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I have one concern and two classes which include it. In the concern, I defined one variable. Here is the concern and the two models:
module UserInstance extend ActiveSupport::Concern included do ACTIVE = 'active' end end class Guardian < ActiveRecord::Base include UserInstance end class Student < ActiveRecord::Base include UserInstance end I'm getting this warnings:
/app/app/models/concerns/user_instance.rb:12: warning: already initialized constant UserInstance::ACTIVE /app/app/models/concerns/user_instance.rb:12: warning: previous definition of ACTIVE was here I guess that once it loads one class (like Guardian), it also loads the constant, and loading the other class tries to load the constant again, and then the warning is given. How can I avoid this without having to put the constants in the two models? Thanks
685
No need to require ActiveSupport. Usage example: class User; def self. lookup; const_get('SomeClassName);end; end User. lookup will return class itself.
Overview. Do not define constants within a block, since the block's scope does not isolate or namespace the constant in any way. If you are trying to define that constant once, define it outside of the block instead, or use a variable or method if defining the constant in the outer scope would be problematic.
The method definitions look similar, too: Module methods are defined just like class methods. As with class methods, you call a module method by preceding its name with the module's name and a period, and you reference a constant using the module name and two colons.
I just came across the same bug, when trying to implement concerns.
The guide I was following also but the Constant in the included block and seemed to have no error. But my log threw me exactly the same error you have.
After some trial and error, I just removed the Constant from the block and put it outside, like:
module UserInstance extend ActiveSupport::Concern included do end ACTIVE = 'active' end This way I could still access the Constant, but didn't get anymore errors. I'm not 100% sure that this is the right way, but it worked and I couldn't find any errors, so I will go with it.
I would like to now if this works for you too!
191
Using base solved the problem for me.
module UserInstance extend ActiveSupport::Concern # https://api.rubyonrails.org/v6.0.0/classes/ActiveSupport/Concern.html#method-i-included included do |base| base.const_set :ACTIVE, "active" # direct const creation in this included block will attach the const to the concern module, not the including class # so if you have multiple classes including the same concern, it will try to difine the same const to the same module # ACTIVE = "active" end end If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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