Feature Flagged Queries

Often in GraphQL there's only one server for a given schema. But sometimes there might be many servers that serve a different schema, and those servers might be serving different versions of that same schema. A classic example of this is the introspection query: servers support a different set of fields depending on which version of the specification they support and/or which RFCs they have implemented on top of that specification.

To support these cases, cynic allows you to associate fields in a QueryFragment with a feature:

#![allow(unused)]
fn main() {
#[derive(cynic::QueryFragment, Debug)]
struct AuthorQuery {
    __typename: String,
    #[cynic(feature = "shiny")]
    shiny_new_field: Option<String>
}

}

This Author struct will only query for shiny_new_field if the shiny feature has been enabled.

To enable features you need to use the lower-level OperationBuilder to build your Operation (rather than the QueryBuilder that is usually recommended):

#![allow(unused)]
fn main() {
let operation = cynic::OperationBuilder::<QueryWithFeatures, ()>::query()
    .with_variables(())
    .with_feature_enabled("shiny")
    .build()?;
}

For examples of this feature in action, take a look in the cynic-introspection crate, which uses it to support multiple versions of the GraphQL specification, and the various RFCs that servers support.