Question 1

How do I add authentication to a Mercurius GraphQL server?

Accepted Answer

Mercurius doesn't have built-in authentication; you need to use Fastify hooks or plugins. For example, add a preHandler hook in Fastify to validate JWT tokens before GraphQL execution, as referenced in the context and lifecycle docs.

Question 2

Mercurius vs Apollo Server for Fastify: which is better?

Accepted Answer

Mercurius is optimized for Fastify with better integration and performance features like JIT compilation, while Apollo Server has a larger ecosystem and tooling. Choose Mercurius if you're committed to Fastify and prioritize speed; Apollo if you need extensive plugins or aren't tied to Fastify.

Question 3

Can I use Mercurius with TypeScript?

Accepted Answer

Yes, Mercurius supports TypeScript with a dedicated documentation page. You can define types for schemas and resolvers, though it may require manual type definitions for advanced features like context.

Question 4

How to set up GraphQL subscriptions with Mercurius?

Accepted Answer

Enable subscriptions by configuring the WebSocket transport in Mercurius options and defining subscription resolvers. The subscriptions documentation provides examples for real-time updates over GraphQL.

Question 5

Does Mercurius support persisted queries for security?

Accepted Answer

Yes, Mercurius allows customizable persisted queries where queries are stored server-side and referenced by ID, improving security by limiting exposed query strings, as mentioned in the features.

Question 6

What's the performance impact of using Mercurius with JIT compilation?

Accepted Answer

JIT compilation via graphql-jit can significantly speed up query execution by compiling GraphQL operations to native code, but it may increase initial load time for complex schemas and requires monitoring for memory usage in production.

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