Deserializing a JSON with nested dynamic property names

Question

I'm trying to deserialize a pretty ugly JSON provided by an external REST API and am wondering about the "proper" way to do that (I'm using System.Text.Json in .net 6). Details follow:

I have a model for the data:

class DeviceData{
    //lots of properties
}

which works fine (i.e I can just JsonSerializer.Deserialize<DeviceData> the response) when making an API query for a single instance, since it returns a nice JSON one would expect:

{
    "property1_name": value,
    "property2_name": value,
    ...
}

The problem begins when I use the batch query provided by the API, since the response to api_url/batch?=device1,device2,... looks as if someone failed to make an array (the device1s are alphanumeric strings pulled form a database) is:

{
"names":[
   "device1",
   "device2",
   ...
   ],
"device1":{
   "stuff_i_dont_need": value,
   "device1": {
       "property1_name": value,
       "property2_name": value,
        ...
    }
 }
 "device2":{
     ...
 }
 ...
}

The double nesting of dynamic property names means I can't just deserialize the second response as a dictionary of <string, myclass> pairs. I managed to hack something together using JsonDocument but it's extremly ugly and it feels like there should be a nice short way to do that with just JsonSerializer and maybe some reader overrides.

if you want to get a real help, you have to post a real json — Serge, Mar 03 '22 at 18:01

score 0 · Accepted Answer · answered Mar 04 '22 at 06:12

Using Deserialize subsections of a JSON payload from How to use a JSON document, Utf8JsonReader, and Utf8JsonWriter in System.Text.Json as template you could do something like this:

JsonNode root = JsonNode.Parse(json)!;

Dictionary<string, X> devices = new();
foreach(string name in root["names"]!.AsArray()) {
    var o = root[name][name].AsObject();
    using var stream = new MemoryStream();
    using var writer = new Utf8JsonWriter(stream);
    o.WriteTo(writer);
    writer.Flush();
    X? x = JsonSerializer.Deserialize<X>(stream.ToArray());

    var innerJson = root[name][name].ToJsonString();
    devices[name] = x;
}

foreach(var d in devices) Console.WriteLine($"{d.Key}: {d.Value}");

This prints

device1: X { property1_name = 12, property2_name = 13 }
device2: X { property1_name = 22, property2_name = 23 }

I'm not sure if this is faster/better than calling ToJsonString():

JsonNode root = JsonNode.Parse(json)!;

Dictionary<string, X> devices = new();
foreach(string name in root["names"]!.AsArray()) {
    var innerJson = root[name][name].ToJsonString();
    devices[name] = JsonSerializer.Deserialize<X>(innerJson);
}

foreach(var d in devices) Console.WriteLine($"{d.Key}: {d.Value}")

If you're after fancy you could go full LINQ:

JsonNode root = JsonNode.Parse(json)!;

Dictionary<string, X> devices = root["names"]!.AsArray()
    .Select(name => (string)name)
    .ToDictionary(
        keySelector: name => name, 
        elementSelector: name => System.Text.Json.JsonSerializer.Deserialize<X>(root[name][name].ToJsonString()));

foreach(var d in devices) Console.WriteLine($"{d.Key}: {d.Value}");

Both print

Deserializing a JSON with nested dynamic property names

1 Answers1