Type Inference Issue With `useQueries` For Multiple API Calls

by ADMIN 62 views

Introduction

When working with multiple API calls simultaneously using useQueries in TanStack Query, a type inference issue arises. The returned results are inferred as a union type, causing type errors when trying to use the data in the code. In this article, we will delve into the problem, provide a minimal reproducible example, and discuss the expected behavior.

Describe the Bug

When using useQueries to handle multiple API calls simultaneously, the returned results are inferred as a union type (UserResponse | PostsResponse[]). As a result, the data types of each result are not separated, causing type errors when trying to use the data in the code.

Your Minimal, Reproducible Example

import { useQueries } from '@tanstack/react-query';
import { fetchUser, fetchPosts } from './api';

const UserResponse = {
  id: 1,
  name: 'John Doe',
};

const PostsResponse = [
  { id: 1, title: 'Post 1' },
  { id: 2, title: 'Post 2' },
];

const queries = useQueries([
  {
    queryKey: ['user'],
    queryFn: fetchUser,
  },
  {
    queryKey: ['posts'],
    queryFn: fetchPosts,
  },
]);

console.log(queries.map((result) => result.data));

In the above example, fetchUser returns a UserResponse type, and fetchPosts returns a PostsResponse[] type. However, when accessing the data with queries.map((result) => result.data), the returned type is inferred as UserResponse | PostsResponse[], causing type errors.

Steps to Reproduce

  1. Create a component that uses useQueries to handle multiple API calls simultaneously.
  2. Each API call returns different response types. For example, one returns UserResponse type, and another returns PostsResponse[] type.
  3. When accessing the data with results.map((result) => result.data), the returned type is inferred as UserResponse | PostsResponse[], causing type errors.

Expected Behavior

The result of each API call should be clearly separated: user should have the type UserResponse, and posts should have the type PostsResponse[]. Type inference should work correctly, and there should be no issues with type safety.

How Often Does This Bug Happen?

Sometimes

Screenshots or Videos

No response

Platform

React

Tanstack Query Adapter

react-query

TanStack Query Version

v5.62.16

TypeScript Version

v5.5.3

Additional Context

No response

Solution

To resolve this issue, we can use the map function with a type assertion to separate the results of each API call. Here's an updated example:

import { useQueries } from '@tanstack/react-query';
import { fetchUser, fetchPosts } from './api';

const UserResponse = {
  id: 1,
  name: 'John Doe',
};

const PostsResponse = [
  { id: 1, title: 'Post 1' },
  { id: 2, title: 'Post 2' },
];

const queries = useQueries([
  {
    queryKey: ['user'],
    queryFn: fetchUser,
  },
  {
    queryKey: ['posts'],
    queryFn: fetchPosts,
  },
]);

const user = queries[0].data as UserResponse;
const posts = queries[1].data as PostsResponse[];

console.log(user);
console.log(posts);

In this updated example, we use the map function with a type assertion to separate the results of each API call. We access the data property of each result and cast it to the correct type using the as keyword.

Conclusion

Introduction

In our previous article, we discussed the type inference issue with useQueries for multiple API calls. In this article, we will provide a Q&A section to address common questions and concerns related to this issue.

Q: What is the type inference issue with useQueries for multiple API calls?

A: The type inference issue with useQueries for multiple API calls occurs when the returned results are inferred as a union type (UserResponse | PostsResponse[]). This causes type errors when trying to use the data in the code.

Q: What are the common scenarios where this issue occurs?

A: This issue occurs when using useQueries to handle multiple API calls simultaneously, where each API call returns different response types.

Q: How can I resolve this issue?

A: To resolve this issue, you can use the map function with a type assertion to separate the results of each API call. You can also use the as keyword to cast the data to the correct type.

Q: What are the benefits of using useQueries with type assertions?

A: Using useQueries with type assertions provides several benefits, including:

  • Improved type safety: By separating the results of each API call and casting them to the correct type, you can ensure type safety and avoid type errors.
  • Simplified code: Using useQueries with type assertions can simplify your code by reducing the need for complex type checking and casting.
  • Better maintainability: By using useQueries with type assertions, you can make your code more maintainable by reducing the likelihood of type-related errors.

Q: Are there any limitations to using useQueries with type assertions?

A: Yes, there are limitations to using useQueries with type assertions. For example:

  • Increased complexity: Using useQueries with type assertions can add complexity to your code, especially if you have multiple API calls with different response types.
  • Potential errors: If you use the as keyword incorrectly, you may introduce type-related errors into your code.

Q: Can I use useQueries with type assertions in production code?

A: Yes, you can use useQueries with type assertions in production code. However, it's essential to ensure that you use the as keyword correctly and that your code is well-tested to avoid type-related errors.

Q: Are there any alternative solutions to using useQueries with type assertions?

A: Yes, there are alternative solutions to using useQueries with type assertions. For example:

  • Using a separate data structure to store the results of each API call.
  • Using a type-safe library or framework that provides built-in support for handling multiple API calls with different response types.

Conclusion

In conclusion, the type inference issue with useQueries for multiple API calls is a common problem that can be resolved by using the map function with a type assertion. By separating the results of each API call and casting them to correct type, you can ensure type safety and avoid type errors. However, it's essential to be aware of the limitations and potential errors associated with using useQueries with type assertions.