Rails 2.3 - implement dynamic named_scope using mixin
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29-04-2021 - |
Pergunta
I use the following method_missing implementation to give a certain model an adaptable named_scope filtering:
class Product < ActiveRecord::Base
def self.method_missing(method_id, *args)
# only respond to methods that begin with 'by_'
if method_id.to_s =~ /^(by\_){1}\w*/i
# extract column name from called method
column = method_id.to_s.split('by_').last
# if a valid column, create a dynamic named_scope
# for it. So basically, I can now run
# >>> Product.by_name('jellybeans')
# >>> Product.by_vendor('Cyberdine')
if self.respond_to?( column.to_sym )
self.send(:named_scope, method_id, lambda {|val|
if val.present?
# (this is simplified, I know about ActiveRecord::Base#find_by_..)
{ :conditions => ["#{base.table_name}.#{column} = ?", val]}
else
{}
end
})
else
super(method_id, args)
end
end
end
end
I know this is already provided by ActiveRecord::Base using find_by_<X>
, but I'm trying to go a little bit beyond the example I've given and provide some custom filtering taylored to my application. I'd like to make it available to selected models w/o having to paste this snippet in every model class. I thought of using a module and then mixing it in the models of choice - I'm just a bit vague on the syntax.
I've gotten as far as this when the errors started piling up (am I doing this right?):
module GenericFilter
def self.extended(base)
base.send(:method_missing, method_id, *args, lambda { |method_id, args|
# ?..
})
end
end
Then I hope to be able to use it like so:
def Product < ActiveRecord::Base
include GenericFilter
end
def Vendor < ActiveRecord::Base
include GenericFilter
end
# etc..
Any help will be great - thanks.
Solução
Two ways of achieving this
module GenericModule def self.included(base) base.extend ClassMethods end module ClassMethods def methods_missing #.... end end end class YourModel include GenericModule .. end
or
module GenericModule def method_missing #... end end class MyModel extend GenericModule end
I would suggest using the first one, its seems cleaner to me. And as general advise, I'd avoid overriding method_missing :).
Hope this helps.
Outras dicas
You need to define the scope within the context of the class that is including your mixin. Wrap your scopes in including_class.class_eval and self will be correctly set to the including_class.
module Mixin
def self.included(klass)
klass.class_eval do
scope :scope_name, lambda {|*args| ... }
end
end
end
class MyModel
include Mixin
end