Are graphql codegen types correct

Are GraphQL Codegen Types Correct?

When working with GraphQL and TypeScript, one common challenge is ensuring that the generated types from GraphQL Codegen are correct. In this article, we will explore this issue and discuss possible solutions.

Understanding the Problem

GraphQL Codegen is a powerful tool that automatically generates TypeScript types based on your GraphQL schema and queries. However, there are situations where the generated types may not be accurate or up-to-date, leading to potential runtime errors.

There are a few reasons why the generated types might not be correct:

Schema Changes: If the GraphQL schema evolves over time, the generated types may not reflect the latest changes.
Custom Scalars: If your schema includes custom scalar types, the generated types may not handle them correctly.
Union and Interface Types: The generated types may not accurately represent union and interface types, leading to potential type mismatches.

Solutions

Let’s explore some solutions to ensure that the generated types from GraphQL Codegen are correct:

1. Regularly Update GraphQL Schema

To address the issue of schema changes, it is crucial to regularly update your GraphQL schema in the codebase. This can be done by fetching the latest schema from the server or by manually updating the schema file.

Once the schema is updated, you can run GraphQL Codegen to generate the latest types based on the updated schema. This ensures that the generated types accurately reflect the current state of the schema.

Code Snippet:

npx graphql-codegen --config codegen.yml

2. Customize Scalars

If your schema includes custom scalar types, you may need to customize the generated types to handle them correctly. GraphQL Codegen allows you to define custom scalars in the configuration file and specify how they should be represented in the generated types.

By providing custom scalar mappings, you can ensure that the generated types correctly handle the custom scalars in your schema.

Code Snippet:

config:
  scalars:
    DateTime: Date

3. Use Fragments for Union and Interface Types

When working with union and interface types, it is common to encounter type mismatches in the generated types. To address this issue, you can use fragments to explicitly specify the fields and types for each possible variant of the union or interface.

By using fragments, you can ensure that the generated types accurately represent the union and interface types, avoiding potential type errors.

Code Snippet:

query GetProduct {
  product {
    ... on Book {
      title
      author
    }
    ... on Movie {
      title
      director
    }
  }
}

Conclusion

Ensuring that the generated types from GraphQL Codegen are correct is essential for building robust and error-free TypeScript applications. By regularly updating the schema, customizing scalars, and using fragments for union and interface types, you can overcome the challenges and ensure accurate types in your codebase.

Remember to run GraphQL Codegen whenever there are schema changes to keep your types up-to-date and prevent potential runtime errors.

Happy coding!

Are graphql codegen types correct