Custom type-casting with ActiveRecord, Virtus and dry-types

In Drop this before validation and just use a setter method I showed you how to avoid a common pattern of using before_validation to fix the data. Instead I proposed you just overwrite the setter, call your custom logic there and use super . I also showed you what you can do if you can’t easily call super .

But sometimes to properly transform the incoming data or attributes you just need to improve the type-casting logic. And that’s it. So let’s see how you can add your custom typecasting rules to a project.

And let’s continue with the simple example of stripped string.

Active Record 4.2+

class StrippedString < ActiveRecord :: Type :: String def cast_value ( value ) value . to_s . strip end end

class Post < ActiveRecord :: Base attribute :title , StrippedString . new end

p = Post . new ( title: " Use Rails " ) p . title # => "Use Rails"

Virtus

class StrippedString < Virtus :: Attribute def coerce ( value ) value . to_s . strip end end

class Address include Virtus . model include ActiveModel :: Validations attribute :country_code , String attribute :street , StrippedString attribute :zip_code , StrippedString attribute :city , StrippedString attribute :full_name , StrippedString validates :country_code , :street , :zip_code , :city , :full_name , presence: true end

a = Address . new ( city: " Wrocław " ) a . city # => "Wrocław"

dry-types 0.6

module Types include Dry :: Types . module StrippedString = String . constructor ( -> ( val ){ String ( val ). strip }) end

class Post < Dry :: Types :: Struct attribute :title , Types :: StrippedString end

p = Post . new ( title: " Use dry " ) p . title # => "Use dry"

Conclusion

If you want to improve type casting for you Active Record class or if you need it for a different layer (e.g. a Form Object or Command Object) in both cases you are covered.

Historically, we have been using Virtus for that non-persistable layers. But with the recent release of dry-types (part of dry-rb) we started also investigating this angle as it looks very promising. I am very happy with the improvements added between 0.5 and 0.6 release. Definitelly a step in a right direction.

Summary

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