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 not validate

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

When validating against

{a: 'aa', b: ''}

The or condition only tests for the presence of either key a or b, but does test whether the condition for a or b is true. Joi.string() will fail for empty strings.

Here is gist with some test cases to demonstrate

/?gist=84c49d8b81025ce68cfb

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 not validate

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

When validating against

{a: 'aa', b: ''}

The or condition only tests for the presence of either key a or b, but does test whether the condition for a or b is true. Joi.string() will fail for empty strings.

Here is gist with some test cases to demonstrate

http://requirebin.com/?gist=84c49d8b81025ce68cfb

• javascript
• hapi.js
• joi

6 Answers 6

Code below worked for me. I used alternatives because .or is really testing for the existence of keys and what you really wanted was an alternative where you would allow one key or the other to be empty.

var console = require("consoleit");
var Joi = require('joi');

var schema = Joi.alternatives().try(
  Joi.object().keys({
    a: Joi.string().allow(''),
    b: Joi.string()
    }),
  Joi.object().keys({
    a: Joi.string(),
    b: Joi.string().allow('')
    })
);

var tests = [
  // both empty - should fail
  {a: '', b: ''},
  // one not empty - should pass but is FAILING
  {a: 'aa', b: ''},
  // both not empty - should pass
  {a: 'aa', b: 'bb'},
  // one not empty, other key missing - should pass
  {a: 'aa'}
];

for(var i = 0; i < tests.length; i++) {
  console.log(i, Joi.validate(tests[i], schema)['error']);
}

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 '').

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');

You could just use .xor('a', 'b') instead .or('a', 'b'):

var schema = Joi.object().keys({
    a: Joi.string(),
    b: Joi.string()
}).xor('a', 'b');

This allows to be or only a or only b but not both, and not none

if your object is:
{ a: 'non-empty' } or { b: 'non-empty' }
will pass

if your object is:
{ a: '', b: '' } or { a: 'non-empty', b: 'non-empty' } 
will NOT pass

if your object is:
{ a: ''} or { b: '' } 
will NOT pass

if your object is:
{ a: '', b: 'non-empty' } or { a: 'non-empty', b: '' } 
will NOT pass

if your object is:
{ }
will NOT pass

the problem I faced with https://stackoverflow.com/a/61212051/15265372 answer is that if both fields are given you won't face any errors, if you want to fix that you need to replace or with xor.

&. Simply u can use '.and()'

• it will not pass if either one of the fields is empty

var schema = Joi.object().keys({
   a: Joi.string(),
   b: Joi.string()
}).and('a', 'b');````