incorporate-existing-type-into-zod-schema.md

Incorporate Existing Type Into Zod Schema

Zod's API is great for quickly scaffolding the shape of data that we're working with. This breaks down when data has a more complex shape and is coming from somewhere else, like a Prisma client. The shape of the data, and types provided by the library, are determined somewhere else. We want to leverage that rather than redefine it.

Fortunately, Zod has a way for us to incorporate an existing type into a Zod schema that we're building.

import {z} from 'zod'
import {Book} from '@prisma/client'

const BookOrder = z.object({
  customer: z.object({
    email: z.string().email(),
    name: z.string()
  }),
  books: // how do we use the `Book` type here?
})

We can turn the Book type into a Zod type that we can use in our schema with z.ZodType and z.any.

import {z} from 'zod'
import {Book} from '@prisma/client'

const BookSchema: z.ZodType<Book> = z.any()

const BookOrder = z.object({
  customer: z.object({
    email: z.string().email(),
    name: z.string()
  }),
  books: BookSchema.array()
})

We create a BookSchema with z.any and then narrow it to a z.ZodType with our Book type.

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