How to throw warning for optional field?

[MubashirWaheed]

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Support plan

• is this issue currently blocking your project? (yes/no): no
• is this issue affecting a production system? (yes/no): no

Context

• node version: v18.12.1
• module version: "^17.7.0"
• environment (e.g. node, browser, native): node
• used with (e.g. hapi application, another framework, standalone, ...): standalone
• any other relevant information:

How can we help?

Basically, I want to throw a warning if an optional field is empty. How can this be achieved?

const Joi = require('joi');

const schema = Joi.object({
    username: Joi.string()
        .alphanum()
        .min(3)
        .max(30)
        .required(),
    birth_year: Joi
        .number()
        .min(2000)
        .warn()
});

console.log({ error, warning, value } = schema.validate({ username: 'abc', birth_year: 1994 }));
console.log({ error, warning, value } = schema.validate({ username: 'abc'}));

Birth year is an optional field and if it is empty how do I throw a warning?

Relevant question on StackOverflow: https://stackoverflow.com/questions/73415737/how-to-make-joi-warning-on-non-existant-property

[Nargonath]

I think if you use anySchema.warning() the warning will always be thrown so you don't have the conditional behaviour you're looking for. Have you tried using a custom validation for that: https://joi.dev/api/?v=17.7.0#anycustommethod-description?