[−][src]Crate juniper_from_schema
This library contains 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 involved in using Juniper.
Table of contents
- Example
- Example web app
- Customizing ownership
- GraphQL features
- GraphQL to Rust types
- Query trails
- Customizing the error type
- Customizing the context type
- Inspecting the generated code
Example
Schema:
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.
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 fromself
(FieldResult<&T>
).@juniper(ownership: "owned")
: The return type will be owned (FieldResult<T>
).@juniper(ownership: "as_ref")
: Only applicable forOption
andVec
return types. Changes the inner type to be borrowed (FieldResult<Option<&T>>
orFieldResult<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
.
Custom scalar types
Custom scalar types will be generated into a newtype wrapper around a String
. For example:
scalar Cursor
Would result in
pub struct Cursor(pub String);
Special case scalars
A couple of scalar names have special meaning. Those are:
Url
becomesurl::Url
.Uuid
becomesuuid::Uuid
.Date
becomeschrono::naive::NaiveDate
.DateTime
becomeschrono::DateTime<chrono::offset::Utc>
by default but if defined withscalar DateTime @juniper(with_time_zone: false)
it will becomechrono::naive::NaiveDateTime
.
Juniper doesn't support chrono::Date
so therefore this library cannot support that either. You can read about Juniper's supported
integrations here.
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.
Abbreviated example (find complete example here):
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):
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):
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):
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):
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
input SomeType {
field: Int = 1
}
This isn't supported because the spec is unclear about how to handle multiple nested defaults.
Also, defaults are only used if no arguments are passed. So given the schema
input Input {
a: String
b: String
}
type Query {
field(arg: Input = { a: "a" }): Int!
}
and the query
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
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". So if
you see an error like
| 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.
Abbreviated example
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:
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 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:
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(); // ... } }
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:
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:
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:
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.
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:
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.
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:
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
:
[dependencies]
juniper-from-schema = { version = "x.y.z", features = ["format-debug-output"] }
Unfortunately this requires that you're using nightly, because rustfmt requires
nightly. 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.
Macros
graphql_schema | Write your GraphQL schema directly in your Rust code. |
graphql_schema_from_file | Read a GraphQL schema file and generate corresponding Juniper macro calls. |
Structs
NotWalked | A type used to parameterize |
QueryTrail | A wrapper around a |
Walked | A type used to parameterize |
Traits
MakeQueryTrail | Make a |