til/zod/create-union-type-of-nearly-identical-objects.md

Create Union Type Of Nearly Identical Objects

Let's say I have a data layer that can return data in two nearly identical shapes. Either shape has all of the same keys except one has an _id key and the other has a key key. I want a Zod schema that can validate either of these shapes and produce a union type.

Let's start with an intermediate Zod object that holds all possible keys.

const intermediateObject = z.object({
  _id: z.string(),
  key: z.string(),
  name: z.string(),
  age: z.number()
  // any other shared keys
})

I can then manipulate this into the desired schema using or() and omit().

const objectWithoutId = intermediateObject.omit({ _id: true })
const objectWithoutKey = intermediateObject.omit({ key: true })

const unionSchema = objectWithoutId.or(objectWithoutKey)

And this produces the schema and union type I was looking for:

type Union = z.infer<typeof unionSchema>;
/*
type Union = {
    key: string;
    name: string;
    age: number;
} | {
    _id: string;
    name: string;
    age: number;
}
*/

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