---
title: How to validate the presence of a boolean field in a Rails model
teaser: 'A subtle bug happens when validating the presence of boolean fields in Rails.
  Here''s how to find it before it hits production.

  '
tags: testing,ruby,rails
author: Stefanni Brasil
published_on: 2022-12-21
---

There is a subtle bug that happens when validating the presence of boolean fields in Rails. Ensuring adequate test coverage helps us find those issues before they hit production.

## Broken code

Here is an example that looks right but hides a subtle problem:

```ruby
class Question < ApplicationRecord
  validates :required, presence: true
end
```

Here is the spec that describes the behavior we want. We want `required` to be either `true` or `false` but not `nil`. This helps avoid the [Three-state boolean problem].

```ruby
describe "#required" do
  it "only allows true or false" do
    expect(Question.new(required: false)).to be_valid
    expect(Question.new(required: true)).to be_valid
    expect(Question.new(required: nil)).to be_invalid
  end
end
```

But when we run the test, we get an error message:

```
Failure/Error: expect(Question.new(required: false)).to be_valid
  expected #<Question id: nil, required: false, created_at: nil, updated_at: nil> to be valid, but got errors: Required can't be blank
```

Aha! The error message highlights the subtle bug in our implementation. The spec fails because the Rails `presence` validator rejects any falsy values, not just `nil`.

## How to validate the presence of a boolean column in Rails

According to [Rails validations guides], we should use the `inclusion` validator to ensure the `required` boolean field is either `true` or `false`, but not `nil`.

```ruby
class Question < ApplicationRecord
  validates :required, inclusion: [true, false]
end
```

Now, running the spec again, it passes and we avoided getting paged for an incident during the night 🎉

(Thanks, Joël Quenneville, for the great review!).

[Rails validations guides]: https://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html#method-i-validates_presence_of
[Three-state boolean problem]: https://thoughtbot.com/blog/avoid-the-threestate-boolean-problem

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