juniper-from-schema

Important notice: This project is still in a very experimental state. It does work but the API might change drastically.

This library exposes a procedural macro that reads a GraphQL schema file, and generates the corresponding Juniper macro calls. This means you can have a real schema file and be guaranteed that it matches your Rust implementation. It also removes most of the boilerplate from using Juniper.

Example

Schema:

schema {
  query: Query
  mutation: Mutation
}

type Query {
  // this makes the return value `FieldResult<String>`
  // rather than the default `FieldResult<&String>`
  "#[ownership(owned)]"
  helloWorld(name: String!): String!
}

type Mutation {
  noop: Boolean!
}

Rust implementation of schema:

#[macro_use]
extern crate juniper;

use juniper::*;
use juniper_from_schema::graphql_schema_from_file;

// This is the important line
graphql_schema_from_file!("tests/schemas/doc_schema.graphql");

pub struct Context;
impl juniper::Context for Context {}

pub struct Query;

impl QueryFields for Query {
    fn field_hello_world(
        &self,
        executor: &Executor<'_, Context>,
        name: String,
    ) -> FieldResult<String> {
        Ok(format!("Hello, {}!", name))
    }
}

pub struct Mutation;

impl MutationFields for Mutation {
    fn field_noop(&self, executor: &Executor<'_, Context>) -> FieldResult<&bool> {
        Ok(&true)
    }
}

fn main() {
    let ctx = Context;

    let query = "query { helloWorld(name: \"Ferris\") }";

    let (result, errors) = juniper::execute(
        query,
        None,
        &Schema::new(Query, Mutation),
        &Variables::new(),
        &ctx,
    )
    .unwrap();

    assert_eq!(errors.len(), 0);
    assert_eq!(
        result
            .as_object_value()
            .unwrap()
            .get_field_value("helloWorld")
            .unwrap()
            .as_scalar_value::<String>()
            .unwrap(),
        "Hello, Ferris!",
    );
}

This expands into:

#[macro_use]
extern crate juniper;

use juniper::*;

pub struct Context;
impl juniper::Context for Context {}

pub struct Query;

graphql_object!(Query: Context |&self| {
    field hello_world(&executor, name: String) -> FieldResult<String> {
        <Self as QueryFields>::field_hello_world(&self, &executor, name)
    }
});

trait QueryFields {
    fn field_hello_world(
        &self,
        executor: &Executor<'_, Context>,
        name: String,
    ) -> FieldResult<String>;
}

impl QueryFields for Query {
    fn field_hello_world(
        &self,
        executor: &Executor<'_, Context>,
        name: String,
    ) -> FieldResult<String> {
        Ok(format!("Hello, {}!", name))
    }
}

pub struct Mutation;

graphql_object!(Mutation: Context |&self| {
    field noop(&executor) -> FieldResult<&bool> {
        <Self as MutationFields>::field_noop(&self, &executor)
    }
});

trait MutationFields {
    fn field_noop(&self, executor: &Executor<'_, Context>) -> FieldResult<&bool>;
}

impl MutationFields for Mutation {
    fn field_noop(&self, executor: &Executor<'_, Context>) -> FieldResult<&bool> {
        Ok(&true)
    }
}

type Schema = juniper::RootNode<'static, Query, Mutation>;

fn main() {
    let ctx = Context;

    let query = "query { helloWorld(name: \"Ferris\") }";

    let (result, errors) = juniper::execute(
        query,
        None,
        &Schema::new(Query, Mutation),
        &Variables::new(),
        &ctx,
    )
    .unwrap();

    assert_eq!(errors.len(), 0);
    assert_eq!(
        result
            .as_object_value()
            .unwrap()
            .get_field_value("helloWorld")
            .unwrap()
            .as_scalar_value::<String>()
            .unwrap(),
        "Hello, Ferris!",
    );
}

Customizing ownership

By default all fields return borrowed values. Specifically the type is juniper::FieldResult<&'a T> where 'a is the lifetime of self. This works well for returning data owned by self and avoids needless .clone() calls you would need if fields returned owned values.

However if you need to return owned values (such as values queried from a database) you have to annotate the field in the schema with #[ownership(owned)].

All field arguments will be owned.

GraphQL features

The goal of this library is to support as much of GraphQL as Juniper does.

Here is the complete list of features:

Supported:

Object types including converting lists on non-nulls to Rust types
Custom scalar types including the ID type
Interfaces
Unions
Input objects
Enumeration types

Not supported yet:

Default values for arguments
Subscriptions (currently not supported by Juniper so we're unsure when or if this will happen)

The `ID` type

The ID GraphQL type will be generated as a newtype wrapper around a String using juniper::graphql_scalar!. The Rust type will be called Id.

Example:

pub struct Id(pub String);

impl Id {
    // A generated convenience initializer
    pub fn new<T: Into<String>>(id: T) -> Self {
        Id(id.into())
    }
}

Custom scalar types

Similarly to ID, custom scalar types get converted into newtype wrappers around Strings. For example:

scalar Cursor

Would result in

pub struct Cursor(pub String);

Date and DateTime are the two exceptions to this. Date gets converted into chrono::naive::NaiveDate and DateTime into chrono::DateTime<chrono::offset::Utc>.

Interfaces

Juniper has several ways of representing GraphQL interfaces in Rust. They are listed here along with their advantages and disadvantages.

For the generated code we use the enum pattern because we found it to be the most flexible.

Example:

#
graphql_schema! {
    schema {
        query: Query
    }

    type Query {
        "#[ownership(owned)]"
        search(query: String!): [SearchResult!]!
    }

    interface SearchResult {
        id: ID!
        text: String!
    }

    type Article implements SearchResult {
        id: ID!
        text: String!
    }

    type Tweet implements SearchResult {
        id: ID!
        text: String!
    }
}

pub struct Query;

impl QueryFields for Query {
    fn field_search(
        &self,
        executor: &Executor<'_, Context>,
        trail: &QueryTrail<'_, SearchResult, Walked>,
        query: String,
    ) -> FieldResult<Vec<SearchResult>> {
        let article: Article = Article { id: Id::new("1"), text: "Business".to_string() };
        let tweet: Tweet = Tweet { id: Id::new("2"), text: "1 weird tip".to_string() };

        let posts = vec![
            SearchResult::from(article),
            SearchResult::from(tweet),
        ];

        Ok(posts)
    }
}

The enum that gets generated has variants for each type that implements the interface and also implements From<T> for each type.

Union types

Union types are basically just interfaces so they work in very much the same way.

Example:

#
graphql_schema! {
    schema {
        query: Query
    }

    type Query {
        "#[ownership(owned)]"
        search(query: String!): [SearchResult!]!
    }

    union SearchResult = Article | Tweet

    type Article {
        id: ID!
        text: String!
    }

    type Tweet {
        id: ID!
        text: String!
    }
}

pub struct Query;

impl QueryFields for Query {
    fn field_search(
        &self,
        executor: &Executor<'_, Context>,
        trail: &QueryTrail<'_, SearchResult, Walked>,
        query: String,
    ) -> FieldResult<Vec<SearchResult>> {
        let article: Article = Article { id: Id::new("1"), text: "Business".to_string() };
        let tweet: Tweet = Tweet { id: Id::new("2"), text: "1 weird tip".to_string() };

        let posts = vec![
            SearchResult::from(article),
            SearchResult::from(tweet),
        ];

        Ok(posts)
    }
}

Input objects

Input objects will be converted into Rust structs with public fields.

Example:

graphql_schema! {
    schema {
        query: Query
        mutation: Mutation
    }

    type Mutation {
        "#[ownership(owned)]"
        createPost(input: CreatePost!): Post
    }

    input CreatePost {
        title: String!
    }

    type Post {
        id: ID!
        title: String!
    }

    type Query { noop: Boolean! }
}

pub struct Mutation;

impl MutationFields for Mutation {
    fn field_create_post(
        &self,
        executor: &Executor<'_, Context>,
        trail: &QueryTrail<'_, Post, Walked>,
        input: CreatePost,
    ) -> FieldResult<Option<Post>> {
        let title: String = input.title;

        unimplemented!()
    }
}

From that example CreatePost will be defined as

pub struct CreatePost {
    pub title: String,
}

Enumeration types

GraphQL enumeration types will be converted into normal Rust enums. The name of each variant will be camel cased.

Example:

#
graphql_schema! {
    schema {
        query: Query
    }

    enum Status {
        PUBLISHED
        UNPUBLISHED
    }

    type Query {
        "#[ownership(owned)]"
        allPosts(status: STATUS!): [Post!]!
    }

    type Post {
        id: ID!
    }
}

pub struct Query;

impl QueryFields for Query {
    fn field_all_posts(
        &self,
        executor: &Executor<'_, Context>,
        trail: &QueryTrail<'_, Post, Walked>,
        status: Status,
    ) -> FieldResult<Vec<Post>> {
        match status {
            Status::Published => unimplemented!("find published posts"),
            Status::Unpublished => unimplemented!("find unpublished posts"),
        }
    }
}

GraphQL to Rust types

This is how the standard GraphQL types will be mapped to Rust:

Int -> i32
Float -> f64
String -> String
Boolean -> bool
ID -> pub struct Id(pub String)

Query trails

If you're not careful about preloading associations for deeply nested queries you risk getting lots of N+1 query bugs. Juniper provides a look ahead api which lets you inspect things coming up further down a query. However the API is string based, so you risk making typos and checking for fields that don't exist.

QueryTrail is a thin wrapper around Juniper look aheads with generated methods for each field on all your types. This means the compiler will reject your code if you're checking for invalid fields.

Fields that return objects types (non scalar values) will also get a QueryTrail argument besides the executor.

Example

#
graphql_schema! {
    schema {
        query: Query
    }

    type Query {
        "#[ownership(owned)]"
        allPosts: [Post!]!
    }

    type Post {
        id: Int!
        author: User!
    }

    type User {
        id: Int!
    }
}

pub struct Query;

impl QueryFields for Query {
    fn field_all_posts(
        &self,
        executor: &Executor<'_, Context>,
        trail: &QueryTrail<'_, Post, Walked>,
    ) -> FieldResult<Vec<Post>> {
        // Check if the query includes the author
        if let Some(_) = trail.author().walk() {
            // Somehow preload the users to avoid N+1 query bugs
            // Exactly how to do this depends on your setup
        }

        // Normally this would come from the database
        let post = Post {
            id: 1,
            author: User { id: 1 },
        };

        Ok(vec![post])
    }
}

pub struct Post {
    id: i32,
    author: User,
}

impl PostFields for Post {
    fn field_id(&self, executor: &Executor<'_, Context>) -> FieldResult<&i32> {
        Ok(&self.id)
    }

    fn field_author(
        &self,
        executor: &Executor<'_, Context>,
        trail: &QueryTrail<'_, User, Walked>,
    ) -> FieldResult<&User> {
        Ok(&self.author)
    }
}

pub struct User {
    id: i32,
}

impl UserFields for User {
    fn field_id(
        &self,
        executor: &Executor<'_, Context>,
    ) -> FieldResult<&i32> {
        Ok(&self.id)
    }
}

Types

A query trial has two generic parameters: QueryTrail<'_, T, K>. T is the type the current field returns and K is either Walked or NotWalked.

`T`

The T allows us to implement different methods for different types. For example in the example above we implement id and author for QueryTrail<'_, Post, K> but only id for QueryTrail<'_, User, K>.

`K`

The Walked and NotWalked types are used to check if a given trail has been checked to actually be part of a query. Calling any method on a QueryTrail<'_, T, K> will return QueryTrail<'_, T, NotWalked>, and to check if the trail is actually part of the query you have to call .walk() which returns Option<QueryTrail<'_, T, Walked>>. If that is a Some(_) you'll know the trail is part of the query and you can do whatever preloading is necessary.

Example:

if let Some(walked_trail) = trail.some_field().some_other_field().third_field().walk() {
    // preload stuff
}

You can always run cargo doc and inspect all the methods on QueryTrail and in which contexts you can call them.

License: MIT

juniper-from-schema 0.1.0

juniper-from-schema

Example

Customizing ownership

GraphQL features

The ID type

Custom scalar types

Interfaces

Union types

Input objects

Enumeration types

GraphQL to Rust types

Query trails

Example

Types

T

K

The `ID` type

`T`

`K`