prisma-generator-flavoured-ids

This generator intends to mitigate the issue with weakly-typed IDs on Prisma Schema entities.

Motivation

The following Prisma Schema:

model User {
  id    String  @id @default(uuid())
  name  String
  email String? @unique

  Blogposts Blogpost[]
}

model Blogpost {
  id String @id @default(cuid())

  content String

  Author   User?   @relation(fields: [authorId], references: [id])
  authorId String?
}

will generate the model and methods related to user with id being of type string. This is not ideal, as it is easy to pass the wrong type of ID to the generated methods, e.g.:

// The called of the method passes `userId`
const deleteBlogpostsForUser = async (id: string) => {
  // From within the method, typescript doesn't prevent from using `userId` as a `blogpostId`
  await prisma.blogpost.deleteMany({
    where: { id },
  });
}

A related Prisma issue

Solution

To resolve the problem, the generator will overwrite the resulting types with the following:

1. Add a branded type for each model ID, e.g.

export interface Flavoring<FlavorT> {
  _type?: FlavorT
}
export type Flavor<T, FlavorT> = T & Flavoring<FlavorT>

export type UserId = Flavor<string, 'UserId'>

2. Change the methods to use the branded type, e.g.

export type UserWhereUniqueInput = Prisma.AtLeast<{
  id?: UserId
  /// ...
}>

export type UserWhereInput = Prisma.AtLeast<{
  id?: StringFilter<"User"> | UserId
  /// ...
}>

// and others

In result, the example from above will be prevented by typescript:

import { UserId } from '@prisma/client'

const deleteBlogpostsForUser = async (id: UserId) => {
  await prisma.blogpost.deleteMany({
    // Typescript will show an error here
    where: { id },
  });
}

Disclaimer

1. Ideally, Prisma needs to add native support for branded types. If you find this solution useful, please up-vote the Prisma issue

2. This is a dirty approach, as it relies on the generated code. This library has been used for several months and had to be changed significantly based on the changes Prisma made to its client

Installation and usage

# inside your project's working tree
npm i prisma-generator-flavoured-ids

generator flavoured_ids {
  provider = "prisma-generator-flavoured-ids"
  // A path to the generated client - can vary on your setup
  output   = "node_modules/.prisma/client/index.d.ts"
}