How can I parse a custom scalar in Apollo Client?

If you’re working with Apollo Client and need to parse a custom scalar, you’re in the right place. In this blog post, we’ll explore different solutions to this problem.

Solution 1: Using a custom type policy

One way to parse a custom scalar in Apollo Client is by using a custom type policy. This approach allows you to define how the scalar should be serialized and deserialized.

First, you need to define your custom scalar type policy using the typePolicies option when creating your Apollo Client instance:


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

const client = new ApolloClient({
  cache: new InMemoryCache({
    typePolicies: {
      MyCustomScalar: {
        serialize(value) {
          // Serialize the scalar value
          return value.toString();
        },
        parseValue(value) {
          // Parse the scalar value
          return new MyCustomScalar(value);
        },
        parseLiteral(ast) {
          // Parse the scalar value from the AST
          return new MyCustomScalar(ast.value);
        },
      },
    },
  }),
});

In the above code snippet, replace MyCustomScalar with the name of your custom scalar type.

Solution 2: Using a custom link

Another approach to parse a custom scalar in Apollo Client is by using a custom link. This allows you to intercept and modify the data before it reaches the cache.

First, create a custom link that will handle the parsing of the custom scalar:


import { ApolloLink } from '@apollo/client';

const customLink = new ApolloLink((operation, forward) => {
  // Intercept the data and modify it as needed
  operation.setContext(({ headers }) => ({
    headers: {
      ...headers,
      'Custom-Scalar': 'parsed',
    },
  }));

  return forward(operation);
});

Next, add the custom link to your Apollo Client instance:


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

const client = new ApolloClient({
  link: customLink.concat(new HttpLink({ uri: 'http://example.com/graphql' })),
  cache: new InMemoryCache(),
});

Make sure to replace 'http://example.com/graphql' with the actual GraphQL endpoint URL.

Conclusion

In this blog post, we explored two different solutions for parsing a custom scalar in Apollo Client. You can either use a custom type policy or a custom link, depending on your specific requirements.

By following the provided code snippets, you should be able to successfully parse a custom scalar in Apollo Client and handle it according to your needs.

How can I parse a custom scalar in Apollo Client?