Is there a way omit keys from a discriminated union? Or an alternative way to achieve something similar?

[kculmback-eig]

We're hoping to do something like this:

export const BaseTemplateSchema = z.object({
  id: z.string(),
  name: z.string(),
  lastUpdated: z.string().optional(),
  createdOn: z.string(),
})

export const CommunicationTemplateSchema = BaseTemplateSchema.merge(
  z.object({
    type: z.literal('templates:types:communication'),
    smsTemplate: z.string().optional().nullable(),
    subject: z.string(),
    htmlTemplate: z.string(),
    textTemplate: z.string(),
  })
)

export const NoteTemplateSchema = BaseTemplateSchema.merge(
  z.object({
    type: z.literal('templates:types:note'),
    textTemplate: z.string(),
  })
)

export const TemplateSchema = z.discriminatedUnion('type', [
  CommunicationTemplateSchema,
  NoteTemplateSchema,
])

export const CreateTemplateSchema = TemplateSchema.omit({
  id: true,
  createdOn: true,
  lastUpdated: true,
})

This doesn't work when we get to CreateTemplateSchema because omit does not exist on the ZodDiscriminatedUnion type.

Essentially what we're trying to do is to have a TemplateSchema type that has different keys depending on the type field. But we also want to be able to omit certain keys from the type for certain requests (e.g. you can't provide an id when creating a template).

Is there a way to achieve this with zod? Wether using discriminated unions or something else?

[scotttrinh]

Yeah, we've talked previously about adding the other ZodObject methods to ZodDiscriminatedUnion, but haven't made any progress on that that I'm aware of. The temporary fix is to make a separate union like this:

TypeScript Playground

const createOmits = {
  id: true,
  createdOn: true,
  lastUpdated: true,
} as const;

export const CreateTemplateSchema = z.discriminatedUnion("type", [
  CommunicationTemplateSchema.omit(createOmits),
  NoteTemplateSchema.omit(createOmits),
]);

[kculmback-eig]

Okay, thank you!

[wiese]

Somewhat related: I needed Omit for the type created by z.infer<typeof myDiscriminatedUnion>; and got the removal of some properties working using microsoft/TypeScript#31501 (comment)

[johnsvanda]

Any update for this?

[lukachi]

const MySchema = z.discriminatedUnion('type', [
  z.object({ type: z.literal('example1'), foo: z.string() }),
  z.object({ type: z.literal('example2'), bar: z.number() }),
])

const myNewTypeWithoutEx2: Exclude<
  z.infer<typeof MySchema>,
  { type: 'example2' }
>