Provide an immutable parameter to a function that will not cause any changes

Question

Provide an immutable parameter to a function that will not cause any changes

Looking to develop a function named batchUsers, requiring a parameter of type readonly string in order to create a DataLoader. However, when calling the User.findBy function within my batchUsers function, it's causing issues due to conflicting parameter types.

type BatchUser = (ids: readonly string[]) => Promise<User[]>;

const batchUsers:BatchUser = async (ids) => {
  const users = await User.findBy({ id: In(ids) });

  // rearranging the users to match the ids
  const userMap: { [key: string]: User } = {};
  users.forEach((u) => {
    userMap[u.id] = u;
  })
  return ids.map((id) => userMap[id]);
}

export const userLoader = () => new DataLoader<string, User>(batchUsers)

The error message received is:

The type 'readonly string[]' is 'readonly' and cannot be assigned to the mutable type 'string[]'

concerning the ids used in the findBy function.

If I try changing the type definition as follows:

type BatchUser = (ids: string[]) => Promise<User[]>;

Another error arises:

Argument of type 'BatchUser' is not assignable to parameter of type 'BatchLoadFn<string, User>'.
  Types of parameters 'ids' and 'keys' are incompatible.
    The type 'readonly string[]' is 'readonly' and cannot be assigned to the mutable type 'string[]'

This occurs on the final line where the new Dataloader instance is created.

Seeking suggestions on how to resolve this issue.

typescript readonly type-safety dataloader

Answer 1

Answer №1

In order to get this solution to function properly, I relied heavily on the advice given by caTS and followed these steps:

const users = await User.findBy({ id: In(ids as string[]) });

as opposed to

const users = await User.findBy({ id: In(ids) });

Answer 2

In order to get this solution to function properly, I relied heavily on the advice given by caTS and followed these steps:

const users = await User.findBy({ id: In(ids as string[]) });

as opposed to

const users = await User.findBy({ id: In(ids) });

Provide an immutable parameter to a function that will not cause any changes

Answer №1

Similar questions

What is the syntax for creating ES6 arrow functions in TypeScript?

Angular 6 provides a regular expression that specifically targets the removal of any characters that are not numbers and enforces the allowance of

What could be causing my data to undergo alterations when transitioning from a frontend form submission to a backend API?

Unused Angular conditional provider found in final production bundle

In socket.io, the event occurs twice in a row

Angular and RxJS work together to repeat actions even when an HTTP request is only partially successful

Create a placeholder class for the Form Builder group component within an Angular application

Exploring NestJS: Leveraging the @Body() Decorator to Retrieve Request Body Data

Is it possible to apply a style change to several components at once using a single toggle switch

A Vue component library devoid of bundled dependencies or the need for compiling SCSS files

When using ngFor, a conversion from a string literal type to a regular string occurs, resulting in an error that states: "Element implicitly has an 'any' type because an expression of type 'string' cannot be utilized..."

Variations in default export behavior in Webpack when using Typescript versus Javascript

Ways to incorporate extension methods through a "barrel file" - how to do it?

What could be causing the inability to update a newly logged-in user without refreshing the page?

Dependency injection in Angular 2 service not functioning as expected

Shifting Angular Component Declarations to a New Location

In Typescript, an interface is defined where the "id" property is required to be a number, while all other properties must be of

Object autofill - Typescript utilizing Angular 5

Looking for a specific phrase in the data entered by the user

The "void" type cannot be assigned to the type "ObservableInput<{}>"