Is it possible to make the response of a query generic?

[cowlicks]

I would like to be able to define some query structs, and let the end user provide the structs for the response. My first attempt didn't work, and I got weird errors. Is there a way to do this?

Here the generic T parameter was previously ScanLogsConnection

#[derive(cynic::QueryVariables, Debug)]
pub struct LastTagAtScannerVariables {
    pub scanner_id: super::scalars::Uuid,
    pub tagged_type: String,
}

#[derive(cynic::QueryFragment, Debug)]
#[cynic(graphql_type = "Query", variables = "LastTagAtScannerVariables")]
pub struct LastTagAtScanner<T> {
    #[arguments(orderBy: "_CREATED_AT_DESC", condition: { hasTaggedType: $tagged_type, scannerId: $scanner_id }, first: 1)]
    pub scan_logs: Option<T>,
}

#[derive(cynic::QueryFragment, Debug)]
pub struct ScanLogsConnection {
    pub edges: Vec<ScanLogsEdge>,
}

But I could not figure out how to actually tell LastTagAtScanner about what I want T to be when I build it.

use foo::cynic_queries::{
    last_tag_at_scanner::{
        LastTagAtScanner, LastTagAtScannerVariables, ScanLogsConnection,
    },
    scalars::Uuid,
    QueryBuilder,
};
let mut client = Client::try_from_env()?;
let operation = LastTagAtScanner::build(LastTagAtScannerVariables {
    scanner_id: Uuid("0000d754-0000-0000-0000-0000646417b5".to_string()),
    tagged_type: "Thing".to_string(),
});
let x = client.cynic_query(operation).await?;

This is the error I get. The missing generic argument ... <T><T> is strange.

error[E0412]: cannot find type `T` in this scope
   --> src/cynic_queries.rs:844:31
    |
844 |         pub scan_logs: Option<T>,
    |                               ^ not found in this scope

error[E0107]: missing generics for struct `LastTagAtScanner`
   --> src/cynic_queries.rs:842:16
    |
842 |     pub struct LastTagAtScanner<T> {
    |                ^^^^^^^^^^^^^^^^ expected 1 generic argument
    |
note: struct defined here, with 1 generic parameter: `T`
   --> src/cynic_queries.rs:842:16
    |
842 |     pub struct LastTagAtScanner<T> {
    |                ^^^^^^^^^^^^^^^^ -
help: add missing generic argument
    |
842 |     pub struct LastTagAtScanner<T><T> {
    |                ~~~~~~~~~~~~~~~~~~~

Some errors have detailed explanations: E0107, E0412.

[obmarg]

Hi @cowlicks - I think this should be possible yeah.

Those errors are a bit odd - are you on v3 yet? Generic support was only added in v3, but those errors look kind of like what I'd expect from v2.

You'll also need to put some generic bounds in which you don't have there:

pub struct LastTagAtScanner<T> 
    where 
        T: cynic::QueryFragment<SchemaType = schema::ScanLogsConnection>,
        LastTagAtScannerVariablesFields: cynic::queries::VariableMatch<T::VariablesFields>,
{
   ...
}

But I could not figure out how to actually tell LastTagAtScanner about what I want T to be when I build it.

You'll want to use a turbofish to do that

LastTagAtScanner::<ScanLogsConnection>::build::(...)