How to handle union types in query parameters?

[gloomybrain]

Hey everyone! It seems I've got stuck with Ts.ED query parameter parsing. In particular I have a REST controller that accepts two types of the same query parameter:

• GET foo.bar/entity?createdAt[lte]=2021-12-10T10:10:17.717Z
• GET foo.bar/entity?createdAt=2021-12-10T10:10:17.717Z

The general idea to handle this is to have the following classes defined:

class EntityDto {
  createdAt?: Date | EntityFilter<Date>;
}

class EntityFilter<T> {
  lte?: T;
}

As you can see I have to check whether the createdAt query parameter is a String and then make a Date instance out of it OR createdAt is an Object and I should create an instance of my EntityFilter class with the lte field set to an appropriate Date instance.

So my questions is as follows: what decorators should I use to define such a distinction? And how should my EntityDto class look like given that its createdAt field has to be either a Date or an EntityFilter instance?
I'd highly appreciate any help, and I suppose there might be some solutions other than writing these filters by hand.

[Romakita]

You can try to use the OnDeserialize decorator. It's not possible to automatically deserialize union type.

@OnDeserialize(v => isObject(v) ? {lte: new Date(v.lte)} : new Date(v)) 

See you

[gloomybrain]

@Romakita thanks for the quick response!

Will try this

[gloomybrain]

Worked like charm, thank you again!

For those who are interested: it is still possible to make Ts.ED validate by providing schema-generating decorators, like this:

@AdditionalProperties(false)
class EntityDto {
  @AnyOf(date().format('date-time'), from(EntityDateFilter) // this builds the validation json-schema
  @OnDeserialize(parseDateFilter) // and this performs the actual parsing of a raw query parameters object
  @Optional()
  public createdAt?: Date | EntityDateFilter;
}

@AdditionalProperties(false)
class EntityDateFilter {
  @Format('date-time')
  @Optional()
  gt?: Date; // means '>'
  lt?: Date; // means '<'
}

type RawDateFilter = {
  gt?: string;
  lt?: string;
};

const parseDateFilter = (value: string | RawDateFilter): Date | EntityDateFilter => {
  if (typeof value === 'string') {
    return new Date(value);
  }

  const filter = new EntityDateFilter();
  if (value.gt) {
    filter.gt = new Date(value.gt);
  }

  if (value.lt) {
    filter.lt = new Date(value.lt);
  }

  return filter;
}