belongs_to association without an extra table - ruby-on-rails

Question

I have a model Download, with a table downloads. downloads has a field called ip_address, which stores an ip address as an integer. I want to set up an IpAddress model, but without a ip_addresses table, so I can do stuff like
Download.find(1).ip_address.to_s # '127.0.0.1'
Download.find(1).ip_address.to_i # 2130706433
Download.find(1).ip_address.downloads # SELECT * FROM downloads WHERE ip_address='2130706433'
IpAddress.find(2130706433).downloads # SELECT * FROM downloads WHERE ip_address='2130706433'
I want it to behave like:
class Download < ActiveRecord::Base
belongs_to :ip_address, :foreign_key => :ip_address
end
class IpAddress < ActiveRecord::Base
set_primary_key :ip_address
has_many :downloads, :foreign_key => :ip_address
end
but without having a useless table of ip addresses.
Is this possible?
EDIT
I found that ruby already has a IPAddr class.
So I did this:
require 'ipaddr'
class Download < ActiveRecord::Base
attr_accessible :ip, ...
def ip
#ip ||= IPAddr.new(read_attribute(:ip), Socket::AF_INET)
end
def ip=(addr)
#ip = IPAddr.new(addr, Socket::AF_INET)
write_attribute(:ip, #ip.to_i)
end
def self.for_ip(addr)
where(:ip => IPAddr.new(addr, Socket::AF_INET).to_i)
end
end
Then I can do lots of cool stuff
Download.new(:ip => '127.0.0.1').save
Download.for_ip('127.0.0.1').first.ip.to_i # 2130706433

Answer 1

belongs_to is really meant to specify an association between objects in two tables. But you're right, unless you need to store other associated data, storing IP addresses in a table is fairly useless.
However, you can use scopes to accomplish what you will want. You could have something like this in your Download model:
class Download < ActiveRecord::Base
scope :for_ip, lambda { |x| where(:ip_address => x) }
end
Then you would call
Download.for_ip(2130706433)
To get a list of downloads for that IP.
You could also add a class method instead:
class Download < ActiveRecord::Base
def self.for_ip(x)
where(:ip_address => x)
end
end
That might be handy if you want to convert from string to numeric IP addresses.
And, if you want an IPAddress class, you can add a method like this:
class IPAddress
def initialize(ip)
#presumably do some stuff here
#ip = ip
end
def downloads
Download.for_ip(#ip)
end
end

Answer 2

IpAddress.find(2130706433).downloads # SELECT * FROM downloads WHERE ip_address='2130706433'
This is totally a semantics issue, but this should probably change if you have no IpAddress table (i.e. how can we find the IpAddress object 2130706433 in the database if there is no IpAddress table - unless you make IpAddress a container rather than a specific single ipaddress, otherwise do something like instantiate new ones with a constructer like IpAddress(2130706433).downloads).
Otherwise, though, I don't see any problems in not having the IpAddress table. Why do you need it to be belongs_to, rather than just another column?
You can keep the models/objects if you wish to access them in similar ways:
class Download < ActiveRecord::Base
##Whatever Download-model-specific code you have...
def ip_address
#If nil, initialize new object. Return object.
#ip_address ||= IpAddress(ip_address_val)
end
end
class IpAddress
def initialize(address)
#value = address
end
def downloads
Download.where(:ip_address_val => self.value)
end
end
EDIT:
You can override the accessor, like you're asking. You just have to be careful in your code to be particular about what you're asking for.
See this doc: http://ar.rubyonrails.org/classes/ActiveRecord/Base.html
Under section "Overwriting default accessors"
Basically, if you do override the value, and if you wish to access the DB value, you use read_attribute(attr_name), so the code might look like this:
class Download < ActiveRecord::Base
##Whatever Download-model-specific code you have...
def ip_address
#If nil, initialize new object. Return object.
#ip_address ||= IpAddress(read_attribute(:ip_address))
end
end
class IpAddress
def initialize(address)
#value = address
end
def downloads
Download.where(:ip_address => self.value)
end
end
Though things might get a little confusing in your code if you aren't careful.

Answer 3

Add set_table_name "downloads" to your IpAddress and remove the relationship between the 2 coz it already has the column name ip_address.
This will give you queries in following way
Download.find(1).ip_address.to_s # '127.0.0.1'
Download.find(1).ip_address.to_i # 2130706433
IpAddress.find(Download.find(1).ip_address) # SELECT * FROM downloads WHERE ip_address='2130706433'
IpAddress.find(2130706433) # SELECT * FROM downloads WHERE ip_address='2130706433'