Subscription

GraphQL Subscriptions allow a client to subscribe to server updates.

For example, in our schema, if you want to notify a client that a movie has been added; you can add a Subscription like this:

type Query {
    movies: [Movie!]!
}

type Mutation {
    addMovie(title: String!, directorName: String!): Movie!
}

type Subscription {
    onMovieAdded: Movie!
}

type Movie {
    title: String!
    director: Director!
}

type Director {
    name: String!
    movies: [Movie!]
}

Now, you must register a resolver which will returner either a kotlinx.coroutines.flow.Flow either a org.reactivestreams.Publisher.

import kotlinx.coroutines.flow.*

val onMovieAdded = MutableSharedFlow<Movie>()

fun main() = arianeServer {
    resolvers {
        Subscription {
            resolve("onMovieAdded", onMovieAdded)
        }
    }
}.launch()

You can now emit new events like this:

import kotlinx.coroutines.flow.*

val onMovieAdded = MutableSharedFlow<Movie>()

fun main() = arianeServer {
    resolvers {
        Mutation { 
            resolve("addMovie") {
                val movie = Movie(arguments["title"], Director(arguments["director"]))
                movies.add(movie)
                
                onBookAddedPublished.emit(movie)
                
                movie
            }
        }
    }
}.launch()

Filters

If you need to apply filters on the subscriptions, you can apply a filter directly on the resolver.

Example:

type Subscription {
    onMovieAdded(director: String!): Movie!
}

import kotlinx.coroutines.flow.*

val onMovieAdded = MutableSharedFlow<Movie>()

fun main() = arianeServer {
    resolvers {
        Subscription {
            resolve("onMovieAdded", onMovieAdded) {
                movie.director.name == argument["director"]
            }
        }
    }
}.launch()

Filters​

Filters