Deserialzation from JSON file with multiple objects in C#

Question

I have a JSON-file people.json containing multiple objects that I want to parse to a list People containing Person objects but with no luck. I get null from peopleLis and I suspect that I do something (probably a lot) wrong here. Can you guys help me out?

{
    "Andrew": {
        "weight": "75",
        "height": "181"
    },
    "Nathalie": {
        "weight": "68",
        "height": "182"
    },
    "Dave": {
        "weight": "83",
        "height": "192"
    }
}

This is the code I tried out:

        public class Person
        {
            public int weight { get; set; }
            public int height { get; set; }
        }

        public class People
        {
            public List<Person> people { get; set; }
        }

        static void Main(string[] args)
        {
            People peopleList = JsonConvert.DeserializeObject<People>(File.ReadAllText(@"C:\people.json"));
        }

As a clue to what the problem is, you can put your JSON into this page, and see the classes that are generated. — Robert Harvey
– Robert Harvey, Commented Mar 18, 2021 at 12:18
The json should start with [ and end with ] for this to be a list of objects. Currently you have {, }.. — Menahem
– Menahem, Commented Mar 18, 2021 at 12:20

Jon Skeet · Accepted Answer · 2021-03-18 12:17:08Z

Your JSON doesn't represent a list of people - it represents a single object with multiple properties, where each property value is a person.

You can deserialize this to a Dictionary<string, Person>:

string json = File.ReadAllText(@"C:\people.json");
var people = JsonConvert.DeserializeObject<Dictionary<string, Person>>(json);

You can create a list from that if you want (e.g. people.Values.ToList()) but you shouldn't depend on the ordering of that list being the same as in the JSON file - fundamentally, JSON object properties aren't intended to be order-sensitive. Given that the name of the person is presumably important, I'd stick with using the dictionary, where the key of each entry is the name.

(As a side-note, I'd recommend using idiomatic names for the properties, so Weight and Height, then using [JsonProperty] to specify the JSON names if you need to.)

Peder Wistedt · Accepted Answer · 2021-03-18 14:08:26Z

There are a few things not working out here:

As mentioned above the JSON does not represent a List structure, it's really 3 different objects named Andrew, Nathalie and Dave
The above class "People" also has to be represented in the JSON - right now it's not.
Maybe there is a need for another field called "Name" just like "height" and "weight"
For the classes to store the values (I suspect you need that:)you will need member variables and not only the properties function

I don't know if you can change the JSON or/and the code but here is a piece of code and a JSON that might work for you - I did not try it out but you I think you get the picture

public class Person
{
    private string _name;
    private int _weight;
    private int _height;


    public string Name { get => _name; set => _name = value; }
    public int Height { get => _height; set => _height = value; }

    public int Weight { get => _weight; set => _weight = value; }
}

public class PeopleList
{
    private List<Person> people;

    public List<Person> People { get => people; set => people = value; }
}

static void Main(string[] args)
{
    PeopleList peopleList = JsonConvert.DeserializeObject<People>(File.ReadAllText(@"C:\people.json"));
}

And this is the JSON

{
  "People": [
    {
      "Name": "Andrew",
      "Weight": "75",
      "Height": "181"
    },
    {
      "Name": "Nathalie",
      "Weight": "68",
      "Height": "182"
    },
    {
      "Name": "Dave",
      "Weight": "83",
      "Height": "192"
    }
  ]
}

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