Intro to elm-graphql

elm-graphql is an Elm package and accompanying command-line code generator that creates type-safe Elm code for your GraphQL endpoint. You don't write any decoders for your API with elm-graphql, instead you simply select which fields you would like, similar to a standard GraphQL query but in Elm. For example, this GraphQL query

query {
  human(id: "1001") {
    name
  }
}

would look like this in elm-graphql (all the generated code is prefixed, in this example with Swapi.)

import Graphqelm.Operation exposing (RootQuery)
import Graphqelm.SelectionSet exposing (SelectionSet, with)
import Swapi.Object
import Swapi.Object.Human as Human
import Swapi.Query as Query


type alias Response =
    { vader : Maybe Human }


query : SelectionSet Response RootQuery
query =
    Query.selection Response
        |> with (Query.human { id = Swapi.Scalar.Id "1001" } human)


type alias Human =
    { name : String }


human : SelectionSet Human Swapi.Object.Human
human =
    Human.selection Human
        |> with Human.name

GraphQL and Elm are a perfect match because GraphQL is used to enforce the types that your API takes as inputs and outputs, much like Elm's type system does within Elm. elm-graphql simply bridges this gap by making your Elm code aware of your GraphQL server's schema. If you are new to GraphQL, graphql.org/learn/ is an excellent way to learn the basics.

After installing the command line tool and Elm package, running elm-graphql just looks like

graphqelm https://graphqelm.herokuapp.com --base Swapi --output examples/src