1.1 KiB
1.1 KiB
Custom directive
Async-graphql
can easily customize directives, which can extend the behavior of GraphQL.
To create a custom directive, you need to implement the CustomDirective
trait, and then use the Directive
macro to
generate a factory function that receives the parameters of the directive and returns an instance of the directive.
Currently Async-graphql
only supports directive located at FIELD
.
struct ConcatDirective {
value: String,
}
#[async_trait::async_trait]
impl CustomDirective for ConcatDirective {
async fn resolve_field(&self, _ctx: &Context<'_>, resolve: ResolveFut<'_>) -> ServerResult<Option<Value>> {
resolve.await.map(|value| {
value.map(|value| match value {
Value::String(str) => Value::String(str + &self.value),
_ => value,
})
})
}
}
#[Directive(location = "field")]
fn concat(value: String) -> impl CustomDirective {
ConcatDirective { value }
}
Register the directive when building the schema:
let schema = Schema::build(Query, EmptyMutation, EmptySubscription)
.directive(concat)
.finish();