Attribute Macro graphql_scalar

#[graphql_scalar]

#[graphql_scalar] macro.is interchangeable with #[derive(GraphQLScalar)] macro, and is used for deriving a GraphQL scalar implementation.

/// Doc comments are used for the GraphQL type description.
#[graphql_scalar]
#[graphql(
    // Custom GraphQL name.
    name = "MyUserId",
    // Description can also specified in the attribute.
    // This will the doc comment, if one exists.
    description = "...",
    // Optional specification URL.
    specified_by_url = "https://tools.ietf.org/html/rfc4122",
    // Explicit generic scalar.
    scalar = S: juniper::ScalarValue,
    transparent,
)]
struct UserId(String);

Foreign types

Additionally, #[graphql_scalar] can be used directly on foreign types via type alias, without using the newtype pattern.

NOTE: To satisfy orphan rules you should provide local ScalarValue implementation.

use juniper::{graphql_scalar, InputValue, ScalarValue, Value};

#[graphql_scalar]
#[graphql(
    with = date_scalar,
    parse_token(String),
    scalar = CustomScalarValue,
)]
//           ^^^^^^^^^^^^^^^^^ local `ScalarValue` implementation
type Date = date::Date;
//          ^^^^^^^^^^ type from another crate

mod date_scalar {
    use super::*;

    pub(super) fn to_output(v: &Date) -> Value<CustomScalarValue> {
        Value::scalar(v.to_string())
    }

    pub(super) fn from_input(v: &InputValue<CustomScalarValue>) -> Result<Date, String> {
      v.as_string_value()
          .ok_or_else(|| format!("Expected `String`, found: {v}"))
          .and_then(|s| s.parse().map_err(|e| format!("Failed to parse `Date`: {e}")))
    }
}