Building Powerful Expo React Native Apps with React Query

Introduction

Building mobile applications with React Native is a popular choice for developers seeking a smooth transition from web development to mobile. However, managing data fetching and state updates can quickly become complex. This is where React Query comes into play.

React Query is a powerful data fetching and caching library that simplifies the process of handling data within your React Native application. It eliminates the need for manual state management and provides a consistent and efficient way to interact with APIs.

In this comprehensive guide, we will explore how to set up an Expo React Native project and integrate React Query to create a robust and performant data-driven app.

Why React Query for Expo React Native?

There are several reasons why React Query is the ideal choice for your Expo React Native projects:

Simplified Data Fetching: React Query takes care of the complex tasks involved in fetching data from APIs, including automatic caching, re-fetching, and error handling.
Efficient Data Management: It automatically manages the state of your fetched data, ensuring your components always display the most up-to-date information.
Improved Performance: React Query optimizes data fetching by caching responses and prioritizing requests, reducing unnecessary network calls and improving application speed.
Enhanced User Experience: By providing a seamless and reactive data experience, React Query helps create more engaging and responsive applications.
Easy Integration with Expo: React Query seamlessly integrates with Expo's ecosystem, making it easy to add its capabilities to your existing Expo project.

Setting Up Your Expo React Native Project

Let's get started by creating a new Expo project and installing the necessary dependencies:

npx create-expo-app my-react-query-app
cd my-react-query-app
npx expo install react-query

This will create a new Expo project, install React Query, and set up the necessary dependencies.

Exploring the Fundamentals of React Query

React Query is built on the concept of queries. A query represents a request for data from an API or a local data source. It's defined using the useQuery hook provided by the library.

Let's break down the essential components of a React Query query:

Query Key: A unique identifier for your query. This helps React Query differentiate between different data requests.
Query Function: A function that fetches the data. It typically makes a network request to your API.
Data Transformer (Optional): A function that transforms the raw data retrieved from the API into a format suitable for your application.
Options (Optional): Allows you to configure various aspects of the query, such as caching behavior, re-fetching strategies, and error handling.

Building a Simple Data Fetching Example

Now, let's create a simple example to demonstrate how to use React Query to fetch data from an API.

1. Create a Data Fetching Component:

// src/screens/ProductsScreen.js
import React from "react";
import { View, Text, FlatList } from "react-native";
import { useQuery } from "react-query";

const fetchProducts = async () =&gt; {
  const response = await fetch("https://fakestoreapi.com/products");
  return response.json();
};

const ProductsScreen = () =&gt; {
  const { isLoading, error, data } = useQuery("products", fetchProducts);

  if (isLoading) {
    return
<text>
 Loading products...
</text>
;
  }

  if (error) {
    return
<text>
 Error fetching products: {error.message}
</text>
;
  }

  return (
<view>
 <flatlist =="" data="{data}" keyextractor="{(item)">
  item.id.toString()}
        renderItem={({ item }) =&gt; (
  <view>
   <text>
    {item.title}
   </text>
   <text>
    {item.price}
   </text>
  </view>
  )}
      /&gt;
 </flatlist>
</view>
);
};

export default ProductsScreen;

In this example, we define a fetchProducts function that retrieves product data from the fakestoreapi.com API. The useQuery hook is used to fetch the data and manage the loading and error states.

2. Integrate the Component into Your Navigation:

// App.js
import React from "react";
import { NavigationContainer } from "@react-navigation/native";
import { createNativeStackNavigator } from "@react-navigation/native-stack";
import ProductsScreen from "./src/screens/ProductsScreen";

const Stack = createNativeStackNavigator();

const App = () =&gt; {
  return (
<navigationcontainer>
 <stack.navigator>
  <stack.screen component="{ProductsScreen}" name="Products">
  </stack.screen>
 </stack.navigator>
</navigationcontainer>
);
};

export default App;

Now, when you run your Expo app, you should see a list of products loaded from the API.

Understanding the Power of Caching

One of the key benefits of React Query is its caching mechanism. When you fetch data with useQuery, React Query automatically caches the response. This means subsequent requests for the same data will be served from the cache, improving performance and reducing network calls.

React Query's caching strategy can be further customized through options:

staleTime: Specifies the time (in milliseconds) after which cached data is considered stale.
cacheTime: Determines the time (in milliseconds) for which cached data should be kept.
refetchOnWindowFocus: Indicates whether the query should be re-fetched when the browser window or application gains focus.

Let's enhance our previous example to demonstrate caching:

// src/screens/ProductsScreen.js
import React from "react";
import { View, Text, FlatList } from "react-native";
import { useQuery } from "react-query";

const fetchProducts = async () =&gt; {
  const response = await fetch("https://fakestoreapi.com/products");
  return response.json();
};

const ProductsScreen = () =&gt; {
  const { isLoading, error, data, refetch } = useQuery("products", fetchProducts, {
    staleTime: 10000, // Cache for 10 seconds
  });

  if (isLoading) {
    return
<text>
 Loading products...
</text>
;
  }

  if (error) {
    return
<text>
 Error fetching products: {error.message}
</text>
;
  }

  return (
<view>
 <flatlist =="" data="{data}" keyextractor="{(item)">
  item.id.toString()}
        renderItem={({ item }) =&gt; (
  <view>
   <text>
    {item.title}
   </text>
   <text>
    {item.price}
   </text>
  </view>
  )}
      /&gt;
  <button onpress="{refetch}" title="Refresh Products">
  </button>
 </flatlist>
</view>
);
};

export default ProductsScreen;

In this updated code, we set staleTime to 10000 milliseconds. After 10 seconds, the cached data will be considered stale, and a new fetch will be triggered when the component is re-rendered. We also added a "Refresh Products" button that calls the refetch function to manually update the data.

Handling Mutations and Updates

React Query is not only for fetching data; it also provides powerful tools for managing mutations and updates. The useMutation hook enables you to perform actions that modify data, such as creating, updating, or deleting records.

Let's add functionality to add new products to our application using useMutation:

// src/screens/ProductsScreen.js
import React, { useState } from "react";
import { View, Text, FlatList, TextInput, Button } from "react-native";
import { useQuery, useMutation } from "react-query";

const fetchProducts = async () =&gt; {
  const response = await fetch("https://fakestoreapi.com/products");
  return response.json();
};

const addProduct = async (newProduct) =&gt; {
  const response = await fetch("https://fakestoreapi.com/products", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify(newProduct),
  });
  return response.json();
};

const ProductsScreen = () =&gt; {
  const { isLoading, error, data, refetch } = useQuery("products", fetchProducts, {
    staleTime: 10000,
  });
  const [newProductTitle, setNewProductTitle] = useState("");

  const { mutate: addNewProduct, isLoading: isAdding } = useMutation(
    addProduct,
    {
      onSuccess: () =&gt; {
        refetch();
        setNewProductTitle("");
      },
    }
  );

  if (isLoading) {
    return
<text>
 Loading products...
</text>
;
  }

  if (error) {
    return
<text>
 Error fetching products: {error.message}
</text>
;
  }

  return (
<view>
 <textinput onchangetext="{setNewProductTitle}" placeholder="Enter product title" value="{newProductTitle}">
 </textinput>
 <button =="" disabled="{isAdding}" onpress="{()" title="Add Product">
  addNewProduct({
            title: newProductTitle,
            price: 10, // Set a default price for demonstration
            description: "New product", // Set a default description
            category: "electronics", // Set a default category
            image:
              "https://fakestoreapi.com/img/products/placeholder.png", // Set a placeholder image
          })
        }
      /&gt;
  <flatlist =="" data="{data}" keyextractor="{(item)">
   item.id.toString()}
        renderItem={({ item }) =&gt; (
   <view>
    <text>
     {item.title}
    </text>
    <text>
     {item.price}
    </text>
   </view>
   )}
      /&gt;
  </flatlist>
 </button>
</view>
);
};

export default ProductsScreen;

In this updated example, we added a addProduct mutation and a text input field for entering a product title. The useMutation hook is used to handle the API call and update the product list after successful insertion.

Handling Errors and Optimizations

React Query provides powerful tools for error handling and optimization to enhance the user experience:

Error Handling: The useQuery hook exposes an error property that holds any error encountered during data fetching. You can use this to display appropriate error messages to the user.
Error Boundaries: React Query automatically handles errors, preventing them from crashing your application. It also provides a mechanism to retry failed requests.
Optimistic Updates: You can update your UI optimistically before the mutation request completes, providing a more responsive user experience.
Query Invalidation: React Query provides ways to invalidate queries manually, ensuring data is refreshed when needed.

Best Practices for React Query in Expo React Native

To maximize the benefits of React Query in your Expo React Native projects, follow these best practices:

Use Unique Query Keys: Ensure every query has a unique key to avoid conflicts and ensure accurate data management.
Define Query Functions: Keep your data fetching logic encapsulated within query functions for better code organization and reusability.
Utilize Caching Strategies: Leverage caching options to optimize data fetching and improve performance.
Implement Error Handling: Thoroughly handle errors to provide a robust and user-friendly experience.
Consider Optimistic Updates: Optimize user experience by implementing optimistic updates for mutations.
Use Query Invalidation Effectively: Invalidate queries when necessary to ensure data consistency.
Optimize for Large Datasets: React Query offers features like pagination and infiniteQueries to handle large data sets efficiently.

Conclusion

React Query is a powerful and essential tool for building data-driven Expo React Native applications. It simplifies data fetching, enhances performance, and provides a streamlined approach to data management.

By embracing the concepts discussed in this guide, you can leverage React Query's capabilities to create robust, efficient, and engaging mobile experiences.

Remember to explore the extensive documentation and community resources available for React Query to unlock its full potential. Happy coding!

How to Set Up an Expo React Native Project with React Query