Cant serialize when using enum as key in Hashmap

Question

use serde::{Deserialize, Serialize};

#[derive(Debug, PartialEq, Serialize, Deserialize)]
pub struct Demo {
    #[serde(with = "serde_with::json::nested")]
    pub something: HashMap<Option<Resource>, bool>,
}

#[derive(Debug, PartialEq, Serialize, Deserialize, Eq, Hash)]
pub enum Resource {
    #[serde(rename = "cpu")]
    Cpu,
    #[serde(rename = "memory")]
    Memory,
}

I am using an Enum property "Resource" as my hashmap key. Now, I want to send my data to an HTTP endpoint, so I want to serialize the data. This is how I did it :

let mut something = HashMap::new();
something.insert(Some(Cpu), true);

let data = Demo{
    something: something,
};


let serialized = serde_json::to_string(&data).unwrap();
println!("serialized {}", serialized);

But, the to_string is failing saying ==> Error("key must be a string", line: 0, column: 0)

can I map my enum values to be string at the time of serialization ? How to solve this ?

Answer 1

You can use different annotations from serde_with to make your example work. The problem how you used serde_with::json::nested is that it converts the whole HashMap into a String, which fails, because the keys do not serialize as strings. If you apply the attribute only to the key part, it works.

#[serde_with::serde_as]
#[derive(Debug, PartialEq, Serialize, Deserialize)]
pub struct Demo {
    #[serde_as(as = "HashMap<serde_with::json::JsonString, _>")]
    pub something: HashMap<Option<Resource>, bool>,
}