Solving the Issue of undefined Results When Using useQuery Multiple Times in React

Discover why you might be receiving `undefined` results when using `useQuery` multiple times in a React application and learn practical solutions to resolve the issue effectively.
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Solving the Issue of undefined Results When Using useQuery Multiple Times in React

When developing applications using React and query management libraries such as Apollo Client, you might encounter situations where trying to fetch data multiple times on a single page results in undefined responses. This can be particularly frustrating, especially when you know that your backend is sending the right data. In this post, we’ll explore why you might be facing this issue and how to fix it so you can successfully load different data seamlessly in your application.

The Problem: Multiple useQuery Calls Leading to undefined Result

Consider the following example where a developer tries to retrieve different sets of data with multiple calls to useQuery:

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

The developer notices that, despite the backend sending the correct response, the front end shows undefined for these variables. This discrepancy can be attributed to several syntax errors in the code that need rectification.

The Solution: Correcting Syntax Errors

Spacing Issues: There should be a space between const and {data... for readability and proper syntax.

Plural Variables: The key for the variable passed to useQuery should be plural i.e., it should be changed from variable to variables. This is important because the function expects this structure to work as intended.

Curly Bracket Validation: Ensure that you’re using the correct curly brackets {{...}} when defining your variables.

Revised Code Example

To address these potential issues, you can modify your code as follows:

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

This revised code will let React's useQuery hook properly interpret the variables passed into it, ensuring you get the desired data output.

What Happens Behind the Scenes

Backend Communication: When you fix the above issues, the request sent to your backend (in this case, a NestJS server) will be structured correctly. The server can respond adequately because it recognizes the queried parameters.

Frontend Rendering: The React component will then successfully receive and render the data received from the backend, ensuring all var1, var2, etc., are populated correctly.

Conclusion

Encountering undefined results from using useQuery multiple times can be attributed to small syntax errors that can easily be overlooked. By ensuring proper syntax and structure in your code, you can significantly enhance the performance and functionality of your React components.

Remember to always check for:

Correct usage of variables instead of variable.

Proper spacing and structure in your queries.

With these adjustments, you should see your data loading correctly in your application. Happy coding!