RTK Query 2.7.0: Fixing Rehydration With `keys` In State

Aug 14, 2025 by Lucia Rojas 57 views

The "keys" Addition in `state.api.provided` and Rehydration Issues

Hey everyone! Today, we're diving deep into a tricky issue that some of us have encountered with Redux Toolkit (RTK) Query, specifically after the release of version 2.7.0. It revolves around how the keys were added to state.api.provided and how it's causing some rehydration problems. If you've been scratching your head over errors related to cacheKeys not being iterable, you're in the right place.

What's the Buzz About?

So, what exactly happened? In RTK Query's 2.7.0 release, there was a significant restructuring of the state.api.provided data structure. The goal was noble: to create a reverse-mapping between tags and cache keys. This enhancement aimed to drastically improve performance, which sounds fantastic, right? But as often happens in the world of software, this change introduced an unexpected side effect – issues with rehydration.

The official release notes on GitHub highlight this structural change, but they don't explicitly mention the potential rehydration problems. This is where the community's detective work comes in, and that's what we're going to explore today.

The Rehydration Riddle

Rehydration, in simple terms, is the process of restoring your application's state from a persisted storage (like local storage or a cookie). This is crucial for providing a seamless user experience – no one wants to lose their progress every time they refresh the page! With RTK Query, rehydration ensures that your cached data and API responses are restored, so your app can pick up where it left off.

However, the structural changes in version 2.7.0 seem to have thrown a wrench into this process. Some developers, including yours truly, have noticed errors popping up, particularly the dreaded "cacheKeys not being iterable." This error usually surfaces after refreshing the application a couple of times, which is a classic sign of a rehydration issue.

Decoding the Error: "`cacheKeys` not being iterable"

Let's break down this error message. "cacheKeys not being iterable" essentially means that the code is trying to loop through something that isn't an array or a similar iterable structure. In JavaScript, you can iterate over arrays, strings, Maps, Sets, and other iterable objects using loops like for...of or methods like forEach. When you try to use these methods on something that isn't iterable, you get this error.

In the context of RTK Query, cacheKeys is supposed to be a collection of keys that identify cached data. The system uses these keys to manage the cache and ensure that data is properly retrieved and updated. If cacheKeys is not in the expected format (i.e., an iterable), the application can't properly access the cached data, leading to errors.

Tracing the Root Cause

One sharp-eyed developer pinpointed a specific line of code that might be the culprit: [this line in buildSlice.ts](https://github.com/reduxjs/redux-toolkit/blob/d8190e30406025681dd2164605e9cf2ef121e19d/packages/toolkit/src/query/core/buildSlice.ts#L542). This line is located within the buildSlice.ts file, which is a core part of RTK Query's internal workings. The suggestion is that the code might need to go one level deeper into the state structure to correctly access the cacheKeys.

To really understand this, we need to dive into the new structure of state.api.provided. Before version 2.7.0, the structure might have been simpler, perhaps directly listing cache keys. But with the introduction of reverse-mapping for tags, the structure has become more nested. This nesting is what seems to be causing the issue – the code is looking for cacheKeys in the wrong place.

A CodeSandbox to the Rescue

To illustrate this issue and make it easier for others to reproduce and debug, a CodeSandbox was created. You can check it out here: RTK Query Persist Pending Forked. This CodeSandbox provides a minimal, reproducible example of the rehydration problem. By refreshing the example a couple of times, you should be able to trigger the "cacheKeys not being iterable" error.

Using CodeSandbox is incredibly helpful in these situations because it allows developers to share their code and demonstrate issues in a controlled environment. It eliminates the "works on my machine" problem and makes collaboration much smoother. If you're facing this issue, playing around with the CodeSandbox can give you valuable insights.

How to Use the CodeSandbox

Open the CodeSandbox: Click on the link provided above to open the sandbox in your browser.
Explore the Code: Take a look at the code structure. Pay attention to the RTK Query setup, the API endpoints, and the rehydration logic.
Refresh the Preview: Refresh the preview pane a couple of times. This is usually enough to trigger the error.
Inspect the Console: Open your browser's developer console. You should see the "cacheKeys not being iterable" error message, along with a stack trace that points to the problematic code.
Experiment and Debug: Try modifying the code to see if you can fix the issue. You might try adjusting how the state is accessed during rehydration or how the cacheKeys are handled.

Diving Deeper: Understanding `state.api.provided`

To truly grasp the root of the problem, let's delve into what state.api.provided is and how it's structured. In RTK Query, state.api.provided is a crucial part of the internal state management. It keeps track of which API endpoints have provided which tags. This mapping is essential for RTK Query's caching and invalidation mechanisms.

Before Version 2.7.0

Before the 2.7.0 release, the structure of state.api.provided was likely simpler. It might have directly mapped tags to cache keys or used a less nested structure. This simplicity made it easier for the rehydration logic to access the necessary data.

After Version 2.7.0

With the introduction of reverse-mapping, the structure of state.api.provided became more complex. The goal was to efficiently handle scenarios where you need to know which cache entries are associated with a particular tag. This reverse-mapping allows RTK Query to quickly invalidate the correct cache entries when data changes.

The new structure likely involves an additional layer of nesting. Instead of directly listing cache keys, the structure might now look something like this:

{
 tag1: {
 keys: [cacheKey1, cacheKey2],
 },
 tag2: {
 keys: [cacheKey3, cacheKey4],
 },
}

In this example, each tag is associated with an object that contains a keys array. This array holds the cache keys associated with that tag. This structure is more efficient for reverse-mapping, but it also means that the code needs to navigate one level deeper to access the cacheKeys.

Potential Solutions and Workarounds

So, what can we do about this? If you're encountering the "cacheKeys not being iterable" error, here are a few potential solutions and workarounds:

Adjust the Rehydration Logic: The most direct solution is to adjust the rehydration logic to correctly access the cacheKeys in the new structure. This might involve modifying the code that iterates over state.api.provided to go one level deeper.
Pin RTK Query Version: If you need a quick fix and aren't ready to dive into the code, you can pin your RTK Query version to a version before 2.7.0. This will avoid the structural changes and the associated rehydration issues. However, this is a temporary solution, and you'll eventually want to upgrade to the latest version to take advantage of new features and performance improvements.
Contribute to the Discussion: If you have insights or potential solutions, consider contributing to the discussion on the Redux Toolkit GitHub repository. Your input can help the RTK Query maintainers address the issue and release a fix.

Diving into the Code: Adjusting the Rehydration Logic

Let's explore how you might adjust the rehydration logic. The key is to ensure that you're correctly accessing the cacheKeys in the new structure of state.api.provided. If the structure is indeed nested as described above, you'll need to modify your code to iterate over the keys array within each tag.

Here's a simplified example of how you might have been accessing cacheKeys before version 2.7.0:

const providedState = state.api.provided;
for (const cacheKey of providedState) {
 // Process cacheKey
}

And here's how you might need to access them after version 2.7.0:

const providedState = state.api.provided;
for (const tag in providedState) {
 if (providedState.hasOwnProperty(tag)) {
 const tagData = providedState[tag];
 if (tagData && tagData.keys) {
 for (const cacheKey of tagData.keys) {
 // Process cacheKey
 }
 }
 }
}

In this example, we're first iterating over the tags in providedState. For each tag, we're checking if it has a keys property. If it does, we then iterate over the cacheKeys in that array. This ensures that we're correctly accessing the cache keys in the new structure.

The Bigger Picture: Community Collaboration

This issue highlights the importance of community collaboration in software development. When a change like this is introduced, it's the collective effort of developers sharing their experiences, debugging code, and proposing solutions that ultimately leads to a fix. The CodeSandbox example is a perfect illustration of this – it provides a shared platform for developers to investigate and resolve the issue.

If you're facing this problem, don't hesitate to reach out to the Redux Toolkit community. Share your code, describe your symptoms, and ask for help. Chances are, someone else has encountered the same issue and might have a solution or a workaround.

Staying Updated: Monitoring the Redux Toolkit Repository

To stay informed about the progress on this issue and other RTK Query updates, it's a good idea to monitor the Redux Toolkit GitHub repository. You can subscribe to the repository to receive notifications about new releases, bug fixes, and discussions.

The maintainers of Redux Toolkit are very responsive to community feedback, and they actively work to address issues and improve the library. By staying engaged, you can contribute to the development of RTK Query and ensure that it continues to meet your needs.

Final Thoughts: Navigating the Ever-Evolving World of Software

The "keys not being iterable" issue is a reminder that software development is an ever-evolving field. Libraries and frameworks are constantly being updated, and sometimes these updates can introduce unexpected side effects. The key is to stay informed, be proactive in debugging issues, and collaborate with the community.

If you've encountered this issue, I hope this article has provided some clarity and guidance. Remember, you're not alone, and together, we can navigate these challenges and build better applications.

Happy coding, everyone!