"key must be a string" when deserializing a JSON string with Serde

Question

I'm building a React app utilizing Rust for complex computations. In this case I'm passing a JSON formatted string from the React app to Rust:

{
  {'clientid': 1, 'category': 'Category #1', 'subcategory': 'Subcategory #1', 'cost': 1000.00},
  {'clientid': 1, 'category': 'Category #1', 'subcategory': 'Subcategory #2', 'cost': 2000.00}
}

I'm trying to figure out how to deserialze string In Rust into an array of structs defined as:

#[derive(Serialize, Deserialize, Debug)]
struct ClientBudget {
    clientid: u32,
    category: String,
    subcategory: String,
    cost: f32,
}

I tried:

let deserialized: ClientBudget = serde_json::from_str(&some_json).unwrap();

But this causes a panic:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error("key must be a string"

How do I get Rust/serde to process this JSON string?

If the string you are passing is exactly like you have shown at the top of your question, the error is because it is not valid JSON (uses `'` instead of `"` and isn't using `[]` for the array). In the future, please include a [mcve] in your question that demonstrates the problem, and preferably a [Rust playground](https://play.rust-lang.org/) link. — Herohtar, Aug 19 '20 at 17:40
There are many online tools you can use to validate your JSON string. https://jsonlint.com/ is the first I found on a quick search. You can also use `JSON.parse()` in your browsers JSON console. — Shepmaster, Aug 19 '20 at 17:51
Please don't change your question after receiving an answer. You are encouraged to instead open a new question (looking for any duplicates before asking it). — Shepmaster, Aug 19 '20 at 19:48
See also [How to set input as raw string in Rust?](https://stackoverflow.com/q/37889091/155423) — Shepmaster, Aug 19 '20 at 19:48
apologies, I thought that was what I was supposed to do after reading the info on the closed status. Thanks for your help. — chasahodge, Aug 19 '20 at 19:51

score 0 · Answer 1 · edited Aug 19 '20 at 17:50

0

Your JSON is badly formatted. If you want a list, you must use [] not {}. You also need to deserialize a Vec of objects:

use serde::{Deserialize, Serialize}; // 1.0.114

#[derive(Serialize, Deserialize, Debug)]
struct ClientBudget {
    clientid: u32,
    category: String,
    subcategory: String,
    cost: f32,
}

fn main() {
    let data = r#"
[
    {"clientid": 1, "category": "Category #1", "subcategory": "Subcategory #1", "cost": 1000.00},
    {"clientid": 1, "category": "Category #1", "subcategory": "Subcategory #2", "cost": 2000.00}
]
    "#;
    let deserialized: Vec<ClientBudget> = serde_json::from_str(data).unwrap();

    println!("{:?}", deserialized);
}

Playground

edited Aug 19 '20 at 17:50

Shepmaster

388,571
95
1,107
1,366

answered Aug 19 '20 at 17:41

Netwave

40,134
6
50
93

1

Your example/solution shows a Rust Vec object. That’s not what is being passed to Rust from React. What I’m getting from React is the form shown in my example which is proper JSON. – chasahodge Aug 19 '20 at 17:48
*which is proper JSON* — [citation needed]. – Shepmaster Aug 19 '20 at 17:51
5

My apologies. I was incorrect. I have always used the format shown in my example for JSON formatted data. Upon examining my output from react and using an online JSON validator I see now that I am wrong. Don’t know when things changed or how I got away with that structure in the past, but I now see the error of my ways. Thanks and apologies. – chasahodge Aug 19 '20 at 18:10

"key must be a string" when deserializing a JSON string with Serde

1 Answers1