How to deserialize response with dynamic field name? - rust

Question

Trying to Deserialize the response from a rust get request. The following request seems to work fine. However, I was wondering if there is a good way to model the TradeResult. Right now it has XXBTZUSD hard coded. I want this to be any type of pair. Tried using a HashMap<String, TradeResultTypes> type on the Trades result; was hoping this would allow both the last property and the pair being retrieved, but can't seem to get this to work unless the pair is hard coded as it is below.
extern crate serde;
#[macro_use]
extern crate serde_derive;
use std::collections::HashMap;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let resp: Trades = reqwest::blocking::get("https://api.kraken.com/0/public/Trades?pair=XBTUSD")?.json()?;
println!("{:?}", resp);
Ok(())
}
#[derive(Debug, Deserialize)]
struct Trades {
result: TradeResult,
error: Vec<u32>,
}
// #[derive(Debug, Deserialize)]
// struct Trades {
// result: HashMap<String, TradeResultTypes>,
// error: Vec<u32>,
// }
#[derive(Debug, Deserialize)]
struct TradeResult {
last: String,
XXBTZUSD: TradeData,
}
// (price, volume, time, side, orderType, misc)`
type TradeData = Vec<(String, String, f64, String, String, String)>;
#[derive(Debug, Deserialize)]
enum TradeResultTypes {
String,
TradeData,
}

Answer 1

You can use the untagged attribute to deserialize either a String or a TradeData:
#[derive(Debug, Deserialize)]
struct Trades {
result: HashMap<String, TradeResultTypes>,
error: Vec<u32>,
}
// (price, volume, time, side, orderType, misc)`
type TradeData = Vec<(String, String, f64, String, String, String)>;
#[derive(Debug, Deserialize)]
#[serde(untagged)]
enum TradeResultTypes {
String (String),
TradeData (TradeData),
}
This way, serde will first attempt to deserialize a String. If it works, it will return a TradeResultTypes::String. If it doesn't work, it will try to deserialize an array of tuples. If that works it will return a TradeResultTypes::TradeData, otherwise it will return an error.
Note that you need to tell Rust the type of value that is to be stored in each variant of the enum. In other words when I write String (String) inside the enum, the first String is only a label (which serde will ignore due to the untagged attribute) and the second String is the type of data that it's supposed to contain. It would work as well with:
#[derive(Debug, Deserialize)]
#[serde(untagged)]
enum TradeResultTypes {
Last (String),
Quotations (TradeData),
}