Typescript Generics for nested array of objects

Question

Hello i am trying to add correct type to object with nested values.

Here is code in sandbox: https://codesandbox.io/s/0tftsf

interface Product {
  name: string,
  id: number
  productList?:ProductItem[]
}

interface ProductItem { 
  color: string, 
  size: number 
 }


type IValidation<T> = {
  field: keyof T
  nestedValidations?: IValidation<
    Pick<
      T,
      {
        [K in keyof T]-?: T[K] extends object ? K : never
      }[keyof T]
      >
    >[] // THIS IS IMPORTANT FOR QUESTION!
  validators?: (any | any | any)[]
}

export async function validateIt<T>(payload: T, validations: IValidation<T>[]): Promise<
  Partial<{
    [key in keyof T]: string[]
  }>
  > { 
    return Promise.resolve(payload);
  }

const product: Product = {
  id: 1,
  name: 'playstation',
  productList: [{
    color: 'red',
    size: 32
    }
  ]
}

const test = validateIt<Product>(product, [
  {
    field: "productList",
    validators: [],
    nestedValidations: [
      {
        field: 'color',
        validators: []
      }
    ]
  }
])

So getting type error and overall i am trying to find correct type for nestedValidations property, which should match interface Product

updated with an idea

Vladimir Štus
– Vladimir Štus

2022-03-23 08:34:30 +00:00
Commented Mar 23, 2022 at 8:34 — Vladimir Štus
– Vladimir Štus, Commented Mar 23, 2022 at 8:34

BorisTB · Accepted Answer · 2022-03-28 10:05:38Z

2

+50

Typescript v3.7 and later

You can achieve this with in keyword in combination with keyof. Basically you're going to "generate" all possible types for each key and typescript will find matching one

type IValidation<T> = T extends Array<infer R> ? IValidation<R> : T extends object ? {
    [K in keyof T]: {
        field: K
        nestedValidations?: IValidation<T[K]>[]
        validators?: (any | any | any)[]
    }
}[keyof T] : never

Playground link

This doesn't work in older typescript versions, because they don't allow recursive types. Link to info.

edited Mar 28, 2022 at 10:05

answered Mar 25, 2022 at 12:07

BorisTB

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5 Comments

Vladimir Štus Over a year ago

Perfect sir own you a beer please vote up! Tnx once again!

Vladimir Štus Over a year ago

I think this is not right since gettng Type alias 'IValidation' circularly references itself error

BorisTB Over a year ago

Thanks, I've added info that this only works with TS versions that support recursive types (3.7+)

Vladimir Štus Over a year ago

tnx, but is there some workaround for older types?

Vladimir Štus Over a year ago

Maybe something like this stackoverflow.com/questions/36966444/…

CKE · Accepted Answer · 2022-03-22 13:59:11Z

0

Maybe I don't see the big picture but I think you want to achieve this:

interface Product {
  name: string,
  id: number
}

type ValueOf<T> = T[keyof T]; // not needed

type IValidation<T> = {
  field: keyof T
  nestedValidations?: IValidation<T>[] // THIS IS IMPORTANT FOR QUESTION!
  validators?: (any | any | any)[]
}

export async function validateIt<T>(payload: T, validations: IValidation<T>[]): Promise<
  Partial<{
    [key in keyof T]: string[]
  }>
  > { 
    return Promise.resolve(payload);
  }

const product: Product = {
  id: 1,
  name: 'playstation'
}

const test = validateIt<Product>(product, [
  {
    field: "id",
    validators: [],
    nestedValidations: [
      {
        field: "name",
        validators: []
      }
    ]
  }
])

Play around here: Typescript Playground

Please note that I had to simplify your data structure since I don't know how 'IRequiredValidator' is defined.

So basically we switch from

nestedValidations?: IValidation<ValueOf<T>>[]

to

nestedValidations?: IValidation<T>[]

because you want to extract the keys of T and not the keys of ( keys of T) Since that would resolve to all the properties of the type of a value assigned to a property of T.

answered Mar 22, 2022 at 13:59

CKE

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5 Comments

Vladimir Štus Over a year ago

No IValidation<T>[] will use just a storeProductImageList key, i need here this part StoreProductImage from export type PostStoreProductPayload = { storeProductImageList?: StoreProductImage[] }

Vladimir Štus Over a year ago

updated with an idea it is close but no cigar

Vladimir Štus Over a year ago

here it is code in sandbox codesandbox.io/s/0tftsf

j1mbl3s Over a year ago

I was playing around with your example and came up with

type IValidation<T, P extends keyof T> = { field: P, validators?: ..., nestedValidations?: IValidation<T[P], keyof T[P]>[]; }

However, there's an issue with trying to define types and validation for types like this: what is a key of a ProductItem[]? 0, 1, 2, ... You should try reapproaching the design with the visitor pattern.

Vladimir Štus Over a year ago

do you have some examples?

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Typescript Generics for nested array of objects

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Typescript v3.7 and later

This doesn't work in older typescript versions, because they don't allow recursive types. Link to info.

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Typescript v3.7 and later

This doesn't work in older typescript versions, because they don't allow recursive types. Link to info.

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