Deserialize JSON not working with JSON.NET

Question

I have a problem with the following JSON when deserializing using JSON.NET.

{
    "?xml": {
        "@version": "1.0",
        "@encoding": "utf-8"
    },
    "Persons": {
        "Person": [{
            "@Id": "1",
            "@Name": "John",
            "@Surname": "Smith"         
        },
        {
            "@Id": "2",
            "@Name": "John",
            "@Surname": "Smith",
            "Skills": {
                "Skill": [{
                    "@Id": "1",
                    "@Name": "Developer"                    
                },
                {
                    "@Id": "2",
                    "@Name": "Tester"
                }]
            }
        }]
    }
}

I'm using the following classes:

public class RootObject
{
    public Xml xml { get; set; }
    public Persons Persons { get; set; }
}

public class Xml
{
    public string version { get; set; }
    public string encoding { get; set; }
}

public class Persons
{
    public List<Person> Person { get; set; }
}
public class Skill
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Skills
{
    public List<Skill> Skill { get; set; }
}

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Surname { get; set; }
    public Skills Skills { get; set; }
}

When i try to deserialize

RootObject persons = JsonConvert.DeserializeObject<RootObject>(json);

i got the following error:

Cannot deserialize the current JSON object (e.g. {"name":"value"}) into type 'System.Collections.Generic.List`1[Project.Models.Persons.Skill]' because the type requires a JSON array (e.g. [1,2,3]) to deserialize correctly. To fix this error either change the JSON to a JSON array (e.g. [1,2,3]) or change the deserialized type so that it is a normal .NET type (e.g. not a primitive type like integer, not a collection type like an array or List) that can be deserialized from a JSON object. JsonObjectAttribute can also be added to the type to force it to deserialize from a JSON object.

I suppose the problem is in the notation:

"Skills": {
            "Skill": [{

What am I missing, is there an easy solution to this problem?

UPDATE:

So finally the problem was that it was sometimes a JSON array

"Skills": {
                "Skill": [{

and sometimes a JSON object

"Skills": {
                "Skill": {

But when pasting/checking my code into validators it would always be formatted as a JSON array so i've inspected it using watch window to see the raw json string.

From there it was easy to mark the property with a JsonConverter attribute

public class Skills
    {
        [JsonConverter(typeof(MyConverter))]
        public List<Skill> Skill { get; set; }
    }

and write the converter:

public class MyConverter : JsonConverter
    {
        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            if (reader.TokenType == JsonToken.StartArray)
            {
                return serializer.Deserialize<List<Skill>>(reader);
            }
            else
            {
                Skill skill = serializer.Deserialize<Skill>(reader);
                return new List<Skill>(new[] { skill});
            }
        }      

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            writer.WriteValue(value);
        }
    }

Hope it helps somebody.

Reading your json in from a file, and deserializing with your code, it all works fine for me. — Pondidum
Fantastic answer. You should mark it as the accepted answer. Worked perfect for me. Only change I made was to make the converter generic instead of hard coded for any one type (Skill in your example) — enablor
@GregLoehr Glad it helped. I've implemented an generic converter too. This is just an example for the given problem. — Matija Grcic
If your answering your own question, the answer should be an actual answer below — Liam

Davin Tryon Davin Tryon · Accepted Answer · 2013-01-07T15:02:24

I think, with your current JSON, you are describing that Skill contains a collection, not Skills. Try this JSON instead:

        "Skills": [
            {
                "@Id": "1",
                "@Name": "Developer"
            },
            {
                "@Id": "2",
                "@Name": "Tester"
            }
        ]

The same thing applies to how you are defining the Persons collection.

EDIT:

This test passes for me:

    [TestFixture]
    public class JSONTester
    {
        [Test]
        public void Json_deserialize()
        {
            var json = @"{
    ""?xml"": {
        ""@version"": ""1.0"",
        ""@encoding"": ""utf-8""
    },
    ""Persons"": {
        ""Person"": [{
            ""@Id"": ""1"",
            ""@Name"": ""John"",
            ""@Surname"": ""Smith""         
        },
        {
            ""@Id"": ""2"",
            ""@Name"": ""John"",
            ""@Surname"": ""Smith"",
            ""Skills"": {
                ""Skill"": [{
                    ""@Id"": ""1"",
                    ""@Name"": ""Developer""                    
                },
                {
                    ""@Id"": ""2"",
                    ""@Name"": ""Tester""
                }]
            }
        }]
    }
}";

            var persons = JsonConvert.DeserializeObject<RootObject>(json);

            Assert.AreEqual(persons.Persons.Person[1].Skills.Skill.Count, 2);

        }

        public class RootObject
        {
            public Xml xml { get; set; }
            public Persons Persons { get; set; }
        }

        public class Xml
        {
            public string version { get; set; }
            public string encoding { get; set; }
        }

        public class Persons
        {
            public List<Person> Person { get; set; }
        }
        public class Skill
        {
            public int Id { get; set; }
            public string Name { get; set; }
        }

        public class Skills
        {
            public List<Skill> Skill { get; set; }
        }

        public class Person
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public string Surname { get; set; }
            public Skills Skills { get; set; }
        }
    }

Deserialize JSON not working with JSON.NET

1 Answers