Joi: Conditional rule based on value of another key

[hueniverse]

[danielb2]

I propose the following syntax:

Example
Requires the presence of another key whenever the value of a key matches the given value.

var schema = {
    a: Joi.string(),
    b: Joi.any().when('a', Joi.string().regex(/^value$/), Joi.required())
};

If the value of a is "value" then b is required. When can take an array of triplets.

[phated]

:+1: I really would love this for schema "tables" /cc @nvcexploder

[hueniverse]

When do you evaluate 'a'? Before or after 'a' itself is evaluated? What if 'a' is '5' and you want it to be a number? should conversion rules apply? This is hard.

[danielb2]

My thought was to evaluate 'a' twice. In the schema itself a: Joi.string() and also in the when case. In the case of when you'd create another schema, i.e.

var schema = {
    a: Joi.string().regex(/^value$/)
};

If that does not return null, then add Joi.required() to b.

[hueniverse]

Add it to b means cloning the entire object at validation time. Very expensive.

[hueniverse]

Partially covered by #260

[phated]

Woot! Thanks!

[danielb2]

Reopening this since the fix didn't address neither #166 nor #188

var Joi = require('joi');

var schema = {
    a: Joi.any().when('b', { is: 5, then: Joi.required(), otherwise: Joi.optional() }),
    b: Joi.any()
};

var thing = {
    b: 5
};
var validate = Joi.validate(thing, schema);

// returns
{
    error: null,
    value: {
        b: 5
    }
}

I expected an error saying that a is required because b is 5

[hueniverse]

@danielb2 Don't do this. Open a new issue next time. In this case, already reported as #334.