Just a typescript question here... I am using a library called "runtypes" to define all of my item types and to preform runtime validation. They have a feature called "pick" where I can reduce a type down to certain fields. Whenever I get an item from dynamo I want to support sending attribute projection expression to get only the fields I need and I am trying to figure out how to get the return type on the function correct. Here's what I currently have:

import { Record, String } from 'runtypes'

const DynamoItem = Record({
  id: String,
  something: String,
  else: String
})

export const getItem = async (id: string, attributes?: Parameters<typeof DynamoItem.pick>) => {
  const { Item } = await dynamo.get({ id }, { attributes })

  if (!Item) throw new Error('No item')

  return attributes ? DynamoItem.pick(attributes).check(Item) : DynamoItem.check(Item)
}

Currently its always the full "DynamoItem" type even when I call

getItem('myItemId', 'id')

const DynamoItem = Record({
  id: String,
  something: String.optional(),
  else: String.optional()
})

This should help.

That doesn't really solve it just makes me have to manually check if I do actually have a value and that's not what I want.

In that case you’ll have to check the keys and values separately probably.

You needto use a generic here

Hmm that doesnt seem to work either guess I will have to play around a bit see if I can get anything that works

What do you get as a return type there?

I still get the full item, I will try that

The full item as the type?

Yes

Took a look at the library, I can put together an example of how to do this in a bit

Oh thank you 🙂

This isn't exactly right because it uses an any but achieves what you want

Haha yeah this one is wild, thanks for that though I dont really mind using the as any and it does work as expected now. Appreciate the help

Interesting library by the way 👀 What about class-validator, it is easier to use

Classes wouldnt really be possible for parsing incoming data at least not as easy and even then - I really dislike classes unless it's specifically something like SST/CDK resources

you can use class-transformer

I prefer to stay away from using classes in my code functional is just easier and runtypes is really nice and trying to solve the problem like the one in this post would probably be even more annoying using class based components 😅

okay

@thdxr If you ever have time I am back at this again because I have copy pasted the same function over and over for creating a filtered get result from the db and was hoping to not have to do that if possible... I tried this but the return type is { [key: string]: unknown }

import * as Rt from 'runtypes'

const UserItem = Rt.Record({
  name: Rt.String,
  email: Rt.String,
  id: Rt.String
})

type Model = {
  get: (id: unknown, opts: unknown) => Promise<unknown>
}

const UserModel: Model = {
  get: async (id: unknown) => ({ id, name: 'test', email: '<mailto:test@test.com|test@test.com>' })
}

const createFilteredGet = <T extends Rt.Record<{ [key: string]: Rt.Runtype }, false>>(runtype: T, model: Model) => {
  return async <A extends Parameters<typeof runtype.pick>>(id: unknown, attributes?: A) => {
    const item = await model.get(id, { attributes })
    
    if (!item) return null
    
    return attributes ? runtype.pick<A[number]>(...attributes as any).check(item) : runtype.check(item)
  }
}

const getUser = createFilteredGet(UserItem, UserModel)

getUser('1', ['id']).then(item => {
  // item should be typed as { id: string } | null but currently { [key: string]: unknown } | null
  console.log(item)
})