Juniper — GraphQL Library for Rust

Juniper is a powerful and performant library for creating GraphQL APIs in the Rust language. It provides developers with convenient macros and types for quickly building schemas, resolvers, and handling queries. Juniper is ideal for projects where speed, type safety, and low memory consumption — Rust's strengths — are critical.

The library supports both synchronous and asynchronous resolvers (via async-trait), integration with popular web frameworks (Actix-web, Rocket, Warp, Axum), as well as advanced features: subscriptions, fragments, directives, and custom scalars.

Key Features of Juniper

Macros for rapid development: #[derive(GraphQLObject)], #[derive(GraphQLInputObject)], #[graphql_interface] automatically generate GraphQL types from Rust structs.
Compile-time type safety: all schema and data type mismatch errors are caught at build time, not at runtime.
Async support: built-in integration with async/await via juniper::graphql_object and async-graphql.
Flexible resolvers: ability to use context, databases, external APIs, and complex business logic.
Subscriptions (WebSockets): implementation of real-time notifications using futures.
Support for GraphQL Playground and GraphiQL: built-in tools for testing queries.

Installation and Setup

Add Juniper to your project via Cargo.toml:

[dependencies]juniper = "0.16"# For async support:juniper = { version = "0.16", features = ["async-trait"] }# For integration with Actix-web:actix-web = "4"juniper-actix = "2"

The basic schema structure consists of three elements: Query, Mutation, and Subscription. Below is an example of a simple API for managing a list of books.

Code Example: Creating a Simple GraphQL API

use juniper::{graphql_object, FieldResult, GraphQLObject, RootNode};

// Data model#[derive(GraphQLObject)]struct Book {    id: String,    title: String,    author: String,    year: i32,}

// Context (e.g., database access)struct Context {    pub books: Vec<Book>,}impl juniper::Context for Context {}

// Resolvers for Querystruct Query;#[graphql_object]#[graphql(context = Context)]impl Query {    fn books(context: &Context) -> &Vec<Book> {        &context.books    }

    fn book_by_id(context: &Context, id: String) -> FieldResult<&Book> {        context.books.iter()            .find(|b| b.id == id)            .ok_or_else(|| juniper::FieldError::new("Book not found", graphql_value!({"code": "NOT_FOUND"})))    }}

// Resolvers for Mutationstruct Mutation;#[graphql_object]#[graphql(context = Context)]impl Mutation {    fn add_book(context: &mut Context, title: String, author: String, year: i32) -> FieldResult<Book> {        let new_book = Book {            id: uuid::Uuid::new_v4().to_string(),            title,            author,            year,        };        context.books.push(new_book);        Ok(new_book)    }}

// Creating the root nodepub type Schema = RootNode<'static, Query, Mutation>;

// Entry point for processing a querypub fn create_schema() -> Schema {    Schema::new(Query, Mutation)}

To run the server on Actix-web, use the ready-made connector: