If you are using Rails and you find yourself fighting validations more often than you would like to, then you should consider watching my talk I gave at the London Ruby User Group this February about on dry-validation.
I will present the API surface which uses a schema based declarative approach and I will compare it with the classic ActiveModel:
You can find the talk here
Code examples are here
If you have any question, feel free to reach me out in the comments or on Twitter at https://twitter.com/mottalrd