How to Prevent Data Duplication in React Native Fetch Requests

A guide to fixing data duplication issues in React Native when fetching from an API upon refresh.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: React native : fetch keeps duplicating data on each refresh

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Prevent Data Duplication in React Native Fetch Requests

When developing a React Native application, it’s common to encounter various issues related to data fetching. One such issue that many developers face is the duplication of data when the app refreshes, particularly after making changes in the code editor. In this guide, we will discuss a specific case where data fetched from an API duplicates upon refresh and how to resolve it effectively.

The Problem: Data Duplication on Refresh

Imagine you have a React Native app that fetches data from an external API. You have implemented a function to retrieve treatment data, and everything seems to be working fine during the initial render. However, upon refreshing the app after making any changes, the rendered treatment names keep duplicating. For example:

First Render:

laminectomy

prosthesis

After Refresh:

laminectomy

prosthesis

laminectomy

prosthesis

The main question here is: why does the app fail to clear the previous treatments before fetching new data, leading to continuous duplication? Let’s delve into the solution.

The Solution: Clearing State Before Fetching Data

The root of the problem lies in how the state is updated during the data fetching process. In the original code, the treatments are added to the existing state rather than replacing it. This happens because the spread operator (...) is being used, which retains the existing array elements and appends new items to it. To prevent this, you need to set your state properly and clear the previous state before adding new items.

Step-by-Step Solution

Initialize a Temporary Array: Instead of adding each product directly to the treatments state, create a temporary array to store the new treatment items.

Populate the Temporary Array: Loop through the fetched results and push the new treatment items into this temporary array.

Set the State Once: After populating the temporary array, set the treatments state to this array all at once. This way, you avoid merging the old state with the new data.

Here’s how the modified code should look:

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

Why This Works

By setting setTreatments([]) at the beginning, you ensure that the existing treatments are cleared before fetching new data. The temporary array collects all new treatment items first, which are then set to the state in one go. This prevents previously fetched items from persisting, thereby eliminating the issue of duplication seen upon refresh.

Conclusion

In conclusion, preventing data duplication in your React Native app requires careful management of state and how data is fetched from APIs. By clearing the previous state before fetching new data and using a temporary array to set the state, you can maintain a clean and accurate rendering of your data. Make sure to keep these strategies in mind as you develop your applications, and you’ll spend less time battling data issues!