Designing Robust GraphQL Mutations: Best Practices to Follow
When building a GraphQL API, it’s easy to fall into common traps that can lead to brittle and inflexible mutations. Fortunately, by following a few simple principles, you can ensure your mutations are robust and future-proof.
Unique Output Types for Each Mutation
One of the most critical mistakes is to have mutations return the resource itself. This approach may seem intuitive, but it limits your ability to add metadata or other resources to the response as your needs change. Instead, use a unique output type with a suffix like “Payload” for each mutation. For example, a CreateUser mutation would have a CreateUserPayload output type.
The Benefits of Unique Output Types
Let’s consider an example. Imagine building a simple blog API with a CreatePost mutation. Initially, you might design the mutation to return a Post object directly. However, what if you later want to add the current viewer object to refresh the list of posts on the viewer’s home screen? With a unique output type, you can easily add new fields to the response without breaking existing code.
Single, Unique Input Type for Each Mutation
While not as crucial as unique output types, it’s also a best practice to have a single input parameter called input for each mutation. This approach, known as the Parameter Object Pattern, simplifies your code and makes it easier to manage large parameter lists. For example, you can rewrite the CreatePost mutation to use a CreatePostInput type, making it easy to add new fields without breaking client code.
Idempotent Mutations with ClientMutationId
One of the most powerful features of the Relay mutation spec is the clientMutationId parameter. This allows your mutations to be made idempotent, ensuring that duplicate requests don’t result in unintended consequences. By using clientMutationId, you can cache responses on the server and return the cached response if a duplicate request is received.
Verb-Based Mutation Names
The Relay spec recommends naming mutations using verbs, which makes sense since mutations take action in your API. Use active words like createPost instead of nouns like postCreation. This approach helps to clearly indicate that some change will occur when calling the mutation.
Standardized Implementation
By following the Relay spec for mutations, you can ensure a standardized implementation that’s easy to maintain and extend. Most common GraphQL libraries, such as Graphene for Python or graphql-js for Node/JavaScript, have built-in support for Relay, making it easy to implement these patterns.
Future-Proof Your API
By following these best practices, you can design robust and future-proof GraphQL mutations that will serve your API well as it grows and evolves. With a standardized implementation and idempotent mutations, you’ll be able to build a scalable and maintainable API that meets the needs of your users.