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

An alternative way of using Joi.when() that worked for me:

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

.or('a', 'b') prevents a AND b being null (as opposed to '').