Solving the useQuery Hook Error: A Guide to Using Apollo's useLazyQuery in React

Discover how to properly use the `useQuery` and `useLazyQuery` hooks from Apollo in your React applications. Learn how to avoid common errors and improve your data fetching logic.
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Understanding the useQuery Hook Error in React with Apollo

When working with React and Apollo, you may encounter a frustrating error while trying to implement the useQuery hook. You might find that it behaves differently from the useMutation hook, leading to confusion. This guide aims to clarify the issue and guide you to the right solution.

The Problem: Mistaken Usage of useQuery

In your function useChannel, you've successfully used the useMutation hook to handle GraphQL mutations. The syntax looks something like this:

[[See Video to Reveal this Text or Code Snippet]]

However, when attempting to apply the same pattern to useQuery, you encounter the error:
TypeError: useQuery is not a function or its return value is not iterable.

The problematic code looks like this:

[[See Video to Reveal this Text or Code Snippet]]

Why Does This Happen?

The key difference between useQuery and useMutation lies in how they return their values:

useQuery is called immediately when the component renders. It returns an object containing the loading status, error message, and the fetched data, but not an array that can be destructured like useMutation.

useMutation, on the other hand, returns an array that includes the mutation function itself, which allows for its destructuring as you've done above.

The Solution: Using useLazyQuery

To properly implement functionality similar to useMutation, you can utilize Apollo's useLazyQuery. This hook allows you to defer the execution of a query until it is triggered by a specific event, much like a mutation.

How to Implement useLazyQuery

With useLazyQuery, you can store it in a variable and invoke it later. Here's how to set it up in your code:

Import useLazyQuery: Ensure you have the hook imported from Apollo's React library.

[[See Video to Reveal this Text or Code Snippet]]

Declare the Lazy Query:
Replace your useQuery line with useLazyQuery like this:

[[See Video to Reveal this Text or Code Snippet]]

Invoke the Query in a Callback:
Now you can call loadFeedProcess whenever you need to fetch the data:

[[See Video to Reveal this Text or Code Snippet]]

Additional Tips

Manage the Response: The response from useLazyQuery is handled similarly to useQuery, where you need to check loading, error, and access data accordingly.

Remember React Hooks Rules: Always call hooks at the top level of your component or custom hook to ensure consistent behavior across renders.

Conclusion

By understanding the fundamental differences between useQuery and useMutation, and leveraging useLazyQuery for deferred data fetching, you can effectively resolve the error you encountered. This allows you to structure your GraphQL queries in a way that's similar to how you'd handle mutations, enhancing your code's clarity and functionality. Now, you can confidently work with Apollo's hooks and avoid common pitfalls in your React applications!