Deserialize json object with dynamic items in C#

Question

I've got the following json document:

{
  "name": "bert",
  "Bikes": {
    "Bike1": {
      "value": 1000,
      "type": "Trek"
    },
    "Bike2": {
      "value": 2000,
      "type": "Canyon"
    }
  }
}

With potentially other bikes like Bike3...BikeN. I want to deserialize to C# objects. Problem is that in the deserialization step the bikes data is completely lost, resulting in a null Bikes collection.

Code to reproduce:

[Test]
public void FirstCityJsonParsingTest()
{
    var file = @"./testdata/test.json";
    var json = File.ReadAllText(file);

    var res = JsonConvert.DeserializeObject<Person>(json);
    Assert.IsTrue(res.Name == "bert");
    // next line is failing, because res.Bikes is null...
    Assert.IsTrue(res.Bikes.Count == 2);
}

public class Bike
{
    public string Id { get; set; }
    public int Value { get; set; }
    public string Type { get; set; }
}

public class Person
{
    public string Name { get; set; }
    public List<Bike> Bikes { get; set; }
}

To fix this problem a change in the used model is necessary. But what change is needed here to fill the bikes data correctly?

Note: Changing the input document is not an option (as it's a spec)

What do you mean by "it's failing"? What's the count? Did the Person object not get a Bikes property populated? Please be explicit in describing what's happening. — mason
– mason, Commented Jun 11, 2020 at 13:42
Bikes isn't an array, look at Dictionary<string, Bike> structure — Pavel Anikhouski
– Pavel Anikhouski, Commented Jun 11, 2020 at 13:43
try this ` public class Bike1 { public int value { get; set; } public string type { get; set; } } public class Bike2 { public int value { get; set; } public string type { get; set; } } public class Bikes { public Bike1 Bike1 { get; set; } public Bike2 Bike2 { get; set; } } public class Example { public string name { get; set; } public Bikes Bikes { get; set; } }` @bertt — Vivek Nuna
– Vivek Nuna, Commented Jun 11, 2020 at 13:46
Can you change the JSON document to have "Bikes" as an array ([ ]) instead of object ({ })? You then also have to move the Id ("Bike1") into the bike object as "id" property — Hans Keﬆing
– Hans Keﬆing, Commented Jun 15, 2020 at 8:41
@HansKeﬆing changing the input json is not an option in this case (because spec). — bertt
– bertt, Commented Jun 15, 2020 at 21:46

Guru Stron · Accepted Answer · 2022-12-20 14:46:35Z

7

Your code structure is not reflecting your json. Common approach to deserializing json with dynamic property names is to use Dictionary<string, ...> (supported both by Json.NET and System.Text.Json). Try the following:

public class Bike
{
    public int Value { get; set; }
    public string Type { get; set; }
}

public class Person
{
    public string Id { get; set; }
    public string Name { get; set; }
    public Dictionary<string, Bike> Bikes { get; set; }
}

Person.Bikes should be changed to Dictionary<string, Bike> (also Bike.Id property is not needed) cause Bikes json element is not an array but object.

edited Dec 20, 2022 at 14:46

answered Jun 11, 2020 at 13:44

Guru Stron

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