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Determining object "type" during json deserialization

While trying to de-serialize a complex JSON object (JIRA issue) into an object containing a dictionary of type string-Field I've hit a bit of a bump.
While I can de-serialize various pre-determined object types (standard), I'm having a bit of a harder time with the custom fields, which could be of various types (they all begin with customfield_ followed by a set of numbers).
The custom fields can be floats, strings, booleans, objects and arrays of objects. The latter of these is causing me issues since I can't seem to determine what the object is before I de-serialize it.
I've searched for a way to perhaps "peek" at the data in the object before de-serializing as one of the fields contains information specific to it's type. This is all so I can determine the type of the object and tell Json.Net what to de-serialize it as.
I've considered parsing the JSON string before serialization to get the information, or maybe just when hitting this particular case, but maybe there is a better way?
Thanks in advance for any advice on this.

You can deserialize to an object with Json.Net. Here's a quick and dirty example:
using System;
using Newtonsoft.Json;
namespace Sandbox
{
class Program
{
private static void Main(string[] args)
{
var nestDto = new Dto
{
customfield_1 = 20,
customfield_2 = "Test2"
};
var dto = new Dto
{
customfield_1 = 10,
customfield_3 = new[] { nestDto },
customfield_2 = "Test"
};
var jsonString = JsonConvert.SerializeObject(dto);
Console.WriteLine(jsonString);
var fromJsonString = JsonConvert.DeserializeObject<Dto>(jsonString);
Console.WriteLine(fromJsonString.customfield_3[0].customfield_2); //Outputs Test2
Console.ReadKey();
}
}
class Dto
{
public int customfield_1 { get; set; }
public string customfield_2 { get; set; }
public Dto[] customfield_3 { get; set; }
}
}

Instead of peaking, you can deserialize as the same type as JSON.net uses for ExtensionData explicitly. For example:
if (reader.TokenType == JsonToken.StartArray)
{
var values = serializer.Deserialize<List<Dictionary<string, JToken>>>(reader);
objectContainer = ClassifyAndReturn(values);
}
private ObjectType ClassifyAndReturn(List<Dictionary<string, JToken>> values)
{
if (values.First().ContainsKey("self"))
{
string self = values.First()["self"].Value<string>();
if (self.Contains("customFieldOption"))
//... Then go into a series of if else cases to determine the object.
The representation of the objects are given as a Dictionary of string to JToken, which can then easily be checked and assigned manually or in some cases automatically deserialized (in the case one of the fields is another object).
Here is what an object constructor could look like:
internal myobject(Dictionary<string, JToken> source)
{
Self = source["self"].Value<string>();
Id = source["id"].Value<string>();
Value = source["value"].Value<string>();
}

Cannot deserialize the current JSON object (e.g. {"name":"value"}) into type 'System.Collections.Generic.List`1

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Facebook;
using Newtonsoft.Json;
namespace facebook
{
class Program
{
static void Main(string[] args)
{
var client = new FacebookClient(acc_ess);
dynamic result = client.Get("fql", new { q = "select target_id,target_type from connection where source_id = me()"});
string jsonstring = JsonConvert.SerializeObject(result);
//jsonstring {"data":[{"target_id":9503123,"target_type":"user"}]}
List<RootObject> datalist = JsonConvert.DeserializeObject<List<RootObject>>(jsonstring);
}
public class Datum
{
public Int64 target_id { get; set; }
public string target_type { get; set; }
}
public class RootObject
{
public List<Datum> data { get; set; }
}
}
}
Cannot deserialize the current JSON object (e.g. {"name":"value"})
into type
'System.Collections.Generic.List`1[facebook.Program+RootObject]'
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
I looked at other posts.
My json looks like this:
{"data":[{"target_id":9503123,"target_type":"user"}]}

To make it clear, in addition to #SLaks' answer, that meant you need to change this line :
List<RootObject> datalist = JsonConvert.DeserializeObject<List<RootObject>>(jsonstring);
to something like this :
RootObject datalist = JsonConvert.DeserializeObject<RootObject>(jsonstring);

As the error message is trying very hard to tell you, you can't deserialize a single object into a collection (List<>).
You want to deserialize into a single RootObject.

Can you try to change your json without data key like below?
[{"target_id":9503123,"target_type":"user"}]

That happened to me too, because I was trying to get an IEnumerable but the response had a single value. Please try to make sure it's a list of data in your response. The lines I used (for api url get) to solve the problem are like these:
HttpResponseMessage response = await client.GetAsync("api/yourUrl");
if (response.IsSuccessStatusCode)
{
IEnumerable<RootObject> rootObjects =
awaitresponse.Content.ReadAsAsync<IEnumerable<RootObject>>();
foreach (var rootObject in rootObjects)
{
Console.WriteLine(
"{0}\t${1}\t{2}",
rootObject.Data1, rootObject.Data2, rootObject.Data3);
}
Console.ReadLine();
}
Hope It helps.

The real problem is that you are using dynamic return type in the FacebookClient Get method. And although you use a method for serializing, the JSON converter cannot deserialize this Object after that.
Use insted of:
dynamic result = client.Get("fql", new { q = "select target_id,target_type from connection where source_id = me()"});
string jsonstring = JsonConvert.SerializeObject(result);
something like that:
string result = client.Get("fql", new { q = "select target_id,target_type from connection where source_id = me()"}).ToString();
Then you can use DeserializeObject method:
var datalist = JsonConvert.DeserializeObject<List<RootObject>>(result);
Hope this helps.

public partial class tree
{
public int id { get; set; }
public string name { get; set; }
public string sciencename { get; set; }
public int familyid { get; set; }
}
private async void PopulateDataGridView()
{
//For Single object response
tree treeobj = new tree();
treeobj = JsonConvert.DeserializeObject<tree>(Response);
//For list of object response
List<tree> treelistobj = new List<tree>();
treelistobj = JsonConvert.DeserializeObject<List<tree>>(Response);
//done
}

Serialize list of interface types with ServiceStack.Text

I'm looking at ways to introduce something other than BinaryFormatter serialization into my app to eventually work with Redis. ServiceStack JSON is what I would like to use, but can it do what I need with interfaces?
It can serialize (by inserting custom __type attribute)
public IAsset Content;
but not
public List<IAsset> Contents;
- the list comes up empty in serialized data. Is there any way to do this - serialize a list of interface types?
The app is big and old and the shape of objects it uses is probably not going to be allowed to change.
Thanks

Quoting from http://www.servicestack.net/docs/framework/release-notes
You probably don't have to do much :)
The JSON and JSV Text serializers now support serializing and
deserializing DTOs with Interface / Abstract or object types. Amongst
other things, this allows you to have an IInterface property which
when serialized will include its concrete type information in a __type
property field (similar to other JSON serializers) which when
serialized populates an instance of that concrete type (provided it
exists).
[...]
Note: This feature is automatically added to all
Abstract/Interface/Object types, i.e. you don't need to include any
[KnownType] attributes to take advantage of it.
By not much:
public interface IAsset
{
string Bling { get; set; }
}
public class AAsset : IAsset
{
public string Bling { get; set; }
public override string ToString()
{
return "A" + Bling;
}
}
public class BAsset : IAsset
{
public string Bling { get; set; }
public override string ToString()
{
return "B" + Bling;
}
}
public class AssetBag
{
[JsonProperty(TypeNameHandling = TypeNameHandling.None)]
public List<IAsset> Assets { get; set; }
}
class Program
{
static void Main(string[] args)
{
try
{
var bag = new AssetBag
{
Assets = new List<IAsset> {new AAsset {Bling = "Oho"}, new BAsset() {Bling = "Aha"}}
};
string json = JsonConvert.SerializeObject(bag, new JsonSerializerSettings()
{
TypeNameHandling = TypeNameHandling.Auto
});
var anotherBag = JsonConvert.DeserializeObject<AssetBag>(json, new JsonSerializerSettings()
{
TypeNameHandling = TypeNameHandling.Auto
});

Json.Net duplicates private list items

Currently I'm trying to utilize Json.Net serializer in my projects.
One of the problems that I've faced recentry is that deserialized object gets all of it's private list items duplicated.
It can be reproduced like this:
Create class with private field of List<> type, where List<> generic parameter is some other class
Add public property, that gets/sets private field
Create instance of that class, add 1 item to inner list, using property.
Serialize with new DefaultContractResolver that is setup to see private class data;
Deserialize
Code to reproduce the problem:
public class ClassParam
{
public int? ParamOne
{
get;
set;
}
}
public class ClassWithParams
{
private List<ClassParam> _privateFieid = new List<ClassParam>();
public List<ClassParam> PropertWithBackingField
{
get { return _privateFieid; }
set { _privateFieid = value; }
}
public void AddElementToPrivateField(ClassParam classParam)
{
_privateFieid.Add(classParam);
}
}
[Test]
public void Test()
{
var instance = new ClassWithParams();
var param1 = new ClassParam { ParamOne = 1 };
instance.PropertWithBackingField.Add(param1);
var contractResolver = new DefaultContractResolver();
contractResolver.DefaultMembersSearchFlags |= BindingFlags.NonPublic;
string serializedInstance = JsonConvert.SerializeObject(instance,
Formatting.Indented,
new JsonSerializerSettings()
{
ContractResolver = contractResolver
});
var deserializeInstance = JsonConvert.DeserializeObject(serializedInstance, typeof(ClassWithParams),
new JsonSerializerSettings()
{
ContractResolver = contractResolver
});
}
When I remove public property PropertWithBackingField from ClassWithParams it's all ok.
The problem is gone as well when I don't use custom setup for ContractResolver. But I do need to serialize private data of my classes as soon as not all of it is exposed via public properties.
What's wrong with my code? Are there any subtleties, using Json.Net or is it a bug?

For this code
var s = JsonConvert.SerializeObject(instance);
var desInst = JsonConvert.DeserializeObject<ClassWithParams>(s);
Your json will be {"PropertWithBackingField":[{"ParamOne":1}]}
But you say to include private field in serialization/deserialization with
contractResolver.DefaultMembersSearchFlags |= BindingFlags.NonPublic;
and get a json
{
"_privateFieid": [
{
"ParamOne": 1
}
],
"PropertWithBackingField": [
{
"ParamOne": 1
}
]
}
So there are two deserializations, one for _privateFieid and one for PropertWithBackingField
Either use BindingFlags.Public or use my code above with is much simpler.

DeserializeInstance method receives existing instance as argument. Probably it does not creates new instance but fills in existing and returns it.
Try to put ReferenceEquals(instance, deserializedInstance) to your watch. To avoid data duplicating use overload that does not accepts existing instance or create new instance and deserialize it.

XML deserialization - throwing custom errors

So I have the following method:
private int? myIntField
[System.Xml.Serialization.XmlElementAttribute(Form = System.Xml.Schema.XmlSchemaForm.Unqualified)]
public int? IntField{
get {
return this.myIntField;
}
set {
this.myIntField= value;
}
}
Now, I am deserializing xml from a post, if for whatever reason I am getting a string, such as "here is the int field: 55444" instead of 55444, the error I get in response is: Input string was not in a correct format. which isn't very specific, especially considering I will have more than one int field I need to verify.
Originally, I was planning something like this:
private string myIntField
[System.Xml.Serialization.XmlElementAttribute(Form = System.Xml.Schema.XmlSchemaForm.Unqualified)]
public int? IntField{
get {
return this.myIntField.CheckValue();
}
set {
this.myIntField= value;
}
}
Where CheckValue performs a try-parse to an Int32, and if it fails it returns a null and adds an error to a list. However, I can't seem to nail this set-up for the generated classes.
Is there I way I can throw a specific error if I am getting strings in place of ints, DateTimes, etc?

It's easy if you have schema(s) for you XML and validate it against schema before deserializing. Suppose you have schema(s) for your XML, you can initialize a XmlSchemaSet, add your schema(s) in it and the:
var document = new XmlDocument();
document.LoadXml(xml); // this a string holding the XML
document.Schemas.XmlResolver = null; //if you don't need to resolve every references
document.Schemas.Add(SchemaSet); // System.Xml.Schema.XmlSchemaSet instance filled with schemas
document.Validate((sender, args) => { ... }); //args are of type ValidationEventArgs and hold problem if there is one...
Personally I think this is a better approach, because you can validate your XML before deserializing and be sure the XML is correct otherwise the deserializer will most probably throw an exception if something is wrong and you will almost never be able to show a meaningful feedback to the user...
P.S. I recommend creating schema(s) describing the XML

The "Input string was not in a correct format" messages comes from a standard System.FormatException raised by a call to int.Parse, added to the automatically generated assembly that does the deserialization. I don't think you can add some custom logic to that.
One solution is to do something like this:
[XmlElement("IntField")]
[Browsable(false)] // not displayed in grids
[EditorBrowsable(EditorBrowsableState.Never)] // not displayed by intellisense
public string IntFieldString
{
get
{
return DoSomeConvert(IntField);
}
set
{
IntField = DoSomeOtherConvert(value);
}
}
[XmlIgnore]
public int? IntField { get; set; }
It's not perfect, because you can still get access to the public IntFieldString, but at least, the "real" IntField property is used only programmatically, but not by the XmlSerializer (XmlIgnore), while the field that's holding the value back & forth is hidden from programmers (EditorBrowsable), grids (Browsable), etc... but not from the XmlSerializer.

I have three approaches for you.
Assuming your data is being entered by a user in a user interface, use input validation to ensure the data is valid. It seems odd to allow random strings to be entered when it should be an integer.
Use exactly the approach you suggest above. Here's an example using LINQ Pad
void Main()
{
using(var stream = new StringReader(
"<Items><Item><IntValue>1</IntValue></Item></Items>"))
{
var serializer = new XmlSerializer(typeof(Container));
var items = (Container)serializer.Deserialize(stream);
items.Dump();
}
}
[XmlRoot("Items")]
public class Container
{
[XmlElement("Item")]
public List<Item> Items { get; set; }
}
public class Item
{
[XmlElement("IntValue")]
public string _IntValue{get;set;}
[XmlIgnore]
public int IntValue
{
get
{
// TODO: check and throw appropriate exception
return Int32.Parse(_IntValue);
}
}
}
Take control of serialization using IXmlSerializable, here's another example
void Main()
{
using(var stream = new StringReader(
"<Items><Item><IntValue>1</IntValue></Item></Items>"))
{
var serializer = new XmlSerializer(typeof(Container));
var items = (Container)serializer.Deserialize(stream);
items.Dump();
}
}
[XmlRoot("Items")]
public class Container
{
[XmlElement("Item")]
public List<Item> Items { get; set; }
}
public class Item : IXmlSerializable
{
public int IntValue{get;set;}
public void WriteXml (XmlWriter writer)
{
writer.WriteElementString("IntValue", IntValue.ToString());
}
public void ReadXml (XmlReader reader)
{
var v = reader.ReadElementString();
// TODO: check and throw appropriate exception
IntValue = int.Parse(v);
}
public XmlSchema GetSchema()
{
return(null);
}
}