on 2012-12-21 18:44
On Dec 21, 2012, at 12:37 PM, Dan Brooking wrote: > What I found out was that in my after_initialize, I was referring to title as @title which is why it was not working. I switched it to self.title and it works fine. > > My question is - why? @title is an instance variable. Until you set it, it doesn't exist. Having a method on the model called title (or an accessor, or some other Rails magick) does not instantiate that method's return until and unless you ask for it by calling the method. Calling self.method_name just makes it clear which same-named method you really mean. Self is implied much of the time, but when you have all the many method_missing options available, it might not be the first one such that gets called. Walter
on 2012-12-21 19:14
So is the way I'm doing it right? Or just a way I happened to hack it to work? The way my code was looking was basically: Page.new(:url => 'http://www.yahoo.com') class Page < ActiveRecord::Base attr_accessible :url, :title after_initialize :parse_page_params def parse_page_params @title = "test" end and this wasn't working... I understand what you said above about the instance variables, methods, initializing, etc.. but still a little unclear about why that code doesn't work as I'm setting it. Is it because Rails uses the method name of title which hasn't been initailized in my assignment above?
on 2012-12-21 19:41
On Dec 21, 2012, at 1:12 PM, Dan Brooking wrote: > > def parse_page_params > @title = "test" > end > Have a look at the documentation for after_initialize -- it runs once, after Rails itself is fully initialized. Is that the point at which you mean to instantiate the instance variable @title? Which instance of its class would it attach to? Can you please describe what you intend to do with @title -- where it's going to be used? Walter
on 2012-12-21 22:37
I would use a before_save or what it is called if I were you. Am 21.12.2012 19:40 schrieb "Walter Lee Davis" <email@example.com>:
on 2012-12-21 22:40
What I'm trying to do is parse out the title and then save it to the DB for quick display on the webpage. I could do a before_save, hadn't thought of that, but would I have the same issues? I'm basically doing a Page.new(...), a few lines of validation, and then Page.save() so before_save would be ok I guess. Is there typically a standard way of doing things?
on 2012-12-21 23:18
On Dec 21, 6:12pm, Dan Brooking <dmbrook...@gmail.com> wrote: > instance variables, methods, initializing, etc.. but still a little unclear > about why that code doesn't work as I'm setting it. Is it because Rails > uses the method name of title which hasn't been initailized in my > assignment above? > Because rails doesn't use individual instance variables to store your attributes (whether they've been marked as attr_accessible makes no difference) title = "foo" Doesn't work because ruby assumes that you want to assign to the local variable called title. Doing self.title = makes it clear that you want to call the title= accessor Fred
on 2012-12-22 13:21
I do something similar in a project of mine. I have an API key and retrieve user information after he logs in. This works very fine in an after-find, why should that not work in a before_save? Can't provide the source right now. I have no access until Jan 8th. Am 21.12.2012 22:39 schrieb "Dan Brooking" <firstname.lastname@example.org>:
on 2012-12-22 21:06
On Friday, 21 December 2012 13:12:35 UTC-5, Dan Brooking wrote: > > assignment above? > > It sounds like you've got attr_accessible and attr_accessor somewhat entangled in your mental model. They aren't really the same thing at all: - attr_accessible: specifies which attributes are mass-assignable (through things like Page.new(:some_attribute => 'foo')) and which have to be assigned individually. - attr_accessor: creates two accessor methods that wrap an instance variable. So this: attr_accessor :something is shorthand for this: def something @something end def something=(v) @something = v end Occasionally you'll even see both used for a particular name, as the developer wants to create an attribute that isn't persisted to the database but can be mass-assigned (from a form submission, for instance). --Matt Jones
on 2012-12-23 08:29
Frederick Cheung wrote in post #1089897: > > Because rails doesn't use individual instance variables to store your > attributes (whether they've been marked as attr_accessible makes no > difference) > > title = "foo" > > Doesn't work because ruby assumes that you want to assign to the local > variable called title. Doing self.title = makes it clear that you want > to call the title= accessor > While true, that has nothing to do with the op's problem--the op is assigning to an @ variable, and an @ variable, like @title, can never be a local variable. There is only one way for ruby to interpret an assignment like: @title = some_value >Is there typically a standard way of doing things? Yes. Always use the accessor method to set or get the value of an instance variable. Here is an example of how things can go wrong: class Dog def title=(val) @title = val.capitalize end def title @title end def do_stuff @title = "mr." @title + " Dog" end end puts Dog.new.do_stuff --output:-- mr. Dog And here is how to correct the problem: class Dog def title=(val) @title = val.capitalize end def do_stuff self.title = "mr." title + " Dog" end end puts Dog.new.do_stuff What you did is bypass an accessor method, which you did not define and therefore are blissfully unaware of what it does, and your results showed that the accessor method did something critical. The solution is similar to why you should call super inside your class's initialize() method when you inherit from a complicated class hierarchy: you need to let classes higher up in the chain proceed with the machinations they require to set up everything correctly.
on 2012-12-23 08:49
7stud -- wrote in post #1089991: > > And here is how to correct the problem: > > class Dog > def title=(val) > @title = val.capitalize > end > > def do_stuff > self.title = "mr." > title + " Dog" > end > end > > puts Dog.new.do_stuff > > I left out the getter: class Dog def title=(val) @title = val.capitalize end #MISSING getter ********** def title @title end def do_stuff self.title = "mr." title + " Dog" end end puts Dog.new.do_stuff --output:-- Mr. Dog