Implementing complex dependency management for optimistic updates

Provide an example of managing complex dependencies in a React application to ensure that optimistic updates do not cause inconsistent state due to interrelated data.

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

function useOptimisticUpdateTodo() {
  const queryClient = useQueryClient();
  const updateTodo = useMutation(editTodo, {
    onMutate: async (updatedTodo) => {
      await queryClient.cancelQueries('todos');
      const previousTodos = queryClient.getQueryData('todos');
      queryClient.setQueryData('todos', old =>
        old.map(todo =>
          todo.id === updatedTodo.id ? { ...todo, ...updatedTodo } : todo
        )
      );
      return { previousTodos };
    },
    onError: (err, newTodo, context) => {
      queryClient.setQueryData('todos', context.previousTodos);
    },
    onSettled: () => {
      queryClient.invalidateQueries('todos');
    },
  });
  return updateTodo;
}

This function uses React Query's useMutation hook to optimistically update a todo item. It leverages the onMutate function to cancel any ongoing fetches and temporarily updates the cache with the new todo data. If the mutation errors out, the onError function reverts to the original todos. The onSettled function ensures that the todos query is refetched to synchronize with the server state, ensuring data consistency even among interrelated data.

function editTodo(updatedTodo) {
  // This function would send the updatedTodo information to your API.
  // Replace with your actual API call logic.
  return fetch('api/todos/update', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(updatedTodo),
  }).then(res => res.json());
}

This helper function simulates an API call to update a todo item. It is meant to be used within the useMutation hook's mutation function. Ensure this is replaced or adapted to match the actual API call structure of your application.