Deserialize struct from query that isn't present in schema

[djkato]

Hello, having the following query:

subscription transactionInitializeSession {
  event {
    ... on TransactionInitializeSession {
      data
      sourceObject {
        __typename
        ... on Checkout {
          ...CheckoutDetails
        }
        ... on Order {
          ...OrderDetails
        }
      }
    }
  }
}

And the following rust structs:

#[derive(cynic::QueryFragment, Debug)]
#[cynic(graphql_type = "TransactionInitializeSession")]
pub struct TransactionInitializeSession2 {
    pub data: Option<Json>,
    pub source_object: OrderOrCheckout,
}
//...
#[derive(cynic::Scalar, Debug, Clone)]
#[cynic(graphql_type = "JSON")]
pub struct Json(pub String);

I get error Response creation failed: invalid type: map, expected a string at line 1 column 9
For data:

"{\"data\": {\"payment_method\": \"transfer\"}, \"sourceObject\": {\"__typename\": \"Checkout\", \"id\": \"Q2hlY2tvdXQ6YWQ5ZDI5NDYtODVlZi00ZDQzLTllOWUtYTY0Njk4M2I2NjVi\", \"
isShippingRequired\": true, \"deliveryMethod\": {\"__typename\": \"Warehouse\", \"name\": \"Lu\\u010dat\\u00edn\", \"id\": \"V2FyZWhvdXNlOjBiMTVjYjUyLTY0YWItNDA2OC1hMDgyLWFjNDAyZjcyZWM4OA==\"}}, \"transaction\": {\"id\": \"VHJhbnNhY3Rpb25JdGVtOjk1Mzk0Yjk
xLTY5NjItNGM4Zi1iNzJmLTg5YWI5NGMyMTJiOA==\", \"actions\": [], \"externalUrl\": \"\", \"message\": \"\", \"authorizedAmount\": {\"currency\": \"EUR\", \"amount\": 0.0}, \"authorizePendingAmount\": {\"currency\": \"EUR\", \"amount\": 0.0}, \"canceledAmount
\": {\"currency\": \"EUR\", \"amount\": 0.0}, \"cancelPendingAmount\": {\"currency\": \"EUR\", \"amount\": 0.0}, \"chargedAmount\": {\"currency\": \"EUR\", \"amount\": 0.0}, \"chargePendingAmount\": {\"currency\": \"EUR\", \"amount\": 0.0}, \"refundedAmo
unt\": {\"currency\": \"EUR\", \"amount\": 0.0}}, \"action\": {\"amount\": 1.47, \"currency\": \"EUR\", \"actionType\": \"CHARGE\"}}"

I assume this is because my data is

{\"data\": {\"payment_method\": \"transfer\"},

and not an actual double escaped stringify like:

{"data":"{\\"payment_method\\":\\"transfer\\"}"},

Thus I would need to substitute the Json(pub String) with

#[derive(Serialize, Deserialize, Clone, Copy, Debug)]
pub struct ChosenPaymentMethodData {
    pub payment_method: PaymentMethodType,
}

but then using it like:

#[derive(cynic::QueryFragment, Debug)]
#[cynic(graphql_type = "TransactionInitializeSession")]
pub struct TransactionInitializeSession2 {
    pub data: Option<ChosenPaymentMethodData>,
    pub source_object: OrderOrCheckout,
}

gives error

rustc: the trait bound `queries::event_transactions::ChosenPaymentMethodData: cynic::schema::IsScalar<queries::event_transactions::schema::JSON>` is not satisfied
the following other types implement trait `cynic::schema::IsScalar<SchemaType>`:
  <bool as cynic::schema::IsScalar<bool>>
  <i32 as cynic::schema::IsScalar<i32>>
  <f64 as cynic::schema::IsScalar<f64>>
  <std::boxed::Box<U> as cynic::schema::IsScalar<std::boxed::Box<T>>>
  <std::borrow::Cow<'_, U> as cynic::schema::IsScalar<T>>
  <cynic::Id as cynic::schema::IsScalar<cynic::Id>>
  <std::vec::Vec<U> as cynic::schema::IsScalar<std::vec::Vec<T>>>
  <std::string::String as cynic::schema::IsScalar<std::string::String>>
and 7 others
required for `std::option::Option<queries::event_transactions::ChosenPaymentMethodData>` to implement `cynic::schema::IsScalar<std::option::Option<queries::event_transactions::schema::JSON>>` [E0277]

I can't define it as scalar cause that's not what it is, and I can't define it as a fragment cause then it complains that it's not in the schema as such.

How can I solve this?

[obmarg]

So I'm guessing in the GraphQL schema this is defined as JSON, which is a scalar that represents arbitrary some arbitrary JSON object?

You've got a few options for handling this:

1. Define ChosenPaymentMethodData as you've done above, and then put cynic::impl_scalar!(ChosenPaymentMethodData, schema::JSON) afterwards, and it should work. You can do cynic::impl_scalar on any type that implements Serialize & Deserialize, and it'll become acceptable in positions expecting the given scalar. It's often better than deriving Scalar for that reason. Although it's worth noting that this will let you use ChosenPaymentMethodData on any JSON field, not just this one. So be careful with that.
2. You can use serde_json::Value. Either directly after doing impl_scalar!(serde_json::Value, schema::JSON), or by deriving it:

#[derive(cynic::Scalar, Debug, Clone)]
#[cynic(graphql_type = "JSON")]
pub struct Json(pub serde_json::Value);

This would generally be the best option if the type of data isn't always compatible with the ChosenPaymentMethodData struct that you've defined.