Define a directive for query.
*[See also the Book](https://async-graphql.github.io/async-graphql/en/custom_directive.html).*
# Macro attributes
| name | Object name | string | Y |
| name_type | If `true`, the directive name will be specified from [`async_graphql::TypeName`](https://docs.rs/async-graphql/latest/async_graphql/trait.TypeName.html) trait | bool | Y |
| visible | If `false`, it will not be displayed in introspection. *[See also the Book](https://async-graphql.github.io/async-graphql/en/visibility.html).* | bool | Y |
| visible | Call the specified function. If the return value is `false`, it will not be displayed in introspection. | string | Y |
| repeatable | It means that the directive can be used multiple times in the same location. | bool | Y |
| rename_args | Rename all the arguments according to the given case convention. The possible values are "lowercase", "UPPERCASE", "PascalCase", "camelCase", "snake_case", "SCREAMING_SNAKE_CASE". | string | Y |
| locations | Specify the location where the directive is available, multiples are allowed. The possible values is "field", ... | string | N |
# Directive arguments
| name | Argument name | string | Y |
| desc | Argument description | string | Y |
| deprecation | Argument deprecation | bool | Y |
| deprecation | Argument deprecation reason | string | Y |
| default | Use `Default::default` for default value | none | Y |
| default | Argument default value | literal | Y |
| default_with | Expression to generate default value | code string | Y |
| validator | Input value validator *[See also the Book](https://async-graphql.github.io/async-graphql/en/input_value_validators.html)* | object | Y |
| visible | If `false`, it will not be displayed in introspection. *[See also the Book](https://async-graphql.github.io/async-graphql/en/visibility.html).* | bool | Y |
| visible | Call the specified function. If the return value is `false`, it will not be displayed in introspection. | string | Y |
| secret | Mark this field as a secret, it will not output the actual value in the log. | bool | Y |
# Examples
```rust
use async_graphql::*;
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 }
}
struct Query;
#[Object]
impl Query {
async fn value(&self) -> &'static str {
"abc"
}
}
# tokio::runtime::Runtime::new().unwrap().block_on(async move {
let schema = Schema::build(Query, EmptyMutation, EmptySubscription)
.directive(concat)
.finish();
let res = schema.execute(r#"{ value @concat(value: "def") }"#).await.into_result().unwrap().data;
assert_eq!(res, value!({
"value": "abcdef",
}));
# });
```