Example of how to DRY up complex Grails validation logic and share it across different domain objects.

MyDomain.groovy

class MyDomain {
        ...
        static constraints = {
              items(validator: requiresAtleastOne)
        }
}

Validators.groovy

class Validators {
    
    static final confirmPasswordValidator = { value, command ->
        if (command.password != command.confirmPassword) {
            return 'command.confirmPassword.error.mismatch'
        }
    }
 
    
    static def requiresAtleastOne =  {val, obj->
        if(!val?.size()){
            return "default.requires.atleast.one"
        }
    }
}