Json Deserialize Error, Problem C# .Net Core

Question

I have the following problem trying to deserialize JSON that I read from a file. I always get that it can't be deserialized by object type. What is causing this?

MyModel.cs

public class MyModel
{
    public List<toppings> Lista { get; set; }
}
public class toppings
{
    public string description { get; set; }
}

Program.cs

static void Main(string[] args)
{
    try
    {
        string json = File.ReadAllText(@"C:\Users\Ricciardo\Documents\Net Core Practice\Pizza\PizzaRead\pizzas.json").ToString();

        MyModel objetos = JsonSerializer.Deserialize<MyModel>(json);

        foreach (var ingrediente in objetos.Lista)
        {
            Console.WriteLine(ingrediente.description.ToString());
        }
    }

    catch (Exception ex)
    {
        Console.Write(ex.Message.ToString());
        throw ex;
    }
    Console.ReadKey();
}

JSON File

[
  {
    "toppings": [
      "pepperoni"
    ]
  },
  {
    "toppings": [
      "feta cheese"
    ]
  },
  {
    "toppings": [
      "pepperoni"
    ]
  },
  {
    "toppings": [
      "bacon"
    ]
  }
]

It appears that your JSON file contains an array of objects that have another array of toppings inside of each object. You may not be mapping the classes properly. — nulltron
– nulltron, Commented Jun 10, 2020 at 0:08
I posted an answer, it's a JSON > Class mapping issue. Hopefully, my answer gives you enough info to take the next steps =) — nulltron
– nulltron, Commented Jun 10, 2020 at 0:21

nulltron · Accepted Answer · 2020-06-10 00:19:24Z

2

It appears that your class structure doesn't match your JSON structure.

Your JSON is structured as such:

Array
- Object
  - Array (toppings)

Define your MyModel (or Pizza) class:

public class Pizza
{
    public List<string> Toppings {get; set;}
}

Then update your Program.cs Main method:

    static void Main(string[] args)
    {
        try
        {
            string json = File.ReadAllText(@"C:\Users\Ricciardo\Documents\Net Core Practice\Pizza\PizzaRead\pizzas.json").ToString();

            var objetos = JsonSerializer.Deserialize<List<Pizza>>(json);

            foreach (var pizza in objetos)
            {
                //Console.WriteLine(ingrediente.description.ToString());
                // TODO: Manipulate pizza objeto
            }
        }

        catch (Exception ex)
        {
            Console.Write(ex.Message.ToString());
            throw ex;
        }
        Console.ReadKey();
    }

You may have to tweak with the casing a little.

Also, a side note the way the JSON is structured poses some problems.

A structure similar to this may help you out more:

[
  {
    "Toppings": [
        {
          "name":"pepperoni"
          "description":"blah"
        },
    ]
  },
]

Then you could actually define a Topping class like so:

public class Topping 
{
    public string Name {get; set;}

    public string Description {get; set;}
}

And change up the Pizza class (MyModel):

public class Pizza 
{
    public List<Topping> Toppings {get; set;}
}

answered Jun 10, 2020 at 0:19

nulltron

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1 Comment

Daniel Lazarte Over a year ago

Hi, thanks for your response. I cannot change the json data source. This is how it is structured. Try what you sent me but it doesn't work :(

Pavel Anikhouski · Accepted Answer · 2020-07-17 14:28:44Z

0

Your JSON is an array, where every item has toppings array of strings. So, the proper model should be something like that (decorated with JsonPropertyName attribute)

using System.Text.Json;
using System.Text.Json.Serialization;

//rest of code

public class MyModel
{
    [JsonPropertyName("toppings")]
    public List<string> Toppings { get; set; }
}

And deserialization to List<MyModel>

var result = JsonSerializer.Deserialize<List<MyModel>>(jsonString);
foreach (var item in result) 
    Console.WriteLine(string.Join(", ", item.Toppings));

It gives you a list with 4 items, where every item is a list with single string inside

edited Jul 17, 2020 at 14:28

answered Jun 10, 2020 at 7:11

Pavel Anikhouski

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2 Comments

Daniel Lazarte Over a year ago

Esta es la solución, funciona a la perfección. Te lo agradezco muchisimo. un abrazo

Pavel Anikhouski Over a year ago

@DanielLazarte Sorry, I don't know Spanish:) But welcome, glad to help

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