Redux Toolkit Query - Cache Behavior
Tags: react, learning, programming
Published: 2023-10-30 18:16:58

RTK Query revolutionizes data management in Redux by intelligently handling caching strategies, enhancing your application's performance, and reducing redundant network requests. One of its key features is the default cache behavior, which ensures that data fetched from the server is stored in the Redux store, preventing repetitive calls for the same data.

By serializing the parameters used in API requests into a queryCacheKey, RTK Query identifies identical requests. When multiple components request the same data, they share the cached results, eliminating unnecessary network traffic. This efficient default behavior is invaluable, but challenges arise when cached data becomes outdated due to backend operations or errors.

**Problem Description:**

**Scenario**: Application fetches permissions for a user.
**Event**: Backend operation modifies these permissions.
**Issue**: Subsequent request results in a 404 error.
**Importance**: Crucial to update cached data.
**Action**:
 1. Clear the cache for the specific query.
 2. Set data to null to prevent outdated content persistence.

**Objective**: Ensure the cache contains the most recent, accurate information.
**Outcome**: Prevents display of outdated or erroneous data.
**Result**: Enhanced user experience, reliable data presentation.

RTK Query equips developers with methods for manipulating cache behavior. These tools empower you to proactively handle scenarios where cached data should be considered invalid or when refreshing data is necessary. Instead of allowing your application to continue using outdated information, these methods enable you to refresh the cache with accurate data, ensuring a seamless user experience.

Understanding these cache manipulation methods is vital for addressing real-world challenges. By employing these tools effectively, you can guarantee that your application consistently serves the most precise and up-to-date information, even in the face of unexpected errors or backend changes. RTK Query's flexibility and power lie not just in its default cache behavior but also in the control it offers developers to handle dynamic, real-time data scenarios.



## Handling the distinction between data and currentData

It is a subtle yet crucial aspect of managing cache behavior in RTK Query. While the official documentation primarily emphasizes the use of data, it's equally important to recognize the significance of currentData. Here's a detailed guide on how to address this issue effectively:

**Understanding data vs. currentData:**

**data**: Represents the most recent data returned by a query or mutation, whether from the cache or a network request.
**currentData**: Represents the data as of the last successful fetch or query resolution, holding information from the latest successful request.

**Best Practices:**

**Clearing the Cache on Error:**

Whenever an error occurs (e.g., a 404 error), it's essential to clear the cache for the specific query. Set data to null to ensure outdated or incorrect data isn't used.

```
// Example of clearing cache on error
const clearCacheOnError = async (error: Error, { queryFulfilled, updateCacheData }: TClearOnError) => {
  try {
    await queryFulfilled;
  } catch (e) {
    updateCacheData(null);
  }
};
```


**Utilizing currentData:**

Always rely on currentData for rendering or other operations, especially when there's an error and the cache is cleared. currentData provides the most up-to-date and accurate information.


```
// Example of using currentData
const {
  data: permissions,
  currentData: currentPermissions,
  refetch: refetchPermissions,
  isFetching: isFetchingPermissions,
  isLoading: isLoadingPermissions,
} = useModifiedPermissionsQuery({ id });
```

By integrating these practices into your code, you ensure that your application handles errors gracefully and maintains data integrity. Clearing the cache on error and utilizing currentData for rendering not only aligns your application with the most recent data but also enhances the overall user experience.

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## Conclusion:

RTK Query is a valuable tool for managing cached data in Redux. However, a common challenge is the improper handling of cached data, especially when errors occur. To overcome this issue, it’s crucial to clear the cache when errors like 404 occur, using null to ensure outdated data isn't retained. Additionally, favor currentData over data to maintain accuracy after cache clearing. These best practices help ensure your application delivers up-to-date and reliable data to users.


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