How to getting old data in react query？

React Query is a powerful data synchronization library designed for fetching, caching, and updating data from the server within React applications. It provides tools for handling backend data fetching and caching, including the management of historical data.

In React Query, you can access historical data through several methods:

1. Using keepPreviousData Option

The useQuery hook includes a configuration option keepPreviousData, which retains the previous data while a new query is executed. This option is particularly useful in paginated queries or list filtering scenarios, as it allows users to view the previous data during new data loading, preventing layout shifts and blank screens for a smoother user experience.

For example, if you are implementing a paginated list:

jsx
const { data, isFetching } = useQuery(
  ['projects', page], // Here, "page" denotes the current page number
  fetchProjectList, // A function that calls the API to fetch data
  { keepPreviousData: true }
);

// You can use `data` in your UI to display the previous data until new data is fetched.

2. Accessing the Query Cache

React Query includes a Query Cache that stores the results of all queries. To manually access this cache, you can use the queryCache object, enabling you to retrieve previous data even after initiating a new query.

javascript
import { useQuery, useQueryClient } from 'react-query';

const queryClient = useQueryClient();

const { data } = useQuery('todos', fetchTodos);

// You can retrieve cached data using queryClient
const previousTodos = queryClient.getQueryData('todos');

3. Using onSuccess and onError Callbacks

Both the useQuery and useMutation hooks accept onSuccess and onError callback functions. You can leverage these callbacks for specific logic, such as retrieving previous data upon query success or failure.

jsx
useQuery(
  'todo',
  fetchTodo,
  {
    onSuccess: (newData) => {
      // Handle success, potentially comparing with previous data
    },
    onError: (error) => {
      // Handle errors
    },
  }
);

4. Using useQueryClient Hook's getQueryData Method

You can also use the useQueryClient hook to obtain the queryClient instance and utilize its getQueryData method to fetch data for specific queries, as demonstrated in the previous example.

5. Implementing State History

React Query does not natively support state history, but you can implement it manually by maintaining a state history array within the onSuccess callback. Each time a query successfully returns new data, you can append it to your state history array.

jsx
const [dataHistory, setDataHistory] = useState([]);

const { data } = useQuery('todos', fetchTodos, {
  onSuccess: (newData) => {
    setDataHistory(prevHistory => [...prevHistory, newData]);
  },
});

Summary

By leveraging React Query's keepPreviousData option, manual access to the query cache, and callback functions for success or error, you can effectively manage and retrieve historical data. These methods help you access and utilize historical data to enhance user experience. If you need to maintain a longer-term data history, you may need to implement your own state management logic.