# How to perform checks based on the result of the previous check
**URL:** https://discourse.dry-rb.org/t/how-to-perform-checks-based-on-the-result-of-the-previous-check/340
**Category:** dry-validation
**Created:** [September 13, 2017, 1:19am UTC](https://discourse.dry-rb.org/t/how-to-perform-checks-based-on-the-result-of-the-previous-check/340 "2017-09-13T01:19:04Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@bethesque](https://discourse.dry-rb.org/u/bethesque)
#### Post date: [September 13, 2017, 1:19am UTC](https://discourse.dry-rb.org/t/how-to-perform-checks-based-on-the-result-of-the-previous-check/340/1 "2017-09-13T01:19:04Z")
I would like to assert that a value is a string is not blank (eg. " "). If I submit a number, I want only the message “must be a string” to appear, however, the “cannot be blank” message also appears. I have tried to debug this, and it seem that the `not_blank?` rule is failed automatically if the `str?` rule fails, as my debugger did not break when put in the `not_blank?` method. Is there a way to short circuit the checking, so that `not_blank?` is only checked if `str?` is true? I’m sure this has been answered before, however, I’ve had a bit of a search and cannot find an answer, and I’m not sure of the terms to search on. Thanks in advance.
```auto
require 'dry-validation' #v0.11.0
form = Dry::Validation.Form do
configure do
def not_blank?(value)
!blank?(value)
end
def blank?(value)
value.is_a?(String) && value.strip.empty?
end
def self.messages
super.merge(
en: { errors: { not_blank?: 'cannot be blank' } }
)
end
end
required(:name_one) { str? & not_blank? }
required(:name_two).filled(:str?, :not_blank?)
required(:name_three) { str? & (str? > not_blank?) }
end
puts form.call(name_one: 1, name_two: 2, name_three: 3).messages
# => {:name_one=>["must be a string", "cannot be blank"], :name_two=>["must be a string", "cannot be blank"], :name_three=>["must be a string", "cannot be blank"]}
```
---
### Author:  [@smaximov](https://discourse.dry-rb.org/u/smaximov)
#### Post date: [October 12, 2017, 10:38am UTC](https://discourse.dry-rb.org/t/how-to-perform-checks-based-on-the-result-of-the-previous-check/340/2 "2017-10-12T10:38:35Z")
> [@bethesque](#):
>
> Is there a way to short circuit the checking, so that not\_blank? is only checked if str?
In fact, the checks _are_ short-circuit, and if one check fails the rest are skipped. To understand why you are getting extra messages you need to understand what kinds of error messages `dry-validation` has. It is described [here](http://dry-rb.org/gems/dry-validation/basics/working-with-schemas/), but I will give you a summary:
- `errors`: messages which are the result of failing predicates;
- `hints`: messages for predicates which _weren’t evaluated_ because an earlier predicate had failed;
- `messages`: `errors` and `hints` combined.
So what you need is to use `Dry::Validation::Result#errors` instead of `Dry::Validation::Result#messages` as you don’t need hints.
Here’s an example:
```ruby
require 'bundler/inline'
gemfile(true) do
source 'https://rubygems.org'
gem 'dry-validation', '~> 0.11.1'
gem 'rspec', require: 'rspec/autorun'
end
module BlankChecker
def self.call(value)
!value.to_s.strip.empty?
end
end
Form = Dry::Validation.Form do
configure do
def not_blank?(value)
# Delegate the check to a helper object because
# frozen form instances cannot be mocked.
BlankChecker.call(value)
end
def self.messages
super.merge(
en: { errors: { not_blank?: 'cannot be blank' } }
)
end
end
required(:name).filled(:str?, :not_blank?)
end
RSpec.describe 'Dry::Validation error messages' do
subject(:result) { Form.(name: name) }
context 'when input is a valid string' do
let(:name) { 'George' }
it "don't have error messages" do
# Blank check is performed:
expect(BlankChecker).to receive(:call).and_return(true)
expect(result.messages).to be_empty
expect(result.errors).to be_empty
expect(result.hints).to be_empty
end
end
context 'when input is a blank string' do
let(:name) { ' ' }
it 'have an error and no hints' do
# Blank check is performed:
expect(BlankChecker).to receive(:call).and_return(false)
expect(result.messages).to eq(name: ['cannot be blank'])
expect(result.errors).to eq(result.messages)
expect(result.hints[:name]).to be_empty
end
end
context 'when input is not a string' do
let(:name) { 0xDEADBABE }
it 'have an error and a hint' do
# Blank check is NOT performed!
expect(BlankChecker).not_to receive(:call)
expect(result.messages[:name]).to eq(result.errors[:name] + result.hints[:name])
expect(result.errors[:name]).to eq(['must be a string'])
expect(result.hints[:name]).to eq(['cannot be blank'])
end
end
end
```
---
### Author:  [@bethesque](https://discourse.dry-rb.org/u/bethesque)
#### Post date: [October 12, 2017, 10:36pm UTC](https://discourse.dry-rb.org/t/how-to-perform-checks-based-on-the-result-of-the-previous-check/340/3 "2017-10-12T22:36:31Z")
That’s awesome, thank you. I had not seen the documentation for that feature.