Easy(er) way to deserialize a HashMap<&str, serde_json::Value>

[svanharmelen]

I know there is a serde_json::Map which has String keys, but I would really like to use something like this:

let mut data: HashMap<&str, serde_json::Value> = serde_json::from_str(content).unwrap();
// do custom stuff
let v: MyStruct = serde_json::from_value(serde_json::to_value(data).unwrap()).unwrap();

This works, but it would be nice if there is a way to do this without the additional to_value. Is that possible? Thanks!

[dtolnay]

The IntoDeserializer trait and the implementations of it in serde::de::value provide a way to deserialize directly from a map without the to_value conversion or allocations.

use serde::de::value::MapDeserializer;
use serde::Deserialize;
use serde_json::Value;
use std::collections::HashMap;

#[derive(Deserialize, Debug)]
struct MyStruct {
    a: usize,
    b: usize,
}

fn main() {
    let content = "{\"a\":1}";
    let mut data: HashMap<&str, Value> = serde_json::from_str(content).unwrap();
    data.insert("b", Value::from(2));
    let v = MyStruct::deserialize(MapDeserializer::new(data.into_iter())).unwrap();
    println!("{:#?}", v);
}

[svanharmelen]

Super nice @dtolnay! Exactly the kind of solution I was hoping for 👍 Thanks!

[svanharmelen]

Hmm... I actually have the same issue/question for doing this the other way around.

So serialize a struct into a HashMap. Again I can do this in two stages (first using to_value and then using from_value to get a HashMap, but I guess/hope there is be a better way to achieve this?

Additionally, if I do take the above two-step approach, I cannot use a HashMap<&str, Value> without getting lifetime errors which requires me to use a HashMap<String, Value> instead.

If doing this more elegant (in one go) isn;t possible, that it would be great to know how I can keep using &str keys instead of String keys.

Thanks!

[svanharmelen]

Hmm...Maybe a better solution for my problem/challenge is something along the lines of #1470

Asked an addition question there about that approach so if that works out this one can be closed...

[svanharmelen]

Guess I'll close this issue as I don't expect any updates anymore...

[norbertkeri]

@dtolnay I can't seem to get your example to work with serde_yaml (but it works fine with json). Am I doing something wrong, or is this just a feature that is not yet implemented?

error[E0277]: the trait bound `serde_yaml::value::Value: _::_serde::de::IntoDeserializer<'_, _>` is not satisfied
  --> src/main.rs:16:35
   |
16 |     let v = MyStruct::deserialize(MapDeserializer::new(data.into_iter())).unwrap();
   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `_::_serde::de::IntoDeserializer<'_, _>` is not implemented for `serde_yaml::value::Value`
   |
   = note: required because of the requirements on the impl of `_::_serde::Deserializer<'_>` for `_::_serde::de::value::MapDeserializer<'_, std::collections::hash_map::IntoIter<&str, serde_yaml::value::Value>, _>`
   = note: required by `_::_serde::Deserialize::deserialize`

error: aborting due to previous error

[dtolnay]

@norbertkeri serde_yaml does not implement this but I filed dtolnay/serde-yaml#169 to follow up.

[norbertkeri]

Thanks!