I have a non-database-backed class in Ruby:
class User
attr_accessor :countries
end
I want countries to simply be an array of ISO country codes (US, GB, CA, AU, etc) and I don't want to build a separate model to hold each. Is there a magic way to make Ruby understand that :countries is an array and treat it accordingly, or do I need to write the countries and countries= methods?
I tried just setting the countries array with user.countries = ['US'], and I'm getting a NoMethodError.
The type of a variable doesn't matter in Ruby.
attr_accessor just creates getter and setter methods that set and return instance variables; @countries in this case. You can set the instance variable to your array, or use the setter:
class User
attr_accessor :countries
def initialize
@countries = %w[Foo Bar Baz]
# Or...
self.countries = %w[Foo Bar Baz]
end
end
> puts User.new.countries
=> ["Foo", "Bar", "Baz"]
Personally I prefer using the instance variable instead of self.xxx; it's too easy to forget the self. bit and you end up setting a local variable, leaving the instance variable nil. I also think it's ugly.
If the countries won't be changing between instances, why not a constant?
Edit/Clarification
Tadman's point is well-taken, e.g., this diatribe on state. The circumtances under which I don't care about that are limited to small, self-controlled, stand-alone classes. There are inherent risks in making those assumptions, the level of those risks is project-dependent.
attr_accessor can lead to some slip-ups if you've overridden either of the getter or setter methods. If you do a lot of JavaScript where this is absolutely required, being disciplined about adding self isn't a big deal.
attr_accessor and overriding one or the other, I'd say you're doing it wrong. IMO attr_accessor communicates that it's an accessor, not a method that performs other logic.
self.countries.push("bla") won't workLooks like countries should be a constant:
class User
COUNTRIES = %w(
AF AX AL DZ AS AD AO AI AQ AG AR AM AW AU AT AZ BS BH BD BB BY BE BZ BJ BM
BT BO BQ BA BW BV BR IO BN BG BF BI KH CM CA CV KY CF TD CL CN CX CC CO KM
CG CD CK CR CI HR CU CW CY CZ DK DJ DM DO EC EG SV GQ ER EE ET FK FO FJ FI
FR GF PF TF GA GM GE DE GH GI GR GL GD GP GU GT GG GN GW GY HT HM VA HN HK
HU IS IN ID IR IQ IE IM IL IT JM JP JE JO KZ KE KI KP KR KW KG LA LV LB LS
LR LY LI LT LU MO MK MG MW MY MV ML MT MH MQ MR MU YT MX FM MD MC MN ME MS
MA MZ MM NA NR NP NL NC NZ NI NE NG NU NF MP NO OM PK PW PS PA PG PY PE PH
PN PL PT PR QA RE RO RU RW BL SH KN LC MF PM VC WS SM ST SA SN RS SC SL SG
SX SK SI SB SO ZA GS SS ES LK SD SR SJ SZ SE CH SY TW TJ TZ TH TL TG TK TO
TT TN TR TM TC TV UG UA AE GB US UM UY UZ VU VE VN VG VI WF EH YE ZM ZW
).freeze
end
User::COUNTRIES.include? "US" #=> true
freeze prevents modifications:
User::COUNTRIES.delete "US" #=> RuntimeError: can't modify frozen Array
Update
The problem here is that your countries array has to be persisted somehow. You are mentioning has_many so Rails seems to be involved. You can use ActiveRecord's serialize method:
class User < ActiveRecord::Base
serialize :countries
end
This will save the countries attribute to the database as an object and retrieve it as such:
u = User.new
u.countries = ["US", "CA"]
u.save
u = User.last
u.countries
#=> ["US", "CA"]
It's converted to and from YAML internally, so the users table looks like:
mysql> SELECT * FROM users;
+----+-------------------+---------------------+---------------------+
| id | countries | created_at | updated_at |
+----+-------------------+---------------------+---------------------+
| 1 | ---\n- US\n- CA\n | 2013-09-24 18:24:03 | 2013-09-24 18:24:03 |
+----+-------------------+---------------------+---------------------+
1 row in set (0,00 sec)
def self.countries; COUNTRIES; end. This might seem pointless, but it allows subclasses to override that method if required and avoids exposing the structure of this constant to other parts of your code that need access to an array.
attr_accessorthis, you will get freecountriesandcountries=:) :)user.countries = [:gb, :au]?attr_accessorprovides thecountriesandcountries=methods, but there is nothing to stop you setting@countriesto something other than an array. If you want to do array things, like<<andlengthto it then you need to write your own methods.