# Ensure that an key is present in tandem with an other keys depending on its value

**URL:** <https://discourse.dry-rb.org/t/ensure-that-an-key-is-present-in-tandem-with-an-other-keys-depending-on-its-value/95>\
**Category:** dry-validation\
**Created:** [August 10, 2016, 1:29pm UTC](https://discourse.dry-rb.org/t/ensure-that-an-key-is-present-in-tandem-with-an-other-keys-depending-on-its-value/95 "2016-08-10T13:29:08Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![erikpaperik](https://avatars.discourse-cdn.com/v4/letter/e/35a633/32.png) [@erikpaperik](https://discourse.dry-rb.org/u/erikpaperik)\
**Post date:** [August 10, 2016, 1:29pm UTC](https://discourse.dry-rb.org/t/ensure-that-an-key-is-present-in-tandem-with-an-other-keys-depending-on-its-value/95/1 "2016-08-10T13:29:08Z")

</div>

Hey,

I have two optional keys `key1` and `key2` in my schema.

If this keys are present, both have to occur as a combination of either two `integer` or two `nil` values.

Supplying only one key is not valid.

How to ensure this with dry-validation?

I tried it with the schema blow … without success.

```ruby
schema = Dry::Validation.Schema do
  optional(:key1).maybe(:int?)
  optional(:key2).maybe(:int?)
  rule(keys_occur_together: [:key1, :key2]) do |k1, k2|
    (k1.none? & k2.none?) | (k1.filled? & k2.filled?)
  end
end

# ++ OK because both values are nil
schema.call({key1: nil, key2: nil})
# ++ OK because both values are integers
schema.call({key1: 123, key2: 1234})

# Should raise an error because key2 is missing - but it doesn't work
schema.call({key1: nil})
# Should raise an error because key1 is missing - but it doesn't work
schema.call({key2: nil})

```

I’m currently struggling with the `nil` values.

If one of the keys it explicitly set to `nil` and the other one is not present, both are considered to be `nil`, which is not true.

---

<div class="post-metadata">

**Author:** ![ggriffin](https://avatars.discourse-cdn.com/v4/letter/g/94ad74/32.png) [@ggriffin](https://discourse.dry-rb.org/u/ggriffin)\
**Post date:** [October 24, 2016, 8:46pm UTC](https://discourse.dry-rb.org/t/ensure-that-an-key-is-present-in-tandem-with-an-other-keys-depending-on-its-value/95/2 "2016-10-24T20:46:19Z")

</div>

`none?` is a [check for nil](http://dry-rb.org/gems/dry-validation/basics/built-in-predicates/), which both key1 and key2 are in your last two test cases. We can see they are both `nil` here:

```auto
    h = {key1: nil}
     => {:key1 => nil} 
    h[:key1]
     => nil 
    h[:key2]
     => nil 
    h[:key1] == h[:key2]
     => true 
    h[:key1].equal?(h[:key2])
     => true

```

Supplying either value produces an error as expected:

```auto
schema.call({key1: 1})
 => #<Dry::Validation::Result output={:key1=>1} errors={:keys_occur_together=>["cannot be defined or must be filled"]}> 
schema.call({key2: 2})
 => #<Dry::Validation::Result output={:key2=>2} errors={:keys_occur_together=>["cannot be defined or must be filled"]}>

```