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< ol class = "chapter" > < li class = "chapter-item expanded " > < a href = "../index.html" > < strong aria-hidden = "true" > 1.< / strong > Introduction< / a > < / li > < li class = "chapter-item expanded " > < a href = "../quickstart.html" > < strong aria-hidden = "true" > 2.< / strong > Quickstart< / a > < / li > < li class = "chapter-item expanded " > < a href = "../types/index.html" > < strong aria-hidden = "true" > 3.< / strong > Type System< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../types/objects/defining_objects.html" > < strong aria-hidden = "true" > 3.1.< / strong > Defining objects< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../types/objects/complex_fields.html" > < strong aria-hidden = "true" > 3.1.1.< / strong > Complex fields< / a > < / li > < li class = "chapter-item expanded " > < a href = "../types/objects/using_contexts.html" > < strong aria-hidden = "true" > 3.1.2.< / strong > Using contexts< / a > < / li > < li class = "chapter-item expanded " > < a href = "../types/objects/error_handling.html" > < strong aria-hidden = "true" > 3.1.3.< / strong > Error handling< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../types/other-index.html" > < strong aria-hidden = "true" > 3.2.< / strong > Other types< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../types/enums.html" > < strong aria-hidden = "true" > 3.2.1.< / strong > Enums< / a > < / li > < li class = "chapter-item expanded " > < a href = "../types/interfaces.html" class = "active" > < strong aria-hidden = "true" > 3.2.2.< / strong > Interfaces< / a > < / li > < li class = "chapter-item expanded " > < a href = "../types/input_objects.html" > < strong aria-hidden = "true" > 3.2.3.< / strong > Input objects< / a > < / li > < li class = "chapter-item expanded " > < a href = "../types/scalars.html" > < strong aria-hidden = "true" > 3.2.4.< / strong > Scalars< / a > < / li > < li class = "chapter-item expanded " > < a href = "../types/unions.html" > < strong aria-hidden = "true" > 3.2.5.< / strong > Unions< / a > < / li > < / ol > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../schema/schemas_and_mutations.html" > < strong aria-hidden = "true" > 4.< / strong > Schemas and mutations< / a > < / li > < li class = "chapter-item expanded " > < a href = "../servers/index.html" > < strong aria-hidden = "true" > 5.< / strong > Adding A Server< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../servers/official.html" > < strong aria-hidden = "true" > 5.1.< / strong > Official Server Integrations< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../servers/warp.html" > < strong aria-hidden = "true" > 5.1.1.< / strong > Warp< / a > < / li > < li class = "chapter-item expanded " > < a href = "../servers/rocket.html" > < strong aria-hidden = "true" > 5.1.2.< / strong > Rocket< / a > < / li > < li class = "chapter-item expanded " > < a href = "../servers/iron.html" > < strong aria-hidden = "true" > 5.1.3.< / strong > Iron< / a > < / li > < li class = "chapter-item expanded " > < a href = "../servers/hyper.html" > < strong aria-hidden = "true" > 5.1.4.< / strong > Hyper< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../servers/third-party.html" > < strong aria-hidden = "true" > 5.2.< / strong > Third Party Integrations< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../advanced/index.html" > < strong aria-hidden = "true" > 6.< / strong > Advanced Topics< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../advanced/introspection.html" > < strong aria-hidden = "true" > 6.1.< / strong > Introspection< / a > < / li > < li class = "chapter-item expanded " > < a href = "../advanced/non_struct_objects.html" > < strong aria-hidden = "true" > 6.2.< / strong > Non-struct objects< / a > < / li > < li class = "chapter-item expanded " > < a href = "../advanced/implicit_and_explicit_null.html" > < strong aria-hidden = "true" > 6.3.< / strong > Implicit and explicit null< / a > < / li > < li class = "chapter-item expanded " > < a href = "../advanced/objects_and_generics.html" > < strong aria-hidden = "true" > 6.4.< / strong > Objects and generics< / a > < / li > < li class = "chapter-item expanded " > < a href = "../advanced/multiple_ops_per_request.html" > < strong aria-hidden = "true" > 6.5.< / strong > Multiple operations per request< / a > < / li > < li class = "chapter-item expanded " > < a href = "../advanced/dataloaders.html" > < strong aria-hidden = "true" > 6.6.< / strong > Dataloaders< / a > < / li > < li cla
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< h1 id = "interfaces" > < a class = "header" href = "#interfaces" > Interfaces< / a > < / h1 >
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< p > < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interfaces< / a > map well to interfaces known from common object-oriented languages such as Java or C#, but Rust, unfortunately, has no concept that maps perfectly to them. The nearest analogue of < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interfaces< / a > are Rust traits, and the main difference is that in GraphQL an < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > interface type< / a > serves both as an < em > abstraction< / em > and a < em > boxed value (downcastable to concrete implementers)< / em > , while in Rust, a trait is an < em > abstraction only< / em > and < em > to represent such a boxed value a separate type is required< / em > , like enum or trait object, because Rust trait doesn't represent a type itself, and so can have no values. This difference imposes some unintuitive and non-obvious corner cases when we try to express < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interfaces< / a > in Rust, but on the other hand gives you full control over which type is backing your interface, and how it's resolved.< / p >
< p > For implementing < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interfaces< / a > Juniper provides the < code > #[graphql_interface]< / code > macro.< / p >
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< h2 id = "traits" > < a class = "header" href = "#traits" > Traits< / a > < / h2 >
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< p > Defining a trait is mandatory for defining a < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interface< / a > , because this is the < em > obvious< / em > way we describe an < em > abstraction< / em > in Rust. All < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > interface< / a > fields are defined as computed ones via trait methods.< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > use juniper::graphql_interface;
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#[graphql_interface]
trait Character {
fn id(& self) -> & str;
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< p > However, to return values of such < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > interface< / a > , we should provide its implementers and the Rust type representing a < em > boxed value of this trait< / em > . The last one can be represented in two flavors: enum and < a href = "https://doc.rust-lang.org/reference/types/trait-object.html" > trait object< / a > .< / p >
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< h3 id = "enum-values-default" > < a class = "header" href = "#enum-values-default" > Enum values (default)< / a > < / h3 >
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< p > By default, Juniper generates an enum representing the values of the defined < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interface< / a > , and names it straightforwardly, < code > {Interface}Value< / code > .< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > use juniper::{graphql_interface, GraphQLObject};
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#[graphql_interface(for = [Human, Droid])] // enumerating all implementers is mandatory
trait Character {
fn id(& self) -> & str;
}
#[derive(GraphQLObject)]
#[graphql(impl = CharacterValue)] // notice enum name, NOT trait name
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struct Human {
id: String,
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}
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#[derive(GraphQLObject)]
#[graphql(impl = CharacterValue)]
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struct Droid {
id: String,
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}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< p > Also, enum name can be specified explicitly, if desired.< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > use juniper::{graphql_interface, GraphQLObject};
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#[graphql_interface(enum = CharaterInterface, for = Human)]
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trait Character {
fn id(& self) -> & str;
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}
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#[derive(GraphQLObject)]
#[graphql(impl = CharaterInterface)]
struct Human {
id: String,
home_planet: String,
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< h3 id = "interfaces-implementing-other-interfaces" > < a class = "header" href = "#interfaces-implementing-other-interfaces" > Interfaces implementing other interfaces< / a > < / h3 >
< p > GraphQL allows implementing interfaces on other interfaces in addition to objects.< / p >
< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > use juniper::{graphql_interface, graphql_object, ID};
#[graphql_interface(for = [HumanValue, Luke])]
struct Node {
id: ID,
}
#[graphql_interface(impl = NodeValue, for = Luke)]
struct Human {
id: ID,
home_planet: String,
}
struct Luke {
id: ID,
}
#[graphql_object(impl = [HumanValue, NodeValue])]
impl Luke {
fn id(& self) -> & ID {
& self.id
}
// As `String` and `& str` aren't distinguished by
// GraphQL spec, you can use them interchangeably.
// Same is applied for `Cow< 'a, str> `.
// ⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄
fn home_planet() -> & 'static str {
" Tatooine"
}
}
< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< blockquote >
< p > < strong > NOTE:< / strong > Every interface has to specify all other interfaces/objects it implements or implemented for. Missing one of < code > for = < / code > or < code > impl = < / code > attributes is a compile-time error.< / p >
< / blockquote >
< pre > < code class = "language-compile_fail" > # extern crate juniper;
use juniper::{graphql_interface, GraphQLObject};
#[derive(GraphQLObject)]
pub struct ObjA {
id: String,
}
#[graphql_interface(for = ObjA)]
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at
// 'Failed to implement interface `Character` on `ObjA`: missing interface reference in implementer's `impl` attribute.'
struct Character {
id: String,
}
fn main() {}
< / code > < / pre >
< h3 id = "graphql-subtyping-and-additional-nullable-fields" > < a class = "header" href = "#graphql-subtyping-and-additional-nullable-fields" > GraphQL subtyping and additional < code > null< / code > able fields< / a > < / h3 >
< p > GraphQL allows implementers (both objects and other interfaces) to return " subtypes" instead of an original value. Basically, this allows you to impose additional bounds on the implementation.< / p >
< p > Valid " subtypes" are:< / p >
< ul >
< li > interface implementer instead of an interface itself:
< ul >
< li > < code > I implements T< / code > in place of a < code > T< / code > ;< / li >
< li > < code > Vec< I implements T> < / code > in place of a < code > Vec< T> < / code > .< / li >
< / ul >
< / li >
< li > non-null value in place of a nullable:
< ul >
< li > < code > T< / code > in place of a < code > Option< T> < / code > ;< / li >
< li > < code > Vec< T> < / code > in place of a < code > Vec< Option< T> > < / code > .< / li >
< / ul >
< / li >
< / ul >
< p > These rules are recursively applied, so < code > Vec< Vec< I implements T> > < / code > is a valid " subtype" of a < code > Option< Vec< Option< Vec< Option< T> > > > > < / code > .< / p >
< p > Also, GraphQL allows implementers to add < code > null< / code > able fields, which aren't present on an original interface.< / p >
< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > use juniper::{graphql_interface, graphql_object, ID};
#[graphql_interface(for = [HumanValue, Luke])]
struct Node {
id: ID,
}
#[graphql_interface(for = HumanConnectionValue)]
struct Connection {
nodes: Vec< NodeValue> ,
}
#[graphql_interface(impl = NodeValue, for = Luke)]
struct Human {
id: ID,
home_planet: String,
}
#[graphql_interface(impl = ConnectionValue)]
struct HumanConnection {
nodes: Vec< HumanValue> ,
// ^^^^^^^^^^ notice not `NodeValue`
// This can happen, because every `Human` is a `Node` too, so we are just
// imposing additional bounds, which still can be resolved with
// `... on Connection { nodes }`.
}
struct Luke {
id: ID,
}
#[graphql_object(impl = [HumanValue, NodeValue])]
impl Luke {
fn id(& self) -> & ID {
& self.id
}
fn home_planet(language: Option< String> ) -> & 'static str {
// ^^^^^^^^^^^^^^
// Notice additional `null`able field, which is missing on `Human`.
// Resolving `...on Human { homePlanet }` will provide `None` for this
// argument.
match language.as_deref() {
None | Some(" en" ) => " Tatooine" ,
Some(" ko" ) => " 타투인" ,
_ => todo!(),
}
}
}
< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< p > Violating GraphQL " subtyping" or additional nullable field rules is a compile-time error.< / p >
< pre > < code class = "language-compile_fail" > # extern crate juniper;
use juniper::{graphql_interface, graphql_object};
pub struct ObjA {
id: String,
}
#[graphql_object(impl = CharacterValue)]
impl ObjA {
fn id(& self, is_present: bool) -> & str {
// ^^ the evaluated program panicked at
// 'Failed to implement interface `Character` on `ObjA`: Field `id`: Argument `isPresent` of type `Boolean!`
// isn't present on the interface and so has to be nullable.'
is_present.then(|| self.id.as_str()).unwrap_or(" missing" )
}
}
#[graphql_interface(for = ObjA)]
struct Character {
id: String,
}
#
# fn main() {}
< / code > < / pre >
< pre > < code class = "language-compile_fail" > # extern crate juniper;
use juniper::{graphql_interface, GraphQLObject};
#[derive(GraphQLObject)]
#[graphql(impl = CharacterValue)]
pub struct ObjA {
id: Vec< String> ,
// ^^ the evaluated program panicked at
// 'Failed to implement interface `Character` on `ObjA`: Field `id`: implementor is expected to return a subtype of
// interface's return object: `[String!]!` is not a subtype of `String!`.'
}
#[graphql_interface(for = ObjA)]
struct Character {
id: String,
}
#
# fn main() {}
< / code > < / pre >
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< h3 id = "ignoring-trait-methods" > < a class = "header" href = "#ignoring-trait-methods" > Ignoring trait methods< / a > < / h3 >
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< p > We may want to omit some trait methods to be assumed as < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interface< / a > fields and ignore them.< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > use juniper::{graphql_interface, GraphQLObject};
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#[graphql_interface(for = Human)]
trait Character {
fn id(& self) -> & str;
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#[graphql(ignore)] // or `#[graphql(skip)]`, your choice
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fn ignored(& self) -> u32 { 0 }
}
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#[derive(GraphQLObject)]
#[graphql(impl = CharacterValue)]
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struct Human {
id: String,
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< h3 id = "fields-arguments-and-interface-customization" > < a class = "header" href = "#fields-arguments-and-interface-customization" > Fields, arguments and interface customization< / a > < / h3 >
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< p > Similarly to < a href = "https://spec.graphql.org/October2021#sec-Objects" > GraphQL objects< / a > Juniper allows to fully customize < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > interface< / a > fields and their arguments.< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > #![allow(deprecated)]
< / span > < span class = "boring" > extern crate juniper;
< / span > use juniper::graphql_interface;
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// Renames the interface in GraphQL schema.
#[graphql_interface(name = " MyCharacter" )]
// Describes the interface in GraphQL schema.
#[graphql_interface(description = " My own character." )]
// Usual Rust docs are supported too as GraphQL interface description,
// but `description` attribute argument takes precedence over them, if specified.
/// This doc is absent in GraphQL schema.
trait Character {
// Renames the field in GraphQL schema.
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#[graphql(name = " myId" )]
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// Deprecates the field in GraphQL schema.
// Usual Rust `#[deprecated]` attribute is supported too as field deprecation,
// but `deprecated` attribute argument takes precedence over it, if specified.
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#[graphql(deprecated = " Do not use it." )]
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// Describes the field in GraphQL schema.
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#[graphql(description = " ID of my own character." )]
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// Usual Rust docs are supported too as field description,
// but `description` attribute argument takes precedence over them, if specified.
/// This description is absent in GraphQL schema.
fn id(
& self,
// Renames the argument in GraphQL schema.
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#[graphql(name = " myNum" )]
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// Describes the argument in GraphQL schema.
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#[graphql(description = " ID number of my own character." )]
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// Specifies the default value for the argument.
// The concrete value may be omitted, and the `Default::default` one
// will be used in such case.
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#[graphql(default = 5)]
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num: i32,
) -> & str;
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< p > Renaming policies for all < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interface< / a > fields and arguments are supported as well:< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > #![allow(deprecated)]
< / span > < span class = "boring" > extern crate juniper;
< / span > use juniper::graphql_interface;
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#[graphql_interface(rename_all = " none" )] // disables any renaming
trait Character {
// Now exposed as `my_id` and `my_num` in the schema
fn my_id(& self, my_num: i32) -> & str;
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< h3 id = "custom-context" > < a class = "header" href = "#custom-context" > Custom context< / a > < / h3 >
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< p > If a < a href = "https://docs.rs/juniper/0.14.2/juniper/trait.Context.html" > < code > Context< / code > < / a > is required in a trait method to resolve a < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interface< / a > field, specify it as an argument.< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > < span class = "boring" > use std::collections::HashMap;
< / span > use juniper::{graphql_interface, GraphQLObject};
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struct Database {
humans: HashMap< String, Human> ,
}
impl juniper::Context for Database {}
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#[graphql_interface(for = Human)] // look, ma, context type is inferred! ＼ ／
trait Character { // while still can be specified via `Context = ...` attribute argument
// If a field argument is named `context` or `ctx`, it's automatically assumed
// as a context argument.
fn id(& self, context: & Database) -> Option< & str> ;
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// Otherwise, you may mark it explicitly as a context argument.
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fn name(& self, #[graphql(context)] db: & Database) -> Option< & str> ;
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}
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#[derive(GraphQLObject)]
#[graphql(impl = CharacterValue, Context = Database)]
struct Human {
id: String,
name: String,
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}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< h3 id = "using-executor-and-explicit-generic-scalar" > < a class = "header" href = "#using-executor-and-explicit-generic-scalar" > Using executor and explicit generic scalar< / a > < / h3 >
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< p > If an < a href = "https://docs.rs/juniper/latest/juniper/struct.Executor.html" > < code > Executor< / code > < / a > is required in a trait method to resolve a < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interface< / a > field, specify it as an argument.< / p >
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< p > This requires to explicitly parametrize over < a href = "https://docs.rs/juniper/latest/juniper/trait.ScalarValue.html" > < code > ScalarValue< / code > < / a > , as < a href = "https://docs.rs/juniper/latest/juniper/struct.Executor.html" > < code > Executor< / code > < / a > does so. < / p >
< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > use juniper::{graphql_interface, graphql_object, Executor, LookAheadMethods as _, ScalarValue};
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#[graphql_interface(for = Human, Scalar = S)] // notice specifying `ScalarValue` as existing type parameter
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trait Character< S: ScalarValue> {
// If a field argument is named `executor`, it's automatically assumed
// as an executor argument.
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fn id< 'a> (& self, executor: & 'a Executor< '_, '_, (), S> ) -> & 'a str;
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// Otherwise, you may mark it explicitly as an executor argument.
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fn name< 'b> (
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& 'b self,
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#[graphql(executor)] another: & Executor< '_, '_, (), S> ,
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) -> & 'b str;
fn home_planet(& self) -> & str;
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}
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struct Human {
id: String,
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name: String,
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home_planet: String,
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}
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#[graphql_object(scalar = S: ScalarValue, impl = CharacterValue< S> )]
impl Human {
async fn id< 'a, S> (& self, executor: & 'a Executor< '_, '_, (), S> ) -> & 'a str
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where
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S: ScalarValue,
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{
executor.look_ahead().field_name()
}
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async fn name< 'b, S> (& 'b self, #[graphql(executor)] _: & Executor< '_, '_, (), S> ) -> & 'b str {
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& self.name
}
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fn home_planet< 'c, S> (& 'c self, #[graphql(executor)] _: & Executor< '_, '_, (), S> ) -> & 'c str {
// Executor may not be present on the trait method ^^^^^^^^^^^^^^^^^^^^^^^^
& self.home_planet
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}
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}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< h2 id = "scalarvalue-considerations" > < a class = "header" href = "#scalarvalue-considerations" > < code > ScalarValue< / code > considerations< / a > < / h2 >
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< p > By default, < code > #[graphql_interface]< / code > macro generates code, which is generic over a < a href = "https://docs.rs/juniper/latest/juniper/trait.ScalarValue.html" > < code > ScalarValue< / code > < / a > type. This may introduce a problem when at least one of < a href = "https://spec.graphql.org/October2021#sec-Interfaces" > GraphQL interface< / a > implementers is restricted to a concrete < a href = "https://docs.rs/juniper/latest/juniper/trait.ScalarValue.html" > < code > ScalarValue< / code > < / a > type in its implementation. To resolve such problem, a concrete < a href = "https://docs.rs/juniper/latest/juniper/trait.ScalarValue.html" > < code > ScalarValue< / code > < / a > type should be specified.< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > use juniper::{graphql_interface, DefaultScalarValue, GraphQLObject};
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#[graphql_interface(for = [Human, Droid])]
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#[graphql_interface(scalar = DefaultScalarValue)] // removing this line will fail compilation
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trait Character {
fn id(& self) -> & str;
}
#[derive(GraphQLObject)]
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#[graphql(impl = CharacterValue, Scalar = DefaultScalarValue)]
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struct Human {
id: String,
home_planet: String,
}
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#[derive(GraphQLObject)]
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#[graphql(impl = CharacterValue, Scalar = DefaultScalarValue)]
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struct Droid {
id: String,
primary_function: String,
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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