How to get property value from .net dynamic array object

Question

I've got a json file containing

{
  "Accounts": null,
  "AccountTypes": null,
  "Actions": null,
  "Photos": [
    {
      "Instance": "...",
      "Key": "..."
    },
    ....
  ]
}

Now I want to get all the Instance properties from the Photo objects. I've got the following code:

var photos = new List<Photo>();

string json = File.ReadAllText(file);
dynamic jsonObj = Newtonsoft.Json.JsonConvert.DeserializeObject(json, typeof(object));
var jsonPhotos = jsonObj.Photos as IEnumerable<dynamic>;
var instances = jsonPhotos.Select(x => x.Instance);

foreach (var instance in instances)
    photos.Add(new Photo
    {
        Document = Convert.FromBase64String(instance)
    });

However, jsonPhotos.Select(x => x.Instance); isn't returning anything...

I am able to get things working by using

var instances = new List<string>();

foreach (var photo in jsonPhotos)
    instances.Add(photo.Instance.Value);

But can I solve this in a LINQ way?

your json format is wrong. there is a comma missing after "Instance": "...", if you fix it the problem goes away. — Bizhan
– Bizhan, Commented Jul 10, 2020 at 9:52
Sorry, the typo only exists in my question here. In my real code there was never a typo — kristofvdj88
– kristofvdj88, Commented Jul 10, 2020 at 9:57
but jsonPhotos.Select(x => x.Instance); does return something — Bizhan
– Bizhan, Commented Jul 10, 2020 at 10:45

Pavel Anikhouski · Accepted Answer · 2020-07-10 10:57:05Z

2

Why just don't use Json.Linq for that? Parse JSON to JObject instance, then map every token from Photos array to Photo instance (I've omitted Convert.FromBase64String because OP sample doesn't have a valid base64 data, but converting Instance value can be easily added)

var json = JObject.Parse(jsonString);

var photos = json["Photos"]
    .Select(token => new Photo
    {
        Document = token["Instance"]?.Value<string>()
    })
    .ToList();

edited Jul 10, 2020 at 10:57

answered Jul 10, 2020 at 10:07

Pavel Anikhouski

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Comments

sunside · Accepted Answer · 2020-07-10 10:37:45Z

0

The .Select(x => x.Instance) indeed returns ... on .NET Core 3.1. Can you verify that the contents of the json variable are actually what you expect?

Specifically

jsonPhotos.Select(x => x.Instance);

works as expected, while

jsonPhotos.Select(x => x.SomeNonExistingProperty);

enumerates nothing / empty values.

For example, this code prints Instance A, then Instance B, then nothing twice:

var json = @"
{
    ""Photos"": [
    {
        ""Instance"": ""Instance A"",
        ""Key"": ""...""
    },
    {
        ""Instance"": ""Instance B"",
        ""Key"": ""...""
    }]
}";

var jsonObj = JsonConvert.DeserializeObject<dynamic>(json);
var jsonPhotos = jsonObj.Photos as IEnumerable<dynamic>;

var instances = jsonPhotos.Select(x => x.Instance);
foreach (var instance in instances)
{
    Console.WriteLine(instance);
}

// In contrast, this one will print empty lines.
instances = jsonPhotos.Select(x => x.SomeNonExistingProperty);
foreach (string instance in instances)
{
    Console.WriteLine(instance);
}

I took the liberty to change the deserialization to dynamic directly, but it also works with the original code from the question.

edited Jul 10, 2020 at 10:37

answered Jul 10, 2020 at 9:53

sunside

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2 Comments

sunside Over a year ago

The typo is not the issue, since that one results in a JsonReaderException.

kristofvdj88 Over a year ago

Sorry, the typo only exists in my question. In my real code there is no typo... I've edit my question and fixed the typo

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