Custom conversion of specific objects in JSON.NET

Question

I'm using JSON.NET to serialize some of my objects, and i'd like to know if there is a simple way to override the default json.net converter only for a specific object?

Currently I have the following class:

public class ChannelContext : IDataContext {     public int Id { get; set; }     public string Name { get; set; }     public IEnumerable<INewsItem> Items { get; set; } } 

JSON.NET currently serializes the above like:

{     "Id": 2,     "Name": "name value",     "Items": [ item_data_here ] } 

Is it possible just for that specific class to format it this way instead:

"Id_2": {     "Name": "name value",     "Items": [ item data here ] } 

I'm kinda new to JSON.NET.. I was wondering if the above has something to do with writing a custom converter. I wasn't able to find any concrete examples on how to write one, If anyone can point me out to a specific source, I'll really appreciate it.

I need to find a solution which makes that specific class always convert the same, because the above context is a part of an even bigger context which the JSON.NET default converter converts just fine.

Hope my question is clear enough...

UPDATE:

I've found how to create a new custom converter (by creating a new class which inherits from JsonConverter and override it's abstract methods), I overriden the WriteJson method as follows:

public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)     {         ChannelContext contextObj = value as ChannelContext;          writer.WriteStartObject();         writer.WritePropertyName("id_" + contextObj.Id);         writer.WriteStartObject();         writer.WritePropertyName("Name");         serializer.Serialize(writer, contextObj.Name);          writer.WritePropertyName("Items");         serializer.Serialize(writer, contextObj.Items);         writer.WriteEndObject();         writer.WriteEndObject();     } 

This indeed does the job successfully, but... I'm intrigued if there's a way to serialize the rest of the object properties by reusing the default JsonSerializer (or converter for that matter) instead of manually "Writing" the object using the jsonwriter methods.

UPDATE 2: I'm trying to get a more generic solution and came up with the following:

public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)     {         writer.WriteStartObject();          // Write associative array field name         writer.WritePropertyName(m_FieldNameResolver.ResolveFieldName(value));          // Remove this converter from serializer converters collection         serializer.Converters.Remove(this);          // Serialize the object data using the rest of the converters         serializer.Serialize(writer, value);          writer.WriteEndObject();     } 

This works fine when adding the converter manually to the serializer, like this:

jsonSerializer.Converters.Add(new AssociativeArraysConverter<DefaultFieldNameResolver>()); jsonSerializer.Serialize(writer, channelContextObj); 

But doesn't work when using the [JsonConverter()] attribute set to my custom coverter above the ChannelContext class because of a self reference loop that occurs when executing:

serializer.Serialize(writer, value) 

This is obviously because my custom converter is now considered the default converter for the class once it is set with the JsonConverterAttribute, so I get an inifinite loop. The only thing I can think of, in order to solve this problem is inheriting from a basic, jsonconverter class, and calling the base.serialize() method instead... But is such a JsonConverter class even exists?

Thanks a lot!

Mikey

Answer 1

If anyone's interested in my solution:

When serializing certain collections, I wanted to create an associative json array instead of a standard json array, so my colleague client side developer can reach those fields efficiently, using their name (or key for that matter) instead of iterating through them.

consider the following:

public class ResponseContext {     private List<ChannelContext> m_Channels;      public ResponseContext()     {         m_Channels = new List<ChannelContext>();     }      public HeaderContext Header { get; set; }      [JsonConverter(         typeof(AssociativeArraysConverter<ChannelContextFieldNameResolver>))]     public List<ChannelContext> Channels     {         get { return m_Channels; }     }  }  [JsonObject(MemberSerialization = MemberSerialization.OptOut)] public class ChannelContext : IDataContext {     [JsonIgnore]     public int Id { get; set; }      [JsonIgnore]     public string NominalId { get; set; }      public string Name { get; set; }      public IEnumerable<Item> Items { get; set; } } 

Response context contains the whole response which is written back to the client, like you can see, it includes a section called "channels", And instead of outputting the channelcontexts in a normal array, I'd like to be able to output in the following way:

"Channels" { "channelNominalId1": {   "Name": "name value1"   "Items": [ item data here ] }, "channelNominalId2": {   "Name": "name value2"   "Items": [ item data here ] } } 

Since I wanted to use the above for other contexts as well, and I might decide to use a different property as their "key", or might even choose to create my own unique name, which doesn't have to do with any property, I needed some sort of a generic solution, therefore I wrote a generic class called AssociativeArraysConverter, which inherits from JsonConverter in the following manner:

public class AssociativeArraysConverter<T> : JsonConverter     where T : IAssociateFieldNameResolver, new() {     private T m_FieldNameResolver;      public AssociativeArraysConverter()     {         m_FieldNameResolver = new T();     }      public override bool CanConvert(Type objectType)     {         return typeof(IEnumerable).IsAssignableFrom(objectType) &&                 !typeof(string).IsAssignableFrom(objectType);     }      public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)     {         IEnumerable collectionObj = value as IEnumerable;          writer.WriteStartObject();          foreach (object currObj in collectionObj)         {             writer.WritePropertyName(m_FieldNameResolver.ResolveFieldName(currObj));             serializer.Serialize(writer, currObj);         }          writer.WriteEndObject();     } } 

And declared the following Interface:

public interface IAssociateFieldNameResolver {     string ResolveFieldName(object i_Object); } 

Now all is left to do, is create a class which implements IAssociateFieldNameResolver's single function, which accepts each item in the collection, and returns a string based on that object, which will act as the item's associative object's key.

Example for such a class is:

public class ChannelContextFieldNameResolver : IAssociateFieldNameResolver {     public string ResolveFieldName(object i_Object)     {         return (i_Object as ChannelContext).NominalId;     } }