FSharp.Data.GraphQL is a client and server implementation of Facebook's GraphQL query language.

It's a standard created for building web service APIs and a runtime for defining those APIs in statically typed, well formed way. The core idea is to define web service in context of its capabilities in oposition to routees known from existing RESTful APIs. Capabilities are defined in form of GraphQL schema and describe all operations and data allowed to be requested by the client, without fragmenting it into particular routes.

The FSharp.Data.GraphQL library can be installed from NuGet on the server or a client:

PM> Install-Package FSharp.Data.GraphQL.Server
PM> Install-Package FSharp.Data.GraphQL.Client

To use FSharp.Data.GraphQL on the server side, first define some data working as a source:

type Person = { FirstName: string; LastName: string }
let people = [ 
    { FirstName = "Jane"; LastName = "Milton" }
    { FirstName = "Travis"; LastName = "Smith" } ]

Then expose it through the schema - GraphQL language defines it's own type system, that can be integrated with any other programming language:

open FSharp.Data.GraphQL
open FSharp.Data.GraphQL.Types

// GraphQL type definition for Person type
let Person = Define.Object("Person", [
    Define.Field("firstName", String, fun ctx p -> p.FirstName)
    Define.Field("lastName", String, fun ctx p -> p.LastName)  
])

// Each schema must define so-called root query
let QueryRoot = Define.Object("Query", [
    Define.Field("people", ListOf Person, fun ctx () -> people)
])

// Then initialize everything as part of schema
let schema = Schema(QueryRoot)

With schema create we are now able to respond to any incoming GraphQL queries:

// Create an Exector for the schema
let executor = Executor(schema)

let query = """
    query Example {
        people {
            firstName
        }
    }
    """
    
async {
    let! response = executor.AsyncExecute(query)
    printf "%A" response
}

For more examples, clone FSharp.Data.GraphQL github repository and see the samples folder. There, your can find:

• A mandatory Star Wars schema introduction using GraphiQL client.
• An example using RelayJS data structures (which this library supports).

The project is hosted on GitHub where you can report issues, fork the project and submit pull requests. If you're adding a new public API, please also consider adding samples that can be turned into a documentation. You might also want to read the library design notes to understand how it works.

The library is available under Public Domain license, which allows modification and redistribution for both commercial and non-commercial purposes. For more information see the License file in the GitHub repository.