Can Apollo Read Partial Fragments from Cache? Here's the Solution!

Discover how to effectively manage cache data in Apollo for incomplete fragments and avoid errors during mutations in your React applications.
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This video is based on the question https://stackoverflow.com/q/66358289/ asked by the user 'Sandy Gifford' ( https://stackoverflow.com/u/1496453/ ) and on the answer https://stackoverflow.com/a/66369237/ provided by the user 'Mikhail Grechka' ( https://stackoverflow.com/u/15152711/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Can Apollo Read Partial Fragments from Cache?

When working with GraphQL and Apollo, developers often face challenges around cache management, especially when it comes to reading fragment data. A common question arises - can Apollo read partial fragments from cache? This question becomes particularly pertinent when you're attempting to optimize mutation responses while ensuring integrity in your application's state.

In this guide, we will address this question and provide a practical solution to reading partial fragments in Apollo. Let’s dive deeper into the problem and explore effective strategies to tackle it.

Understanding the Problem

Let's take a look at a typical scenario: You have a mutation called editPerson that alters the name and/or description of a person identified by an id. The mutation is implemented in a React hook like this:

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

The challenge arises when either the name or description has not been previously queried and consequently does not exist in the cache. The readFragment function, in such cases, tends to return null, leading to potential invariant errors down the line.

The Core Question

Is there a way to read partial fragments from the cache?

This question is critical for maintaining the application's integrity and offering a seamless user experience without exposing errors.

The Solution

Fortunately, there’s a straightforward solution that allows you to circumvent these issues without relying heavily on cache reads. Here’s how to do it:

1. Pass Needed Data Through Arguments

Instead of relying solely on the cache for your optimistic response, you can directly pass any essential data through the arguments of your useEditPerson function. This way, you'll no longer depend on the gqlClient for reading fragments.

Example Implementation

Here’s a revised version of your useEditPerson hook:

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

Benefits of This Approach

Avoids Null Values: By directly utilizing the data passed as an argument, you prevent the potential of receiving null values, thus ensuring that you don’t run into invariant errors.

Simplicity: This approach simplifies your logic, allowing you to manage state more effectively. You don’t have to handle the complexity of reading fragments from the cache.

Conclusion

In summary, while Apollo Client does not natively support reading partial fragments from the cache, you can efficiently manage raw data through your function's parameters instead. Adapting your implementation this way can help you build more resilient applications that gracefully handle incomplete state without introducing errors.

By implementing the proposed method, you narrow down the risks involved with cache reads, leading to a smoother development experience and a better user interface.

Feel free to share your experiences and any additional solutions in the comment section below!

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