Analysis

Validate.js

http://validatejs.org/

• Allowes empty values: undefined, null, '' (also string with spaces only), [], {}; you can change this behaviour
• There is presence validator to disallow empty values
• numericality validator by default converts strings to number
• Custom error messages
• Multiple error formats
• You can not set guaranteed order of validations

//grouped (default)
{
    "username": ["Username can't be blank"],
    "password": ["Password must be at least 6 characters"]
}

//flat
["Username 'nicklas' is not allowed", "Password must be at least 6 characters"]

//detailed
{
    "attribute": "username",
    "value": "nicklas",
    "validator": "exclusion",
    "globalOptions": {
        "format": "detailed"
    },
    "attributes": {
        "username": "nicklas",
        "password": "bad"
    },
    "options": {
        "within": ["nicklas"],
        "message": "'%{value}' is not allowed"
    },
    "error": "Username 'nicklas' is not allowed"
  },
  {...}
}

Ember Validations

https://github.com/DockYard/ember-validations

• Allowes empty if allowBlank for each validators is enabled. Blank values are false
• Presence validates the property has a value that is not null, undefined, or ''

Ruby on Rails

http://guides.rubyonrails.org/active_record_validations.html

• Allowes empty if allow_blank, allow_nil are enabled. Blank values are false, '', ' ' (whitespace string), nil, [], and {}. http://api.rubyonrails.org/v4.2/classes/Object.html#method-i-blank-3F
• Conditional Validation validates :card_number, presence: true, if:/unless: :paid_with_card?
• Custom messages
• You can set order of validations http://guides.rubyonrails.org/v3.2.9/active_record_validations_callbacks.html #6.2

person.errors.messages
 # => {:name=>["can't be blank", "is too short (minimum is 3 characters)"]}

person.errors[:name]
 # => ["can't be blank", "is too short (minimum is 3 characters)"]

Zend Framework 2

http://framework.zend.com/manual/current/en/index.html#zend-validator

• Zend\Validator\NotEmpty validator (you can change behaviour http://framework.zend.com/manual/current/en/modules/zend.validator.not-empty.html#zend-validator-notempty-types)
• Converts string to number
• Translating messages $validator->setTranslator($translate);
• $input->setAllowEmpty(true) to skip validators if value is empty. You can't allow empty values for validators. http://stackoverflow.com/a/14915485, https://github.com/zendframework/zend-inputfilter/blob/master/src/Input.php#L387
• You can specify validators order using array http://framework.zend.com/manual/current/en/modules/zend.validator.validator-chains.html
• Has InputFilter which can filter and/or validate sets of data (it's like transformer) http://framework.zend.com/manual/current/en/modules/zend.input-filter.intro.html
• You can set order of validations http://framework.zend.com/manual/current/en/modules/zend.validator.validator-chains.html

// $validator->isValid($value);
true/false

// $validator->getMessages()
["stringLengthTooShort" => "The string 'word' is too short; it must be at least 8 characters"]

Simfony 2

http://symfony.com/doc/current/book/validation.html

• About empty values

false === $value || (empty($value) && '0' != $value) // here [] is blank
https://github.com/symfony/validator/blob/master/Constraints/NotBlankValidator.php

'' !== $value && null !== $value // here [] is not blank...
https://github.com/symfony/validator/blob/master/Constraints/BlankValidator.php

null === $value || '' === $value
https://github.com/symfony/validator/blob/master/Constraints/LengthValidator.php

null === $value || '' === $value
https://github.com/symfony/validator/blob/master/Constraints/DateValidator.php

null === $value
https://github.com/symfony/validator/blob/master/Constraints/AbstractComparisonValidator.php

• You can set order of validations (not by default) https://github.com/symfony/symfony/issues/3112

// http://api.symfony.com/3.1/Symfony/Component/Validator/ConstraintViolation.html

// $errors = $validator->validate($author);
// (string) $errors; //for debugging
'The violation message'

// $errors
[{
    message: 'The violation message',
    messageTemplate: 'The raw violation message',
    parameters: 'The parameters to substitute in the raw violation message',
    root: 'The value originally passed to the validator',
    propertyPath: 'The property path from the root value to the invalid value',
    invalidValue: 'The invalid value that caused this violation',
    plural: 'The number for determining the plural form when translating the message',
    code: 'The error code of the violation',
    constraint: 'The constraint whose validation caused the violation',
    cause: 'The cause of the violation'
}, {...}]

Bean validation (Java)

http://docs.jboss.org/hibernate/beanvalidation/spec/1.1/api/

• null element is valid for many validators
• You can set order of validations by using validation groups and group sequences.

//returns
{
    value: 'value',
    message: 'message',
    groups: {},
    payload: {}
}

//returns [] in .list validators
[{...}, ...]

GitHub API

Docs: https://developer.github.com/v3/#client-errors

HTTP/1.1 422 Unprocessable Entity
Content-Length: 149

{
  "message": "Validation Failed",
  "errors": [
    {
      "resource": "Issue",
      "field": "title",
      "code": "missing_field"
    }
  ]
}

Google drive API

https://developers.google.com/drive/v3/web/handle-errors

{
  "error": {
    "errors": [
      {
        "domain": "global",
        "reason": "badRequest",
        "message": "Bad Request"
      }
    ],
    "code": 400,
    "message": "Bad Request"
  }
}