Deserialize JSON when structure known but not the keys - json

Question

I am trying to deserialize some crypto exchange JSON. The structure of the JSON is predictable but the keys are not. Each time the server adds a new currency it becomes a new key. For example, it looks something like this:
{
"timestamp":"1562405",
"username":"1234",
"BTC":
{"available":"0.00","orders":"0.00000000"},
"BCH":
{"available":"0.0000000","orders":"0.00000000"},
..
..
"GUSD":
{"available":"0.00","orders":"0.00"}
}
I tried the usual approach of defining a struct to deserialize into but every time there is a new currency my program will have an error.
I thought I would just read it all into a Value and then just iterate over it manually to put it all into a struct.
let balance_data: Value = serde_json::from_str(&String::from_utf8_lossy(&body)).unwrap();
println!("balance_data: {:?}", balance__data);
for element in balance_data.iter() {
//push into a proper map...
}
But I can't:
no method named `iter` found for type `serde_json::Value`.
I thought I would put it into a Vec<Value> but this causes a panic:
thread 'main' panicked at 'called ``Result::unwrap()` on an `Err` value: Error("invalid type: map, expected a sequence", line: 1, column: 0)'`
I also experimented with reading it into a HashMap but couldn't quite seem to crack it.
It would be amazing if we could do something like:
let balance_data: RecvBalance = serde_json::from_str(&String::from_utf8_lossy(&body)).unwrap();
#[derive(Debug, Deserialize)]
struct RecvBalance {
timestamp: String,
username: String,
HashMap<String, RecvBalanceData>,
}
#[derive(Debug, Deserialize)]
struct RecvBalanceData {
available: String,
orders: String,
}
Has anyone dealt with this situation? I need a struct with the balance data in it that I can lookup later in my program.

Answer 1

The doc has a related example. You need to put the HashMap and use flatten attribute:
#[derive(Debug, Deserialize)]
struct RecvBalance {
timestamp: String,
username: String,
#[serde(flatten)]
moneys: HashMap<String, RecvBalanceData>,
}