Using Joi, require one of two fields to be non empty

Question

If I have two fields, I\'d just like to validate when at least one field is a non empty string, but fail when both fields are empty strings.

Something like this does

Answer 1

If you want to express the dependency between 2 fields without having to repeat all other parts of the object, you could use when:

var schema = Joi.object().keys({
  a: Joi.string().allow(''),
  b: Joi.string().allow('').when('a', { is: '', then: Joi.string() })
}).or('a', 'b');