JSON-Schema Type and Value Dependencies - json

Question

Is it possible to change a field's schema - according to another's value?
Note: I'm using Ajv
Example using Joi (A non JSON-Schema validator):
const schema = {
a: Joi.valid('x', 'y', 'z'),
b: Joi.string()
.when('a', { is: 'z', then: Joi.string(), otherwise: Joi.number() }),
};

Answer 1

The most direct way would be to have a $ref link depending on a $data pointer. Unfortunately, that isn't supported at the moment.
It's probably cleaner to do it using application logic, but if you're in a situation where you have to use a schema a more verbose way would be using oneOf. In that scenario your schema would be something like:
var ajv = new Ajv({
$data: true
});
let schema = {
oneOf: [
{
title: 'A is Z',
type: 'object',
properties: {
a: {
type: 'string',
enum: ['z']
},
b: {
type: 'string'
}
}
},
{
title: 'A is not Z',
type: 'object',
properties: {
a: {
type: 'string',
not: {
enum: ['z']
}
},
b: {
type: 'number'
}
}
}
]
};
let data = {
a: 'z',
b: '5'
};
ajv.validate(schema, data)
console.log('ERRORS: ', this.ajv.errors)
<script data-require="ajv#*" src="https://cdnjs.cloudflare.com/ajax/libs/ajv/5.3.0/ajv.bundle.js"></script>
EDIT: Since you're using AJV you can also take advantage of the AJV-Keywords module. It has a if / then / else operator that is currently a proposal for adding to the spec.