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//! This library contains a procedural macro that reads a GraphQL schema file, and generates the //! corresponding [Juniper](https://crates.io/crates/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 involved in using Juniper. //! //! [macro calls]: https://graphql-rust.github.io/types/objects/complex_fields.html //! //! # Table of contents //! //! - [Example](#example) //! - [Example web app](#example-web-app) //! - [Customizing ownership](#customizing-ownership) //! - [GraphQL features](#graphql-features) //! - [The `ID` type](#the-id-type) //! - [Custom scalar types](#custom-scalar-types) //! - [Special case scalars](#special-case-scalars) //! - [Interfaces](#interfaces) //! - [Union types](#union-types) //! - [Input objects](#input-objects) //! - [Enumeration types](#enumeration-types) //! - [Default argument values](#default-argument-values) //! - [GraphQL to Rust types](#graphql-to-rust-types) //! - [Query trails](#query-trails) //! - [Customizing the error type](#customizing-the-error-type) //! - [Customizing the context type](#customizing-the-context-type) //! - [Inspecting the generated code](#inspecting-the-generated-code) //! //! # Example //! //! Schema: //! //! ```graphql //! schema { //! query: Query //! mutation: Mutation //! } //! //! type Query { //! // The directive makes the return value `FieldResult<String>` //! // rather than the default `FieldResult<&String>` //! helloWorld(name: String!): String! @juniper(ownership: "owned") //! } //! //! type Mutation { //! noop: Boolean! //! } //! ``` //! //! How you could implement that schema: //! //! ``` //! #[macro_use] //! extern crate 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: &juniper::Executor<'_, Context>, //! name: String, //! ) -> juniper::FieldResult<String> { //! Ok(format!("Hello, {}!", name)) //! } //! } //! //! pub struct Mutation; //! //! impl MutationFields for Mutation { //! fn field_noop(&self, executor: &juniper::Executor<'_, Context>) -> juniper::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), //! &juniper::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!", //! ); //! } //! ``` //! //! And with `graphql_schema_from_file!` expanded your code would look something like this: //! //! ``` //! #[macro_use] //! extern crate juniper; //! //! pub struct Context; //! impl juniper::Context for Context {} //! //! pub struct Query; //! //! juniper::graphql_object!(Query: Context |&self| { //! field hello_world(&executor, name: String) -> juniper::FieldResult<String> { //! <Self as QueryFields>::field_hello_world(&self, &executor, name) //! } //! }); //! //! trait QueryFields { //! fn field_hello_world( //! &self, //! executor: &juniper::Executor<'_, Context>, //! name: String, //! ) -> juniper::FieldResult<String>; //! } //! //! impl QueryFields for Query { //! fn field_hello_world( //! &self, //! executor: &juniper::Executor<'_, Context>, //! name: String, //! ) -> juniper::FieldResult<String> { //! Ok(format!("Hello, {}!", name)) //! } //! } //! //! pub struct Mutation; //! //! juniper::graphql_object!(Mutation: Context |&self| { //! field noop(&executor) -> juniper::FieldResult<&bool> { //! <Self as MutationFields>::field_noop(&self, &executor) //! } //! }); //! //! trait MutationFields { //! fn field_noop(&self, executor: &juniper::Executor<'_, Context>) -> juniper::FieldResult<&bool>; //! } //! //! impl MutationFields for Mutation { //! fn field_noop(&self, executor: &juniper::Executor<'_, Context>) -> juniper::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), //! &juniper::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!", //! ); //! } //! ``` //! //! # Example web app //! //! You can find an example of how to use this library together with [Rocket] and [Diesel] to make //! a GraphQL web app at <https://github.com/davidpdrsn/graphql-app-example> or an example of how //! to use this library with [Actix] and [Diesel] at //! <https://github.com/husseinraoouf/graphql-actix-example>. //! //! [Rocket]: https://rocket.rs //! [Diesel]: http://diesel.rs //! [Actix]: https://actix.rs/ //! //! # 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 change the ownership you have to add the directive //! `@juniper(ownership:)` to the field in the schema. //! //! It takes the following arguments: //! //! - `@juniper(ownership: "borrowed")`: The return type will be borrowed from `self` //! (`FieldResult<&T>`). //! - `@juniper(ownership: "owned")`: The return type will be owned (`FieldResult<T>`). //! - `@juniper(ownership: "as_ref")`: Only applicable for `Option` and `Vec` return types. Changes //! the inner type to be borrowed (`FieldResult<Option<&T>>` or `FieldResult<Vec<&T>>`). //! //! 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 and non-nulls to Rust types //! - Custom scalar types including the `ID` type //! - Interfaces //! - Unions //! - Input objects //! - Enumeration types //! //! Not supported yet: //! - Subscriptions (currently not supported by Juniper so we're unsure when or if this will happen) //! - Schema directives (`@deprecated` is supported) //! - Type extensions //! //! ## The `ID` type //! //! The `ID` GraphQL type will be generated into [`juniper::ID`]. //! //! [`juniper::ID`]: https://docs.rs/juniper/latest/juniper/struct.ID.html //! //! ## Custom scalar types //! //! Custom scalar types will be generated into a newtype wrapper around a `String`. For example: //! //! ```graphql //! scalar Cursor //! ``` //! //! Would result in //! //! ``` //! pub struct Cursor(pub String); //! ``` //! //! ## Special case scalars //! //! A couple of scalar names have special meaning. Those are: //! //! - `Url` becomes //! [`url::Url`](https://docs.rs/url/2.1.0/url/struct.Url.html). //! - `Uuid` becomes //! [`uuid::Uuid`](https://docs.rs/uuid/0.7.4/uuid/struct.Uuid.html). //! - `Date` becomes //! [`chrono::naive::NaiveDate`](https://docs.rs/chrono/0.4.6/chrono/naive/struct.NaiveDate.html). //! - `DateTime` becomes [`chrono::DateTime<chrono::offset::Utc>`] by default but if defined with //! `scalar DateTime @juniper(with_time_zone: false)` it will become [`chrono::naive::NaiveDateTime`]. //! //! Juniper doesn't support [`chrono::Date`](https://docs.rs/chrono/0.4.9/chrono/struct.Date.html) //! so therefore this library cannot support that either. You can read about Juniper's supported //! integrations [here](https://docs.rs/juniper/0.13.1/juniper/integrations/index.html). //! //! [`chrono::DateTime<chrono::offset::Utc>`]: https://docs.rs/chrono/0.4.9/chrono/struct.DateTime.html //! [`chrono::naive::NaiveDateTime`]: https://docs.rs/chrono/0.4.9/chrono/naive/struct.NaiveDateTime.html //! //! ## Interfaces //! //! Juniper has several ways of representing GraphQL interfaces in Rust. They are listed //! [here](https://graphql-rust.github.io/types/interfaces.html#enums) along with their advantages //! and disadvantages. //! //! For the generated code we use the `enum` pattern because we found it to be the most flexible. //! //! Abbreviated example (find [complete example here](https://github.com/davidpdrsn/juniper-from-schema/blob/master/examples/interface.rs)): //! //! ``` //! # #[macro_use] //! # extern crate juniper; //! # use juniper::*; //! # use juniper_from_schema::graphql_schema; //! # fn main() {} //! # pub struct Context; //! # impl juniper::Context for Context {} //! # pub struct Article { id: ID, text: String } //! # impl ArticleFields for Article { //! # fn field_id( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&ID> { unimplemented!() } //! # fn field_text( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&String> { unimplemented!() } //! # } //! # pub struct Tweet { id: ID, text: String } //! # impl TweetFields for Tweet { //! # fn field_id( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&ID> { unimplemented!() } //! # fn field_text( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&String> { unimplemented!() } //! # } //! # //! graphql_schema! { //! schema { //! query: Query //! } //! //! type Query { //! search(query: String!): [SearchResult!]! @juniper(ownership: "owned") //! } //! //! 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, juniper_from_schema::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. //! //! Abbreviated example (find [complete example here](https://github.com/davidpdrsn/juniper-from-schema/blob/master/examples/union_types.rs)): //! //! ``` //! # #[macro_use] //! # extern crate juniper; //! # use juniper::*; //! # use juniper_from_schema::graphql_schema; //! # fn main() {} //! # pub struct Context; //! # impl juniper::Context for Context {} //! # pub struct Article { id: ID, text: String } //! # impl ArticleFields for Article { //! # fn field_id( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&ID> { unimplemented!() } //! # fn field_text( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&String> { unimplemented!() } //! # } //! # pub struct Tweet { id: ID, text: String } //! # impl TweetFields for Tweet { //! # fn field_id( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&ID> { unimplemented!() } //! # fn field_text( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&String> { unimplemented!() } //! # } //! # //! graphql_schema! { //! schema { //! query: Query //! } //! //! type Query { //! search(query: String!): [SearchResult!]! @juniper(ownership: "owned") //! } //! //! 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, juniper_from_schema::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. //! //! Abbreviated example (find [complete example here](https://github.com/davidpdrsn/juniper-from-schema/blob/master/examples/input_types.rs)): //! //! ``` //! # #[macro_use] //! # extern crate juniper; //! # use juniper::*; //! # use juniper_from_schema::graphql_schema; //! # fn main() {} //! # pub struct Context; //! # impl juniper::Context for Context {} //! # pub struct Post { id: ID } //! # impl PostFields for Post { //! # fn field_id( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&ID> { //! # unimplemented!() //! # } //! # fn field_title( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&String> { //! # unimplemented!() //! # } //! # } //! # pub struct Query; //! # impl QueryFields for Query { //! # fn field_noop( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&bool> { //! # unimplemented!() //! # } //! # } //! graphql_schema! { //! schema { //! query: Query //! mutation: Mutation //! } //! //! type Mutation { //! createPost(input: CreatePost!): Post @juniper(ownership: "owned") //! } //! //! 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, juniper_from_schema::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. //! //! Abbreviated example (find [complete example here](https://github.com/davidpdrsn/juniper-from-schema/blob/master/examples/enumeration_types.rs)): //! //! ``` //! # #[macro_use] //! # extern crate juniper; //! # use juniper::*; //! # use juniper_from_schema::graphql_schema; //! # fn main() {} //! # pub struct Context; //! # impl juniper::Context for Context {} //! # pub struct Post { id: ID } //! # impl PostFields for Post { //! # fn field_id( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&ID> { //! # Ok(&self.id) //! # } //! # } //! # //! graphql_schema! { //! schema { //! query: Query //! } //! //! enum Status { //! PUBLISHED //! UNPUBLISHED //! } //! //! type Query { //! allPosts(status: Status!): [Post!]! @juniper(ownership: "owned") //! } //! //! type Post { //! id: ID! //! } //! } //! //! pub struct Query; //! //! impl QueryFields for Query { //! fn field_all_posts( //! &self, //! executor: &Executor<'_, Context>, //! trail: &QueryTrail<'_, Post, juniper_from_schema::Walked>, //! status: Status, //! ) -> FieldResult<Vec<Post>> { //! match status { //! Status::Published => unimplemented!("find published posts"), //! Status::Unpublished => unimplemented!("find unpublished posts"), //! } //! } //! } //! ``` //! //! ## Default argument values //! //! In GraphQL you are able to provide default values for field arguments, provided the argument is //! nullable. //! //! Arguments of the following types support default values: //! - `Float` //! - `Int` //! - `String` //! - `Boolean` //! - Enumerations //! - Input objects (as field arguments, see below) //! - Lists containing some other supported type //! //! Abbreviated example (find [complete example here](https://github.com/davidpdrsn/juniper-from-schema/blob/master/examples/default_argument_values.rs)): //! //! ``` //! # #[macro_use] //! # extern crate juniper; //! # use juniper::*; //! # use juniper_from_schema::graphql_schema; //! # fn main() {} //! # pub struct Context; //! # impl juniper::Context for Context {} //! # pub struct Post { id: ID } //! # impl PostFields for Post { //! # fn field_id( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&ID> { //! # Ok(&self.id) //! # } //! # } //! # //! graphql_schema! { //! schema { //! query: Query //! } //! //! enum Status { //! PUBLISHED //! UNPUBLISHED //! } //! //! input Pagination { //! pageSize: Int! //! cursor: ID //! } //! //! type Query { //! allPosts( //! status: Status = PUBLISHED, //! pagination: Pagination = { pageSize: 20 } //! ): [Post!]! @juniper(ownership: "owned") //! } //! //! type Post { //! id: ID! //! } //! } //! //! pub struct Query; //! //! impl QueryFields for Query { //! fn field_all_posts( //! &self, //! executor: &Executor<'_, Context>, //! trail: &QueryTrail<'_, Post, juniper_from_schema::Walked>, //! status: Status, //! pagination: Pagination, //! ) -> FieldResult<Vec<Post>> { //! // `status` will be `Status::Published` if not given in the query //! //! match status { //! Status::Published => unimplemented!("find published posts"), //! Status::Unpublished => unimplemented!("find unpublished posts"), //! } //! } //! } //! ``` //! //! ### Input object gotchas //! //! Defaults for input objects are only supported as field arguments. The following is not //! supported //! //! ```graphql //! input SomeType { //! field: Int = 1 //! } //! ``` //! //! This isn't supported because [the spec is unclear about how to handle multiple nested //! defaults](https://github.com/webonyx/graphql-php/issues/350). //! //! Also, defaults are only used if no arguments are passed. So given the schema //! //! ```graphql //! input Input { //! a: String //! b: String //! } //! //! type Query { //! field(arg: Input = { a: "a" }): Int! //! } //! ``` //! //! and the query //! //! ```graphql //! query MyQuery { //! field(arg: { b: "my b" }) //! } //! ``` //! //! The value of `arg` inside the resolver would be `Input { a: None, b: Some("my b") }`. Note that //! even though `a` has a default value in the field doesn't get used here because we set `arg` in //! the query. //! //! # 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` -> [`juniper::ID`](https://docs.rs/juniper/latest/juniper/struct.ID.html) //! //! # 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 object types (non scalar values) will also get a `QueryTrail` argument //! besides the executor. //! //! Since the `QueryTrail` type itself is defined in this crate (rather than being inserted into //! your code) we cannot directly add methods for your GraphQL fields. Those methods have to be //! added through ["extension traits"](http://xion.io/post/code/rust-extension-traits.html). So if //! you see an error like //! //! ```text //! | trail.foo(); //! | ^^^ method not found in `&juniper_from_schema::QueryTrail<'a, User, juniper_from_schema::Walked>` //! | //! = help: items from traits can only be used if the trait is in scope //! help: the following trait is implemented but not in scope, perhaps add a `use` for it: //! | //! 2 | use crate::graphql_schema::query_trails::QueryTrailUserExtensions; //! | //! ``` //! //! Then adding `use crate::graphql_schema::query_trails::*` to you module should fix it. This is //! necessary because all the extention traits are generated inside a module called `query_trails`. //! This is done so you can glob import the `QueryTrail` extension traits without glob importing //! everything from your GraphQL schema. //! //! If you just want everything from the schema `use crate::graphql_schema::*` will also bring in //! the extension traits. //! //! [N+1 query bugs]: https://secure.phabricator.com/book/phabcontrib/article/n_plus_one/ //! [look ahead api]: https://docs.rs/juniper/0.11.1/juniper/struct.LookAheadSelection.html //! //! ## Abbreviated example //! //! Find [complete example here](https://github.com/davidpdrsn/juniper-from-schema/blob/master/examples/query_trails.rs) //! //! ``` //! # #[macro_use] //! # extern crate juniper; //! # use juniper::*; //! # use juniper_from_schema::graphql_schema; //! # fn main() {} //! # pub struct Context; //! # impl juniper::Context for Context {} //! # //! graphql_schema! { //! schema { //! query: Query //! } //! //! type Query { //! allPosts: [Post!]! @juniper(ownership: "owned") //! } //! //! 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, juniper_from_schema::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, juniper_from_schema::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<'a, T, K>`. `T` is the type the current //! field returns and `K` is either `Walked` or `NotWalked`. //! //! The lifetime `'a` comes from Juniper and is the lifetime of the incoming query. //! //! ### `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>`. //! //! If your field returns a `Vec<T>` or `Option<T>` the given query trail will be `QueryTrail<'_, //! T, _>`. So `Vec` or `Option` will be removed and you'll only be given the inner most type. //! That is because in the GraphQL query syntax it doesn't matter if you're querying a `User` //! or `[User]`. The fields you have access to are the same. //! //! ### `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: //! //! ```ignore //! 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. //! //! ## Downcasting for interface and union `QueryTrail`s //! //! _This section is mostly relevant if you're using //! [juniper-eager-loading](https://crates.io/crates/juniper-eager-loading) however it isn't //! specific to that library._ //! //! If you have a `QueryTrail<'a, T, Walked>` where `T` is an interface or union type you can use //! `.downcast()` to convert that `QueryTrail` into one of the implementors of the interface or //! union. //! //! Example: //! //! ``` //! # #[macro_use] //! # extern crate juniper; //! # use juniper::*; //! # use juniper_from_schema::graphql_schema; //! # fn main() {} //! # pub struct Context; //! # impl juniper::Context for Context {} //! # pub struct Article { id: ID } //! # impl ArticleFields for Article { //! # fn field_id( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&ID> { unimplemented!() } //! # } //! # pub struct Tweet { id: ID, text: String } //! # impl TweetFields for Tweet { //! # fn field_id( //! # &self, //! # executor: &Executor<'_, Context>, //! # ) -> FieldResult<&ID> { unimplemented!() } //! # } //! # //! graphql_schema! { //! schema { //! query: Query //! } //! //! type Query { //! search(query: String!): [SearchResult!]! //! } //! //! interface SearchResult { //! id: ID! //! } //! //! type Article implements SearchResult { //! id: ID! //! } //! //! type Tweet implements SearchResult { //! id: ID! //! } //! } //! //! pub struct Query; //! //! impl QueryFields for Query { //! fn field_search( //! &self, //! executor: &Executor<'_, Context>, //! trail: &QueryTrail<'_, SearchResult, juniper_from_schema::Walked>, //! query: String, //! ) -> FieldResult<&Vec<SearchResult>> { //! let article_trail: QueryTrail<'_, Article, Walked> = trail.downcast(); //! let tweet_trail: QueryTrail<'_, Tweet, Walked> = trail.downcast(); //! //! // ... //! # unimplemented!() //! } //! } //! ``` //! //! ### Why is this useful? //! //! If you were do perform some kind of preloading of data you might have a function that inspects //! a `QueryTrail` and loads the necessary data from a database. Such a function could look like //! this: //! //! ```ignore //! fn preload_users( //! mut users: Vec<User>, //! query_trail: &QueryTrail<'_, User, Walked>, //! db: &Database, //! ) -> Vec<User> { //! // ... //! } //! ``` //! //! This function works well when we have field that returns `[User!]!`. That field is going to get //! a `QueryTrail<'a, User, Walked>` which is exactly what `preload_users` needs. //! //! However, now imagine you have a schema like this: //! //! ```graphql //! type Query { //! search(query: String!): [SearchResult!]! //! } //! //! union SearchResult = User | City | Country //! //! type User { //! id: ID! //! city: City! //! } //! //! type City { //! id: ID! //! country: Country! //! } //! //! type Country { //! id: ID! //! } //! ``` //! //! The method `QueryFields::field_search` will receive a `QueryTrail<'a, SearchResult, Walked>`. //! That type doesn't work with `preload_users`. So we have to convert our `QueryTrail<'a, //! SearchResult, Walked>` into `QueryTrail<'a, User, Walked>`. //! //! This can be done by calling `.downcast()` which automatically gets implemented for interface and //! union query trails. See above for an example. //! //! # Customizing the error type //! //! By default the return type of the generated field methods will be [`juniper::FieldResult<T>`]. //! That is just a type alias for `std::result::Result<T, juniper::FieldError>`. Should you want to //! use a different error type than [`juniper::FieldError`] that can be done by passing `, //! error_type: YourType` to [`graphql_schema_from_file!`]. //! //! Just keep in that your custom error type must implement [`juniper::IntoFieldError`] to //! type check. //! //! Example: //! //! ``` //! # #[macro_use] //! # extern crate juniper; //! # use juniper::*; //! # use juniper_from_schema::graphql_schema_from_file; //! # fn main() {} //! # pub struct Context; //! # impl juniper::Context for Context {} //! # pub struct Mutation; //! # impl MutationFields for Mutation { //! # fn field_noop(&self, executor: &Executor<'_, Context>) -> Result<&bool, MyError> { //! # Ok(&true) //! # } //! # } //! graphql_schema_from_file!("tests/schemas/doc_schema.graphql", error_type: MyError); //! //! pub struct MyError(String); //! //! impl juniper::IntoFieldError for MyError { //! fn into_field_error(self) -> juniper::FieldError { //! // Perform custom error handling //! juniper::FieldError::from(self.0) //! } //! } //! //! pub struct Query; //! //! impl QueryFields for Query { //! fn field_hello_world( //! &self, //! executor: &Executor<'_, Context>, //! name: String, //! ) -> Result<String, MyError> { //! Ok(format!("Hello, {}!", name)) //! } //! } //! ``` //! //! [`graphql_schema!`] does not support changing the error type. //! //! [`graphql_schema!`]: macro.graphql_schema.html //! [`graphql_schema_from_file!`]: macro.graphql_schema_from_file.html //! [`juniper::IntoFieldError`]: https://docs.rs/juniper/0.11.1/juniper/trait.IntoFieldError.html //! [`juniper::FieldError`]: https://docs.rs/juniper/0.11.1/juniper/struct.FieldError.html //! [`juniper::FieldResult<T>`]: https://docs.rs/juniper/0.11.1/juniper/type.FieldResult.html //! //! # Customizing the context type //! //! By default the generate code will assume your context type is called `Context`. If that is not //! the case you can customize it by calling [`graphql_schema_from_file!`] with `context_type: NewName`. //! //! Example: //! //! ``` //! # #[macro_use] //! # extern crate juniper; //! # use juniper::*; //! # use juniper_from_schema::graphql_schema_from_file; //! # fn main() {} //! # pub struct Mutation; //! # impl MutationFields for Mutation { //! # fn field_noop(&self, executor: &Executor<'_, MyContext>) -> juniper::FieldResult<&bool> { //! # Ok(&true) //! # } //! # } //! graphql_schema_from_file!("tests/schemas/doc_schema.graphql", context_type: MyContext); //! //! pub struct MyContext; //! impl juniper::Context for MyContext {} //! //! pub struct Query; //! //! impl QueryFields for Query { //! fn field_hello_world( //! &self, //! executor: &Executor<'_, MyContext>, //! name: String, //! ) -> juniper::FieldResult<String> { //! Ok(format!("Hello, {}!", name)) //! } //! } //! ``` //! //! [`graphql_schema!`] does not support changing the context type. //! //! [`graphql_schema!`]: macro.graphql_schema.html //! [`graphql_schema_from_file!`]: macro.graphql_schema_from_file.html //! //! # Inspecting the generated code //! //! If you wish to see exactly what code gets generated you can set the env var //! `JUNIPER_FROM_SCHEMA_DEBUG` to `1` when compiling. For example: //! //! ```bash //! JUNIPER_FROM_SCHEMA_DEBUG=1 cargo build //! ``` //! //! The code will not be formatted so it might be tricky to read. The easiest way to fix this is to //! copy the printed code to a file and run it through [rustfmt]. //! //! Alternatively you can include the [feature] called `"format-debug-output"`. This will run the //! output through [rustfmt] before printing it. That way you don't have to do that manually. //! Example `Cargo.toml`: //! //! ```toml //! [dependencies] //! juniper-from-schema = { version = "x.y.z", features = ["format-debug-output"] } //! ``` //! //! Unfortunately this requires that you're using nightly, because [rustfmt requires //! nightly](https://github.com/rust-lang/rustfmt#installing-from-source). It might also break your //! build because [rustfmt] doesn't always compile for some reason ¯\\\_(ツ)\_/¯. If you experience //! this just remove the `"format-debug-output"` feature and format the output manually. //! //! [feature]: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#choosing-features //! [rustfmt]: https://github.com/rust-lang/rustfmt #![deny( missing_docs, unused_imports, dead_code, unused_variables, unused_must_use )] #![doc(html_root_url = "https://docs.rs/juniper-from-schema/0.4.0")] use juniper::{DefaultScalarValue, LookAheadSelection}; use std::marker::PhantomData; pub use juniper_from_schema_code_gen::{graphql_schema, graphql_schema_from_file}; /// A type used to parameterize `QueryTrail` to know that `walk` has been called. pub struct Walked; /// A type used to parameterize `QueryTrail` to know that `walk` has *not* been called. pub struct NotWalked; /// A wrapper around a `juniper::LookAheadSelection` with methods for each possible child. pub struct QueryTrail<'a, T, K> { #[doc(hidden)] pub look_ahead: Option<&'a LookAheadSelection<'a, DefaultScalarValue>>, #[doc(hidden)] pub node_type: PhantomData<T>, #[doc(hidden)] pub walked: K, } impl<'a, T> QueryTrail<'a, T, NotWalked> { /// Check if the trail is present in the query being executed pub fn walk(self) -> Option<QueryTrail<'a, T, Walked>> { match self.look_ahead { Some(inner) => Some(QueryTrail { look_ahead: Some(inner), node_type: self.node_type, walked: Walked, }), None => None, } } } /// Make a `QueryTrail` from something, normally a `juniper::LookAheadSelection`. /// /// You normally shouldn't need to worry about this trait. pub trait MakeQueryTrail<'a> { #[allow(missing_docs)] fn make_query_trail<T>(&'a self) -> QueryTrail<'a, T, Walked>; } impl<'a> MakeQueryTrail<'a> for LookAheadSelection<'a, DefaultScalarValue> { fn make_query_trail<T>(&'a self) -> QueryTrail<'a, T, Walked> { QueryTrail { look_ahead: Some(self), node_type: PhantomData, walked: Walked, } } } #[cfg(test)] mod test { #[allow(unused_imports)] use super::*; #[rustversion::nightly] #[test] fn test_compile_pass() { let t = trybuild::TestCases::new(); t.pass("tests/compile_pass/*.rs"); t.compile_fail("tests/compile_fail/*.rs"); } }