Joi field validation base on a set of values of another field

Question

I am trying to validate field in an object based on a set of values of another field. Assuming my object has to fields, field1 and field2. Field one can take values A, B, C, D, E, F, H, I. Now say if field1 is any of the values; A, B, C, H, then field2 should be null. How do I do this. I think it should have the synthax below but I don't know how to implement it completely.

const mySchema = Joi.object({
   field1: Joi.string().valid('A','B','C','D','E','F','H','I').required(),
   field2: Joi.when('field1', is: <A or B or C or H> then: <field2 should be null> otherwise: Joi.date().required())
});

NB: I am using "@hapi/joi": "^17.1.1"

Answer 1

I finally got it by trying:

const Joi = require("@hapi/joi");

const schema = Joi.object({
    field1: Joi.string().valid('A', 'B', 'C', 'D', 'E', 'F', 'H', 'I').required(),
    field2: Joi.when('field1', {
        is: Joi.string().valid('A', 'B', 'C', 'H'),
        then: Joi.valid(null),
        otherwise: Joi.date().required(),
    }),
});

const validation = [schema.validate({ field1: 'B', field2: null }), schema.validate({ field1: 'E', field2: null }),
                    schema.validate({ field1: 'E', field2: Date() }), schema.validate({ field1: 'A', field2: Date() })];

validation.forEach((v)=>{
    if(v.error){
        console.log(JSON.stringify(v.error));
    }else{
        console.log(JSON.stringify(v.value));
    }
});

Here is the output.

{"field1":"B","field2":null}
{"_original":{"field1":"E","field2":null},"details":[{"message":"\"field2\" must be a valid date","path":["field2"],"type":"date.base","context":{"label":"field2","value":null,"key":"field2"}}]}
{"field1":"E","field2":"2020-05-20T12:26:48.000Z"}
{"_original":{"field1":"A","field2":"Wed May 20 2020 13:26:48 GMT+0100 (West Africa Standard Time)"},"details":[{"message":"\"field2\" must be [null]","path":["field2"],"type":"any.only","context":{"valids":[null],"label":"field2","value":"Wed May 20 2020 13:26:48 GMT+0100 (West Africa Standard Time)","key":"field2"}}]}