using same validation-set in more than one class

rubyonrails-talk
1

hello, lets describe my situation: i have two classes which have a lot same validations defined ... to stay DRY i want to put them in one place and use it within both ActiveRecord classes.

- i think subclassing is not possible because both classes are AR of different tables

- tried to include a module but this didnt work either:

module CustomExtensions validates_length_of :a, :in => 1..10 validates_length_of :b, :in => 1..20 end

class A < AR::Base   include CustomExtensions end

thx for help!

2

hello, lets describe my situation: i have two classes which have a lot same validations defined ... to stay DRY i want to put them in one place
and use it within both ActiveRecord classes.

- i think subclassing is not possible because both classes are AR of different tables

- tried to include a module but this didnt work either:

module CustomExtensions validates_length_of :a, :in => 1..10 validates_length_of :b, :in => 1..20 end

class A < AR::Base include CustomExtensions end

nearly there!

module CommonStuff    def self.included(base)      base.instance_eval do        validates_length_of :a, :in => 1..10        validates_length_of :b, :in => 1..20      end    end    ... end

class A < AR::Base    include CommonStuff end

3

hey thx for the quick reply .. it worked! i am just wondering why its "instance_eval" and not "class_eval"... should the validations not be applied to the whole class?

4

hey thx for the quick reply .. it worked! i am just wondering why its "instance_eval" and not "class_eval"... should the validations not be applied to the whole class?

In this particular case it doesn't make any difference. instance_eval
means that self will be the base class (ie A) when the validates_*
calls are made. module_eval (which is the same as class eval) would do
the same thing (it would be different if we were defining methods
inside the eval block, but we're not)

Fred

5

Frederick Cheung wrote:

In this particular case it doesn't make any difference. instance_eval means that self will be the base class (ie A) when the validates_* calls are made. module_eval (which is the same as class eval) would do the same thing (it would be different if we were defining methods inside the eval block, but we're not)

i see.. you mean if we would do this??

def self.included(base)   class_eval do     ...   end end

6

Frederick Cheung wrote:

In this particular case it doesn't make any difference. instance_eval means that self will be the base class (ie A) when the validates_* calls are made. module_eval (which is the same as class eval) would
do the same thing (it would be different if we were defining methods inside the eval block, but we're not)

i see.. you mean if we would do this??

I mean module CommonStuff   def self.included(base)     base.instance_eval do       validates_length_of :a, :in => 1..10       validates_length_of :b, :in => 1..20     end   end

has the same effect as

module CommonStuff   def self.included(base)     base.class_eval do       validates_length_of :a, :in => 1..10       validates_length_of :b, :in => 1..20     end   end

but if your eval block had

def foo end then the method would be added in different places (A.foo instead of
A.new.foo)

Fred

7

Frederick Cheung wrote:

oh i see now... thanks for your time! learned something again