Null vs undefined for optional values

[krzkaczor]

What's the reasoning for using null for optional values in generated typings?

I feel like lots of folks prefer to use only one type to determine the absence of a value and usually, they settle on undefined.

Is it possible to customize this during generation?

[schickling]

Thanks a lot for raising this issue @krzkaczor! Would you mind sharing some of your application code where you're interacting with the Prisma Client and where you'd prefer to use undefined instead of null?

[krzkaczor]

@schickling:

Building on top of https://github.com/prisma/prisma-examples/blob/prisma2/typescript/rest-express/src/index.ts

const users = await prisma.user.findOne({ where: { id: 1} })

findOne return type is user | null. Whereas I would prefer it to be user | undefined. And of course, I would also want to have undefined in the runtime 😆

[tajnymag]

I'm also in for such change in the api. It makes a lot of sense when working with optional attributes, which can be undefined but not null.

[benatkin]

I think undefined is a better match.

[benatkin]

A well-known js dev weighs in: sindresorhus/meta#7 https://news.ycombinator.com/item?id=24956156

[matthewmueller]

Thanks for the question! In the Prisma Client there's a specific difference between null and undefined.

null is a specific value that's persisted in an SQL database as NULL. If I run:

prisma.user.create({ 
  data: {
    id: 10,
    customer: null
  }
}

The row in an SQL database looks like this:

id	customer
10	NULL

undefined is the absence of any value. That looks like this:

prisma.user.create({ 
  data: {
    id: 10,
    customer: undefined
  }
}

Conceptually that's the same as

prisma.user.create({ 
  data: {
    id: 10
  }
}

This leaves the prisma engine to decide the value, falling back on the @default value.

id	customer
10	'default value'

---

This conceptual difference doesn't show up that often in Javascript libraries, which is why Sindre chose to consolidate the concept. For Prisma, the difference matters. Hope this helps!