Resolving the Cannot read property 'refetch' of undefined Error in Apollo Client

Описание: Learn how to fix the common error "Cannot read property 'refetch' of undefined" when using Apollo Client with GraphQL queries. Follow our step-by-step guide!
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This video is based on the question https://stackoverflow.com/q/63440165/ asked by the user 'Edgar' ( https://stackoverflow.com/u/12216735/ ) and on the answer https://stackoverflow.com/a/63452793/ provided by the user 'xadm' ( https://stackoverflow.com/u/6124657/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Cannot read property 'refetch' of undefined Error in Apollo Client

If you've ever encountered the error message, "Cannot read property 'refetch' of undefined," while working with Apollo Client in a GraphQL environment, you're not alone. This issue often surfaces when developers attempt to manage the execution of queries and the pending states in their applications. Let's dive into the problem, understand why it occurs, and explore effective solutions to avoid this error in the future.

Understanding the Problem

The error you're seeing typically arises from a misunderstanding in how data is fetched with useQuery() from Apollo Client. In the sample code you shared, the refetch method, which is meant to re-trigger the query, is trying to be accessed when the data is not properly initialized. Here’s a brief look at the original code snippet that generates this error:

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The Key Issues

Unused Query: The skip: true option prevents the query from executing, meaning the variables like data and refetch do not get defined correctly.

Undefined Data: Retrieving refetch from an undefined data can lead to runtime errors when attempting to call refetch().

Solutions to Fix the Error

Now that we understand where the error arises, let’s discuss practical solutions to overcome it:

1. Handling Loading and Data States Appropriately

Rather than attempting to “escape” from undefined data, it’s best to manage your component’s rendering based on the loading state and data availability:

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2. Modify the skip Logic

Using the skip option effectively is crucial. If you want the query to execute based on certain conditions (like user interaction), you can control it with component state:

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

3. Alternative Approach: Use useLazyQuery

If you anticipate needing to manually trigger your query without automatically fetching data when the component mounts, consider using useLazyQuery:

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Conclusion

Resolving the "Cannot read property 'refetch' of undefined" error involves understanding how to manage the loading and execution states of your queries in Apollo Client. By implementing effective state management and considering alternatives like useLazyQuery, you can streamline your Apollo operations and create a more robust application.

By applying the tips shared in this guide, you will not only resolve the error but also enhance your overall understanding of how GraphQL queries work within React components. Happy coding!