GraphQL

The Swift implementation for GraphQL, a query language for APIs created by Facebook.

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Usage

Schema Definition

The GraphQLSchema object can be used to define GraphQL Schemas and Types. These schemas are made up of types, fields, arguments, and resolver functions. Below is an example:

let schema = try GraphQLSchema(
    query: GraphQLObjectType(                   // Defines the special "query" type
        name: "Query",
        fields: [
            "hello": GraphQLField(              // Users may query 'hello'
                type: GraphQLString,            // The result is a string type
                resolve: { _, _, _, _ in
                    "world"                     // The result of querying 'hello' is "world"
                }
            )
        ]
    )
)

For more complex schema examples see the test files.

This repo only contains the core GraphQL implementation and does not focus on the ease of schema creation. For a better experience when creating your GraphQL schema use Graphiti.

Execution

Once a schema has been defined queries may be executed against it using the global graphql function:

let result = try await graphql(
    schema: schema,
    request: "{ hello }",
    eventLoopGroup: eventLoopGroup
)

The result of this query is a GraphQLResult that encodes to the following JSON:

{ "hello": "world" }

Subscription

This package supports GraphQL subscription, but until the integration of AsyncSequence in Swift 5.5 the standard Swift library did not provide an event-stream construct. For historical reasons and backwards compatibility, this library implements subscriptions using an EventStream protocol that nearly every asynchronous stream implementation can conform to.

To create a subscription field in a GraphQL schema, use the subscribe resolver that returns an EventStream. You must also provide a resolver, which defines how to process each event as it occurs and must return the field result type. Here is an example:

let schema = try GraphQLSchema(
    subscribe: GraphQLObjectType(
        name: "Subscribe",
        fields: [
            "hello": GraphQLField(              
                type: GraphQLString,
                resolve: { eventResult, _, _, _, _ in       // Defines how to transform each event when it occurs
                    return eventResult
                },
                subscribe: { _, _, _, _, _ in               // Defines how to construct the event stream
                    let asyncStream = AsyncThrowingStream<String, Error> { continuation in
                        let timer = Timer.scheduledTimer(
                            withTimeInterval: 3,
                            repeats: true,
                        ) {
                            continuation.yield("world")     // Emits "world" every 3 seconds
                        }
                    }
                    return ConcurrentEventStream<String>(asyncStream)
                }
            )
        ]
    )
)

To execute a subscription use the graphqlSubscribe function:

let subscriptionResult = try await graphqlSubscribe(
    schema: schema,
)
// Must downcast from EventStream to concrete type to use in 'for await' loop below
let concurrentStream = subscriptionResult.stream! as! ConcurrentEventStream
for try await result in concurrentStream.stream {
    print(result)
}

The code above will print the following JSON every 3 seconds:

{ "hello": "world" }

The example above assumes that your environment has access to Swift Concurrency. If that is not the case, try using GraphQLRxSwift

Encoding Results

If you encode a GraphQLResult with an ordinary JSONEncoder, there are no guarantees that the field order will match the query, violating the GraphQL spec. To preserve this order, GraphQLResult should be encoded using the GraphQLJSONEncoder provided by this package.

Contributing

If you think you have found a security vulnerability, please follow the Security guidelines.

Those contributing to this package are expected to follow the Swift Code of Conduct, the Swift API Design Guidelines, and the SSWG Technical Best Practices.

This repo uses SwiftFormat, and includes lint checks to enforce these formatting standards. To format your code, install swiftformat and run:

swiftformat .

Most of this repo mirrors the structure of (the canonical GraphQL implementation written in Javascript/Typescript)[https://github.com/graphql/graphql-js]. If there is any feature missing, looking at the original code and “translating” it to Swift works, most of the time. For example:

Swift

/Sources/GraphQL/Language/AST.swift

Javascript/Typescript

/src/language/ast.js

License

This project is released under the MIT license. See LICENSE for details.