Dependent validations for structs

[mohanzhang]

Is it possible to validate one field of a struct depending on the value of another? In particular, I have a startDate and an optional endDate field, and I would like to make sure that endDate is after startDate, if endDate is given.

More specifically, if I do something like

var MyType = t.struct({
  startDate: t.Dat,
  endDate: t.maybe(t.Dat),
  foo: t.Num
});

How can I validate MyType as a whole? It doesn't seem like struct takes a validator function as an argument?

[gcanti]

Is it possible to validate one field of a struct depending on the value of another

Yes, with a subtype:

function isValid(x) {
  if (t.Dat.is(x.endDate)) {
    return x.endDate.getTime() >= x.startDate.getTime();
  }
  return true;
}

var MyType = t.subtype(t.struct({
  startDate: t.Dat,
  endDate: t.maybe(t.Dat),
  foo: t.Num
}), isValid);

console.log(t.validate({startDate: new Date(2015, 10, 30), foo: 1}, MyType).isValid()); // true
console.log(t.validate({startDate: new Date(2015, 10, 20), endDate: new Date(2015, 10, 21), foo: 1}, MyType).isValid()); // true
console.log(t.validate({startDate: new Date(2015, 10, 20), endDate: new Date(2015, 10, 19), foo: 1}, MyType).isValid()); // false

All the the combinators struct, subtype, list, etc... can be composed at your will

[mohanzhang]

Ah, that's brilliant! My next question was going to be how to ensure that the validations get layered so that the original struct's validations also run, but with subtype composition, it happens naturally. Thanks 👍!

[chirag04]

@gcanti instead, i feel like the predicate should have access to the options/context.

eg:

isValidConfirmPassword = (confirmPassword, context) => context.password === confirmPassword;

const ConfirmPassword = t.refinement(t.String, isValidConfirmPassword);

const Person = t.struct({
  name: t.String,
  password: t.String,
  confirmPassword: ConfirmPassword,
}, 'Person');


const formValues = { name: 'a', password: 'b', confirmPassword: 'c' };

validate(formValues, Person, { context: formValues });

Or the predicate could have the same signature as validate. (x, type, path, options)

Person struct can be complex and having to set Person as a refinement on struct and then handle all dependent field in one predicate is not ideal imo. makes sense?