Enums

GraphQL enum types, like scalar types, also represent leaf values in a GraphQL type system. However enum types describe the set of possible values.

Enums are not references for a numeric value, but are unique values in their own right. They may serialize as a string: the name of the represented value.

With Juniper a GraphQL enum may be defined by using the #[derive(GraphQLEnum)] attribute on a Rust enum as long as its variants do not have any fields:

extern crate juniper;
use juniper::GraphQLEnum;

#[derive(GraphQLEnum)]
enum Episode {
    NewHope,
    Empire,
    Jedi,
}

fn main() {}

Renaming

By default, enum variants are converted from Rust’s standard PascalCase naming convention into GraphQL’s SCREAMING_SNAKE_CASE convention:

extern crate juniper;
use juniper::GraphQLEnum;

#[derive(GraphQLEnum)]
enum Episode {
    NewHope, // exposed as `NEW_HOPE` in GraphQL schema
    Empire,  // exposed as `EMPIRE` in GraphQL schema
    Jedi,    // exposed as `JEDI` in GraphQL schema
}

fn main() {}

We can override the name by using the #[graphql(name = "...")] attribute:

extern crate juniper;
use juniper::GraphQLEnum;

#[derive(GraphQLEnum)]
#[graphql(name = "WrongEpisode")] // now exposed as `WrongEpisode` in GraphQL schema
enum Episode {
    #[graphql(name = "LAST_HOPE")]
    NewHope, // exposed as `LAST_HOPE` in GraphQL schema
    Empire,
    Jedi,
}

fn main() {}

Or provide a different renaming policy for all the enum variants:

extern crate juniper;
use juniper::GraphQLEnum;

#[derive(GraphQLEnum)]
#[graphql(rename_all = "none")] // disables any renaming
enum Episode {
    NewHope, // exposed as `NewHope` in GraphQL schema
    Empire,  // exposed as `Empire` in GraphQL schema
    Jedi,    // exposed as `Jedi` in GraphQL schema
}

fn main() {}

TIP: Supported policies are: SCREAMING_SNAKE_CASE, snake_case, camelCase and none (disables any renaming).

Documentation and deprecation

Just like when defining GraphQL objects, the GraphQL enum type and its values could be documented and deprecated via #[graphql(description = "...")] and #[graphql(deprecated = "...")]/#[deprecated] attributes:

extern crate juniper;
use juniper::GraphQLEnum;

/// This doc comment is visible only in Rust API docs.
#[derive(GraphQLEnum)]
#[graphql(description = "An episode of Star Wars")]
enum StarWarsEpisode {
    /// This doc comment is visible only in Rust API docs.
    #[graphql(description = "This description is visible only in GraphQL schema.")]
    NewHope,

    /// This doc comment is visible only in Rust API docs.
    #[graphql(desc = "Arguably the best one in the trilogy.")]
    //        ^^^^ shortcut for a `description` argument
    Empire,

    /// This doc comment is visible in both Rust API docs and GraphQL schema 
    /// descriptions.
    Jedi,
    
    #[deprecated(note = "Only visible in Rust.")]
    #[graphql(deprecated = "We don't really talk about this one.")]
    //        ^^^^^^^^^^ takes precedence over Rust's `#[deprecated]` attribute
    ThePhantomMenace, // has no description in GraphQL schema
}

fn main() {}

NOTE: Only GraphQL object/interface/input object fields, arguments and GraphQL enum values can be deprecated.

Ignoring

By default, all enum variants are included in the generated GraphQL enum type as values. To prevent including a specific variant, annotate it with the #[graphql(ignore)] attribute:

#![expect(dead_code, reason = "example")]
extern crate juniper;
use juniper::GraphQLEnum;

#[derive(GraphQLEnum)]
enum Episode<T> {
    NewHope,
    Empire,
    Jedi,
    #[graphql(ignore)]
    Legends(T),   // cannot be queried from GraphQL
    #[graphql(skip)]
    //        ^^^^ alternative naming, up to your preference
    CloneWars(T), // cannot be queried from GraphQL
}

fn main() {}

TIP: See more available features in the API docs of the #[derive(GraphQLEnum)] attribute.