Hash Validator

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Ruby library to validate hashes (Hash) against user-defined requirements


Add this line to your application's Gemfile:

gem 'hash_validator'

And then execute:

$ bundle

Or install it yourself as:

$ gem install hash_validator


# Validations hash
validations = {
  user: {
    first_name: String,
    last_name:  'string',
    age:        'numeric',
    likes:      'array'

# Hash to validate
hash = {
  foo: 1,
  bar: 'baz',
  user: {
    first_name: 'James',
    last_name:  12345

validator = HashValidator.validate(hash, validations)

  # => false

  # {
      :user => {
          :last_name => "string required",
                :age => "numeric required",
              :likes => "array required"


Define a validation hash which will be used to validate. This has can be nested as deeply as required using the following values to validate specific value types:

  • array
  • boolean
  • complex
  • enumerable
  • float
  • integer
  • numeric
  • range
  • rational
  • regexp
  • string
  • symbol
  • time
  • required: just requires any value to be present for the designated key.
  • hashes are validates by nesting validations, or if just the presence of a hash is required {} can be used.

On top of the pre-defined simple types, classes can be used directly (e.g. String) to validate the presence of a value of a desired class.

Additional validations exist to validate beyond simple typing, such as:

  • An Enumerable instance: validates that the value is contained within the supplied enumerable.
  • A lambda/Proc instance: validates that the lambda/proc returns true when the value is supplied (lambdas must accept only one argument).
  • A regexp instance: validates that the regex returns a match when the value is supplied (Regexp#match(value) is not nil).
  • email: email address validation (string + email address).

Example use-cases include Ruby APIs (I'm currently using it in a Rails API that I'm building for better error responses to developers).

Custom validations

Allows custom defined validations (must inherit from HashValidator::Validator::Base). Example:

# Define our custom validator
class HashValidator::Validator::OddValidator < HashValidator::Validator::Base
  def initialize
    super('odd')  # The name of the validator

  def validate(key, value, validations, errors)
    unless value.is_a?(Integer) && value.odd?
      errors[key] = presence_error_message

# Add the validator

# Now the validator can be used! e.g.
validator = HashValidator.validate({ age: 27 }, { age: 'odd' })
validator.valid?  # => true
validator.errors  # => {}

Multiple validators

Multiple validators can be applied to a single key, e.g.

  { foo: 73 },
  { foo: HashValidator.multiple('numeric', 1..100) }

This is particularly useful when defining custom validators.


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request