GraphQL Middleware
Subject to change
Resolver-based middleware is functional and fully implemented but its API might be subject to change.
It is currently only supported as extensions to Graphiti (opens in a new tab), and only available in v1.2.0-beta.1 or higher.
Middlewares are useful reusable code that can be easily attached to resolvers. It allows you to perform operations on incoming operations before they get to the field resolver and on outgoing responses before they are sent back.
Creating a middleware
GraphQL middleware is a function that takes 2 arguments:
- Resolver parameters - All information given to the resolver (root, args, context)
- Next function - Function to control the execution of the next middleware and the resolver to which it is attached
public func MinZeroResult(
params: ResolverParameters<Resolver, Context, NoArguments>,
next: @escaping () -> Int
) async throws -> Int {
try await min(next(), 0)
}public func Trace<Root, Args, Returned>() -> GraphQLMiddleware<Root, Context, Args, Returned> {
return { params, next in
let before = Date()
let res = try await next()
let after = Date()
params.ctx.logger.info("Operation takes \(after.timeIntervalSince(before))s")
return res
}
}Intercepting the resolver
Middleware also has the ability to intercept the result of a resolver's execution.
As an example would be an auth guard:
public func Auth<Root, Args, Returned>() -> GraphQLMiddleware<Root, Context, Args, Returned> {
return { params, next in
guard case .some = params.ctx.user else {
throw GraphQLError(message: "Not authenticated")
}
return try await next()
}
}Another one would be a cache interceptor:
public func Cached<Root, Returned: RESPValueConvertible>(
key: String
) -> GraphQLMiddleware<Root, Context, NoArguments, Returned> {
return { params, next in
guard let cache = try? await redis.get(key, as: Returned.self).get() else {
return cache
}
return try await next()
}
}Attaching Middleware
Attaching middlewares can be done through the use parameter from Field. The order of the middleware is also important.
Query {
// Trace -> Cached -> Resolver
Field("books", at: Resolver.books, use: [Trace(), Cached(key: "query:books")])
}
Mutation {
// Auth -> Trace -> Resolver
Field("createBook", at: Resolver.createBook, use: [Auth(), Trace()])
}