How to build json arrays or objects dynamically with serde_json?

Question

I need to build a json object at runtime. For now, just a simple {"key": "stringvalue"} object. But each key/val pair must be added in a loop.

This seems really simple/basic, but I didn't find any good examples or docs on it. I did finally manage to make something work, but it seems too convoluted to be the right way.

Can anyone post a working example?

please explain more, I think you could just create a hashmap or struct and serialize it. You are doing it the wrong way. — Stargateur
– Stargateur, Commented Nov 26, 2019 at 17:23

Mac O'Brien · Accepted Answer · 2019-11-26 09:41:08Z

19

You can do this with serde_json::Value:

use serde_json::{Map, Value};

let mut map = Map::new();

// assuming keys_vals is a Vec<(String, String)>
for (key, val) in keys_vals.into_iter() {
    map.insert(key, Value::String(val));
}

let obj = Value::Object(map);

If you need to have the object constructed and still update the map:

let mut obj = Value::Object(map);

if let Value::Object(ref mut map) = obj {
    map.insert(key, val);
}

answered Nov 26, 2019 at 9:41

Mac O'Brien

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