Understanding Why queryClient.getQueryData() Returns Undefined in React Query

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The Problem

In your component, you’re trying to use the getQueryData function to retrieve data after saving a new anecdote to your server using useMutation. However, you find that the function returns undefined. Here’s the part of the code you were working with:

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

When you log anecdotes in this piece of code, it results in undefined. This indicates that there's likely an issue with the way React Query is managing your data.

Analysis of the Issue

Upon reviewing your implementation, the problem stems from the keys used for querying. In your App component, you're using the key "notes" when calling the useQuery hook instead of "anecdotes". This mismatch is what leads to getQueryData("anecdotes") returning undefined.

Here's the relevant snippet from your App component:

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

Since you're referencing a different query key, React Query cannot find the corresponding data when you attempt to access it with getQueryData("anecdotes").

The Solution

To fix this issue, you need to ensure that the query keys are consistent across your application. Update the useQuery call in the App component to use the "anecdotes" key.

Step-by-Step Instructions

Open your App component.

Locate the existing useQuery call and change it from:

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

to:

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

Save your changes and re-run your application.

Expected Outcome

By replacing "notes" with "anecdotes", the useQuery hook will correctly manage the fetched data. Consequently, when you call getQueryData("anecdotes") in the mutation's onSuccess callback, you should receive the expected data instead of undefined.

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

Conclusion

Do you have any other questions related to React Query or state management? Feel free to leave a comment below!