The Mysterious Case of useMutation Not Firing Rerender in React

Are you stuck in the vortex of frustration, wondering why your React application refuses to rerender when using the useMutation hook from @apollo/client? Fear not, dear developer, for you are not alone in this plight. In this article, we’ll embark on a thrilling adventure to uncover the secrets behind this enigmatic issue and provide you with the solutions to get your application back on track.

The Suspects: Common Causes of the Issue

Before we dive into the solutions, let’s first identify the usual suspects behind this problem. Make sure you’ve checked off these common culprits:

• useMutation is not being called inside a React component: Ensure that the hook is being used within a valid React component, as it relies on the component’s lifecycle to function correctly.
• Incorrect or missing dependencies: Verify that you’ve passed the correct dependencies to the useMutation hook, and that they are up-to-date.
• Inconsistent caching: Apollo Client’s cache can sometimes interfere with the rerendering process. Try disabling caching or using a different cache policy.
• Competing updates: If multiple updates are being triggered simultaneously, it might prevent the component from rerendering. Use useCallback or useMemo to memoize your mutation function and dependencies.

The Investigation: Understanding the useMutation Hook

To grasp why useMutation doesn’t fire a rerender, we need to understand how it works under the hood.

import { useMutation, gql } from '@apollo/client';

const MUTATION = gql`
  mutation CreateItem($name: String!) {
    createItem(name: $name) {
      id
      name
    }
  }
`;

function CreateItem() {
  const [createItem, { data, error, loading }] = useMutation(MUTATION);

  if (loading) return 
Loading...
;
  if (error) return 
Error: {error.message}
;

  return (
    

       createItem({ variables: { name: 'New Item' } })}>
        Create Item
      
      {data && 
Item created: {data.createItem.name}
}
    
  );
}

In the above example, the useMutation hook returns an array with three elements:

1. createItem: The mutation function that triggers the update.
2. { data, error, loading }: An object containing the mutation’s result, error, and loading state.

When the mutation is executed, Apollo Client updates its cache and notifies React to rerender the component. However, if the rerender doesn’t occur, it might be due to one of the suspects mentioned earlier.

The Solutions: Fixing the Rerender Issue

Now that we’ve identified the potential causes and understand how useMutation works, let’s dive into the solutions:

Solution 1: Memoize the Mutation Function

Wrap your mutation function with useCallback to memoize it and prevent unnecessary re-renders:

import { useCallback } from 'react';
import { useMutation, gql } from '@apollo/client';

const MUTATION = gql`
  mutation CreateItem($name: String!) {
    createItem(name: $name) {
      id
      name
    }
  }
`;

function CreateItem() {
  const [createItem, { data, error, loading }] = useMutation(MUTATION);

  const memoizedCreateItem = useCallback(() => {
    createItem({ variables: { name: 'New Item' } });
  }, [createItem]);

  return (
    

      Create Item
      {data && 
Item created: {data.createItem.name}
}
    
  );
}

Solution 2: Update Dependencies Correctly

Ensure that you’re passing the correct dependencies to the useMutation hook:

import { useMutation, gql } from '@apollo/client';

const MUTATION = gql`
  mutation CreateItem($name: String!) {
    createItem(name: $name) {
      id
      name
    }
  }
`;

function CreateItem() {
  const [createItem, { data, error, loading }] = useMutation(MUTATION, {
    variables: { name: 'New Item' },
    update: (cache, { data }) => {
      cache.modify({
        fields: {
          items: (existingItems = []) => [...existingItems, data.createItem],
        },
      });
    },
  });

  return (
    

      Create Item
      {data && 
Item created: {data.createItem.name}
}
    
  );
}

Solution 3: Disable Caching or Use a Different Cache Policy

Apollo Client’s cache can sometimes interfere with the rerendering process. Try disabling caching or using a different cache policy:

import { ApolloClient, InMemoryCache } from '@apollo/client';

const client = new ApolloClient({
  uri: 'https://your-graphql-api.com/graphql',
  cache: new InMemoryCache({
    typePolicies: {
      Query: {
        fields: {
          items: {
            merge: (existing, incoming) => [...existing, ...incoming],
          },
        },
      },
    },
  }),
});

Solution 4: Use useQuery Instead of useMutation

In some cases, you might be able to use useQuery instead of useMutation. If you’re performing a query that updates the cache, consider using useQuery with the refetch option:

import { useQuery, gql } from '@apollo/client';

const QUERY = gql`
  query GetItems {
    items {
      id
      name
    }
  }
`;

function GetItems() {
  const { data, error, refetch } = useQuery(QUERY, {
    refetch: true,
  });

  if (error) return 
Error: {error.message}
;

  return (
    

      Refetch Items
      {data && (
        

          {data.items.map((item) => (
            
{item.name}
          ))}
        
      )}
    
  );
}

Conclusion: Solving the useMutation Rerender Mystery

By now, you should have a solid understanding of why useMutation might not be firing a rerender in your React application, and how to fix it using the solutions outlined above. Remember to:

• Check for common culprits such as incorrect dependencies or caching issues.
• Memoize your mutation function to prevent unnecessary re-renders.
• Update dependencies correctly to ensure the mutation is triggered correctly.
• Disable caching or use a different cache policy if necessary.
• Consider using useQuery instead of useMutation if possible.

With these solutions in your toolkit, you’ll be well-equipped to tackle the mysterious case of useMutation not firing a rerender in React. Happy debugging!

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