GraphQLType is not satisfied with juniper::object

[jasonlor]

Currently using 0.14.1. I'm attempting to implement fields with the juniper::object macro.

#[juniper::object(
    Context = Context,
    Scalar = juniper::DefaultScalarValue,
)]
impl Event {

On compilation, i see the following error:
error[E0277]: the trait bound models::Event: juniper::GraphQLType<__S> is not satisfied

On this struct, I've implemented another trait that does not have the juniper::object macro.
impl TraitName for Event

I've looked through the docs and issues and have been unable to find a solution.

Thanks!

[davidpdrsn]

Are you able to share a minimal reproduction script? It’s a bit hard to say what’s wrong from what you posted.

[andy128k]

I have found similar issue. Here is minimal example which fails to build.

[jasonlor]

Bump, any ideas?

[RyuuGan]

Hello,

Any updates on this ?

#[derive(GraphQLObject)]
          ^^^^^^^^^^^^^ the trait `juniper::types::base::GraphQLType<__S>` is not implemented for `api::graphql::projects::GQLProject`

I also trying to use it as in @andy128k example

[RyuuGan]

Hello,

I found a workaround, so it will compile and work as expected. The idea is that you don't use #[juniper::object] inside the #[derive(GraphQLObject)], but what you can do is define all objects as #[juniper::object]. Yes it is a little bit ugly to define all the methods, but at least it works.

So instead of:

pub struct Article {
    pub title: String,
}

#[juniper::object(name = "Article")]
impl Article {
    fn title(&self) -> &str { &self.title }
}

#[derive(juniper::GraphQLObject)]
pub struct Blog {
    pub url: String,
    pub description: Vec<String>,
    pub articles: Vec<Article>,
}

You define:

pub struct Article {
    pub title: String,
}

#[juniper::object(name = "Article")]
impl Article {
    fn title(&self) -> &str { &self.title }
}

pub struct Blog {
    pub url: String,
    pub description: Vec<String>,
    pub articles: Vec<Article>,
}

#[juniper::object(name = "Blog")]
impl Blog {
  // ...
}

[zhenwenc]

@andy128k @RyuuGan Have you tried adding the scalar attribute to derived([GraphQLObject])?

#[derive(juniper::GraphQLObject)]
#[graphql(scalar = juniper::DefaultScalarValue)]
pub struct Blog {
    pub url: String,
    pub description: Vec<String>,
    pub articles: Vec<Article>,
}

For some reason it is required, otherwise generic will be used instead of the DefaultScalarValue:

juniper/juniper_codegen/src/util.rs

Lines 734 to 740 in eddf948

	if self.generic_scalar {
	// If generic_scalar is true, we always insert a generic scalar.
	// See more comments below.
	quote!(__S)
	} else {
	quote!(#juniper_crate_name::DefaultScalarValue)
	}

since generic_scalar has been set to true when deriving GraphQLObject:

juniper/juniper_codegen/src/derive_object.rs

Line 76 in eddf948

generic_scalar: true,

Not sure if this is a bug or by design. 🤔

[urkle]

I'm running into this issue as well when trying to use juniper::graphql_union! against two object where I used #[juniper::object] on an impl.

pub struct MyObject {
  id: i32,
}

#[juniper::object]
impl MyObject {
  fn id(&self) -> i32 {
    &self.id
  }
}

enum MyUnion {
  MyObject(MyObject),
}

juniper::graphql_union!(MyUnion: () where Scalar = <S> |&self| {
    instance_resolvers: |_| {
        &MyObject => match *self { MyUnion::MyObject(ref h) => Some(h), _ => None },
    }
});

This results with

error[E0277]: the trait bound `MyObject: juniper::types::base::GraphQLType<S>` is not satisfied
  --> src/my_object.rs:8:1
   |
8  | / juniper::graphql_union!(MyUnion: () where Scalar = <S> |&self| {
9  | |     instance_resolvers: |_| {
10 | |         &MyObject => match *self { MyUnion::MyObject(ref h) => Some(h), _ => None },
12 | |     }
13 | | });
   | |___^ the trait `juniper::types::base::GraphQLType<S>` is not implemented for `MyObject`

[tyranron]

@urkle I guess that's because GraphQLType implementtion for MyObject is not generic over ScalarValue, while you're trying to do so for MyUnion.

Try this:

juniper::graphql_union!(MyUnion: () where Scalar = juniper::DefaultScalarValue |&self| {

Also, cargo expand will show more why this happens.

[urkle]

@tyranron Awesome Thanks! That fixed the issue.