# Dry-validation: validate optional parameter dependent on the value of another?

**URL:** https://discourse.dry-rb.org/t/dry-validation-validate-optional-parameter-dependent-on-the-value-of-another/1141
**Category:** dry-validation
**Created:** [October 2, 2020, 7:57pm UTC](https://discourse.dry-rb.org/t/dry-validation-validate-optional-parameter-dependent-on-the-value-of-another/1141 "2020-10-02T19:57:49Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![andreimoment](https://yyz1.discourse-cdn.com/flex031/user_avatar/discourse.dry-rb.org/andreimoment/32/555_2.png) [@andreimoment](https://discourse.dry-rb.org/u/andreimoment)
#### Post date: [October 2, 2020, 7:57pm UTC](https://discourse.dry-rb.org/t/dry-validation-validate-optional-parameter-dependent-on-the-value-of-another/1141/1 "2020-10-02T19:57:49Z")

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I am hoping to validate the integrity of the data structure below, where the `event_key` entry is necessary only for `event_kind` of `conference`

```
data = {"event_info"=>
          {"event_kind"=>"conference", # when 'conference', the event_key is required.
           "event_id"=>"1234567",
           "event_key"=>"123456789012345678901234567890AB" # required for "conference" type events
         }}

```

The validation contains a rule on the optional `event_key` which rule does not run in the absence of the optional key:

```
class EventSettingsContract < Dry::Validation::Contract

  params do
    optional(:event_info).hash do
      required(:event_kind).value(included_in?: ['webinar', 'conference'])
      required(:event_id).value(:string, format?: /\A[0-9]{7}\z/)
      optional(:event_key).value(:string, format?: /\A[A-Z0-9]{32}\z/)
    end
  end
 
  # this doesn't run when event_key is missing
  rule(event_info: [:event_key, :event_id]) do
    key.failure 'event_key must be present for conferences' if values[:event_kind] == 'conference' && values[:event_key].nil?
  end

end

```

When run with the `event_key` definition commented out from the data hash:

```
result = EventSettingsContract.new.call data
=> #<Dry::Validation::Result{:event_info=>{:event_kind=>"conference", 
    :event_id=>"1234567"}} errors={}>

```

When run with the `event_key` included:

```
=> #<Dry::Validation::Result{:event_info=>{:event_kind=>"conference", 
:event_id=>"1234567", :event_key=>"123456789012345678901234567890AB"}} errors={}>

```

All of this is as per documentation. Seems like it is impossible, by design, to run a rule on an optional parameter and check for its presence or absence?

How can I validate the presence of the optional `event_key` parameter when and only when `event_kind` is `conference`?

---

<div class="post-metadata">

### Author: ![andreimoment](https://yyz1.discourse-cdn.com/flex031/user_avatar/discourse.dry-rb.org/andreimoment/32/555_2.png) [@andreimoment](https://discourse.dry-rb.org/u/andreimoment)
#### Post date: [October 2, 2020, 10:04pm UTC](https://discourse.dry-rb.org/t/dry-validation-validate-optional-parameter-dependent-on-the-value-of-another/1141/2 "2020-10-02T22:04:49Z")

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I found an error in my addressing the values in the rule. This fixed the issue:

```
  rule(event_info: [:event_kind, :event_key]) do
    if values[:event_info]
      key.failure "event_key must be present for conferences" if values[:event_info][:event_kind] == 'conference' && values[:event_info][:event_key].nil?
    end
  end
```

---

<div class="post-metadata">

### Author: ![solnic](https://yyz1.discourse-cdn.com/flex031/user_avatar/discourse.dry-rb.org/solnic/32/779_2.png) [@solnic](https://discourse.dry-rb.org/u/solnic)
#### Post date: [November 18, 2020, 8:49pm UTC](https://discourse.dry-rb.org/t/dry-validation-validate-optional-parameter-dependent-on-the-value-of-another/1141/3 "2020-11-18T20:49:45Z")

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@andreimoment you can do `rule(:event_info) ... ` and just check if both `event_kind` and `event_key` are valid and then apply your extra, conditional check. In the future (probably in 2.0.0, maybe earlier), there will be a nice feature based on pattern-matched values so that use cases like your will be simpler to handle.

ps. sorry for late reply

---

<div class="post-metadata">

### Author: ![andreimoment](https://yyz1.discourse-cdn.com/flex031/user_avatar/discourse.dry-rb.org/andreimoment/32/555_2.png) [@andreimoment](https://discourse.dry-rb.org/u/andreimoment)
#### Post date: [November 19, 2020, 9:59pm UTC](https://discourse.dry-rb.org/t/dry-validation-validate-optional-parameter-dependent-on-the-value-of-another/1141/4 "2020-11-19T21:59:40Z")

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Thank you! Hope you’re doing well.