# Juniper — GraphQL Server Library for Rust

> Juniper is a code-first GraphQL server library for Rust that uses macros to derive GraphQL schemas directly from Rust types, providing type-safe query execution with zero runtime overhead.

## Install

Save as a script file and run:

# Juniper — GraphQL Server Library for Rust

## Quick Use
```rust
// Cargo.toml
// [dependencies]
// juniper = "0.16"
// juniper_warp = "0.8"

use juniper::{graphql_object, EmptyMutation, EmptySubscription, RootNode};

struct Query;

#[graphql_object]
impl Query {
    fn hello() -> &str { "Hello, world!" }
}

type Schema = RootNode<'static, Query, EmptyMutation, EmptySubscription>;
```

## Introduction
Juniper brings GraphQL to the Rust ecosystem with a code-first approach where your Rust structs and enums become the GraphQL schema. By leveraging Rust's type system and procedural macros, Juniper catches schema errors at compile time and produces a GraphQL server with the same memory safety and performance guarantees that Rust provides.

## What Juniper Does
- Derives GraphQL types from Rust structs, enums, and trait implementations using procedural macros
- Executes GraphQL queries, mutations, and subscriptions with compile-time type safety
- Integrates with web frameworks including Actix-web, Warp, Hyper, and Rocket
- Supports the full GraphQL specification including interfaces, unions, input objects, and custom scalars
- Provides built-in support for async resolvers using Rust's async/await

## Architecture Overview
Juniper uses a derive-macro system to generate GraphQL type metadata from annotated Rust types at compile time. When a query arrives, the executor parses the GraphQL document, validates it against the generated schema, and resolves fields by calling the corresponding Rust methods. The execution engine handles field-level parallelism for async resolvers. Integration crates (juniper_warp, juniper_actix, etc.) bridge the executor to HTTP endpoints.

## Self-Hosting & Configuration
- Add `juniper` to Cargo.toml along with an integration crate for your web framework
- Define a Context type to hold database connections, auth state, and other per-request data
- Annotate structs with `#[derive(GraphQLObject)]` for simple output types or use `#[graphql_object]` for resolver logic
- Mount the GraphQL endpoint and optionally enable GraphiQL or GraphQL Playground for development
- Configure subscription support with `juniper_subscriptions` for WebSocket-based real-time data

## Key Features
- Compile-time schema validation ensures type mismatches and missing fields are caught before deployment
- Async resolver support allows non-blocking database queries and external API calls
- N+1 query prevention through integration with DataLoader patterns
- Custom scalar types for domain-specific values like dates, UUIDs, and URLs
- Schema introspection endpoint compatible with GraphQL IDEs and code generators

## Comparison with Similar Tools
- **async-graphql** — Rust alternative with attribute macros and built-in subscription support; Juniper has a longer track record and broader framework integration
- **Apollo Server** — Node.js GraphQL server with a rich plugin ecosystem; Juniper offers Rust's performance and memory safety
- **Strawberry** — Python GraphQL with dataclass-based schema; Juniper provides similar ergonomics in Rust with compile-time checks
- **Hot Chocolate** — .NET GraphQL server; Juniper trades the .NET runtime for Rust's zero-cost abstractions
- **Hasura** — Auto-generates GraphQL from database schema; Juniper gives full control over resolver logic and business rules

## FAQ
**Q: Does Juniper support GraphQL subscriptions?**
A: Yes. The `juniper_subscriptions` crate adds subscription support using async streams, compatible with the GraphQL over WebSocket protocol.

**Q: Which web framework should I use with Juniper?**
A: Juniper provides integration crates for Actix-web, Warp, Hyper, and Rocket. Choose based on your project's existing framework or performance requirements.

**Q: Can I use Juniper with an existing database ORM?**
A: Yes. Juniper resolvers are regular Rust functions that can call Diesel, SeaORM, sqlx, or any other database library through the context object.

**Q: How do I handle authentication in Juniper?**
A: Extract auth tokens in your web framework's middleware, validate them, and pass the authenticated user into Juniper's Context. Resolvers then access the context to enforce authorization.

## Sources
- https://github.com/graphql-rust/juniper
- https://graphql-rust.github.io/juniper/

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Author: Script Depot