Using Type.Enum or Type.Union does not display information from swagger UI correctly

[cesxhin]

Hi,
I have created an enum schema and would like to give an example of the value.

Type.Object({
      type: Type.Enum(typeUsers, { example: "basic" })
})

As per the image it doesn't even tell me the type of the field.
I also tried using Type.Union with Type.Literal but nothing changed.

I'm using fastify with swagger.

Is there something missing to set?

Thank you,
Cesxhin

[sinclairzx81]

@cesxhin Hi,

TypeBox enums are represented under the type system as a set of as Union values. TypeBox maps enums to the following representation.

const T = { anyOf: [{ const: 'A' }, { const: 'B' }, { const: 'C' }] }

... however for presentation and documentation, most tooling expects enum to represented this way ...

const T = { enum: ['A', 'B', 'C'] }

TypeBox is working towards supporting the second representation but it cannot currently as there are technical challenges supporting two Union-Like representations that describe the same thing. TypeBox chooses the anyOf representation as it is the most general form which unfortunately doesn't render so well in generated OpenAPI documentation.

It is possible to get this type presenting well, but you will need to create a custom type that builds the correct Json Schema representation. The following code does this with the custom type UnionEnum.

https://github.com/sinclairzx81/typebox/blob/master/example/prototypes/union-enum.ts

TypeScript Link Here

import { TypeRegistry, Kind, TSchema, SchemaOptions, Static } from '@sinclair/typebox'

// -------------------------------------------------------------------------------------
// TUnionEnum
// -------------------------------------------------------------------------------------
export interface TUnionEnum<T extends (string | number)[]> extends TSchema {
  [Kind]: 'UnionEnum'
  static: T[number]
  enum: T
}
// -------------------------------------------------------------------------------------
// UnionEnum
// -------------------------------------------------------------------------------------
/** `[Experimental]` Creates a Union type with a `enum` schema representation  */
export function UnionEnum<T extends (string | number)[]>(values: [...T], options: SchemaOptions = {}) {
  function UnionEnumCheck(schema: TUnionEnum<(string | number)[]>, value: unknown) {
    return (typeof value === 'string' || typeof value === 'number') && schema.enum.includes(value)
  }
  if (!TypeRegistry.Has('UnionEnum')) TypeRegistry.Set('UnionEnum', UnionEnumCheck)
  return { ...options, [Kind]: 'UnionEnum', enum: values } as TUnionEnum<T>
}

// ----------------
// Usage
// ----------------

enum Foo { A, B, C }

const E = UnionEnum([Foo.A, Foo.B, Foo.C]) // or UnionEnum(['A', 'B', 'C'])

type E = Static<typeof E>

You can copy / paste this code into your project and use UnionEnum over Enum.

---

As mentioned, TypeBox is working towards a more formal enum representation, but it is taking some time to get integrated due to some of the complexity involved in correctly supporting two Union forms. You can expect an updated Enum type that supports the enum representation sometime later this year.

Hope this helps
S

[cesxhin]

Hi!
Sorry I only found the time to try what you said now.

It only works if the "type" is specified and without specifying an "examples".

 UnionEnum([Foo.A, Foo.B, Foo.C], {type: "string"})
# --- OR ---
[...]
export function UnionEnum<T extends (string | number)[]>(values: [...T], options: SchemaOptions = {}) {
  function UnionEnumCheck(schema: TUnionEnum<(string | number)[]>, value: unknown) {
    return (typeof value === 'string' || typeof value === 'number') && schema.enum.includes(value)
  }
  if (!TypeRegistry.Has('UnionEnum')) TypeRegistry.Set('UnionEnum', UnionEnumCheck)
  return { ...options, [Kind]: 'UnionEnum', enum: values, type: "string" } as TUnionEnum<T>
}

Maybe for convenience I specify the type in SchemaOptions.
For the rest I think it works now.

Thanks a lot!