Contextual Data

All GraphQL servers have a concept of a "context". A GraphQL context contains metadata that is useful to the GraphQL server, but shouldn't necessarily be part of the GraphQL schema. A prime example of something that is appropriate for the GraphQL context would be trace headers for an OpenTracing system such as Haystack. The GraphQL query does not need the information to perform its function, but the server needs the information to ensure observability.

The contents of the GraphQL context vary across applications and it is up to the GraphQL server developers to decide what it should contain. graphql-kotlin-server provides a simple mechanism to build a context per operation with the GraphQLContextFactory. If a custom factory is defined, it will then be used to populate GraphQL context based on the incoming request and make it available during execution.

GraphQL Context Map

In graphql-java v17 a new context map was added to the DataFetchingEnvironment. This is now the way of saving info for execution, and you can access this map through the DataFetchingEnvironment.

class ContextualQuery : Query {
    fun contextualQuery(
        dataFetchingEnvironment: DataFetchingEnvironment,
        value: Int
    ): String =
        "The custom value was ${dataFetchingEnvironment.graphQLContext.get("foo")} and the value was $value"
}