.NET serialization of JSON data with dynamic structure (schema)

Question

The web service I consume responces with json data.

it gives resultObject as array: resultObject:[{object1}, {object2},...] if there more then one object and it returns resultObject:{object1 } if there only one object.

for serializing in .NET I created a "static" structure of classes to map json schema. But if in one case i've got an array (list) of objects an in other case just one object, how is it possible to handle this situation?

Answer 1

I have found a plethora of ugly solutions to this one, but so far goes:

If you use the System.Web.Script.Serialization.JavaScriptSerializer you have very limited control. If the result data type is simple, you could simply use the DeserializeObject method; it will translate everything into Dictionary and the "resultObject" property will in the first case be a Dictionary while the latter case will turn it into an array of such dictionary. It will not save you the headache of the final translation, but you will get the data into dictionaries which could be considered a first step.

I also attempted to use the KnownTypes and the DataContractJsonSerializer, but alas the datacontract serializer needs "hints" in the form of specially named properties to aid it deserializing. ( Why am I using the KnownType attribute wrong? ). This is a hopeless strategy if you don't have any control of the serialization which I guess is the case for you.

So now we are down to the butt-ugly solutions of which trial-and-error is my first choice: When using the ScriptSerializer the conversion will fail with an InvalidOperationException if anything is wrong. I then created two data types one with data-as-arrays and one where data is a single instance (the DataClass is my invention since you do not specify the data types):

    [DataContract]
    public class DataClass
    {
        [DataMember]
        public string FirstName { get; set; }
        [DataMember]
        public int BirthYear { get; set; }

        public override string ToString()
        {
            return "FirstName : '" + FirstName + "', BirthYear: " + BirthYear;
        }
    }

    [DataContract]
    public class ResultSingle 
    {
        [DataMember]
        public DataClass Data { get; set; }
    }

    [DataContract]
    public class ResultArray 
    {
        [DataMember]
        public List<DataClass> Data { get; set; }
    }

Using these data types it is possible to translate using

        JavaScriptSerializer jSer = new JavaScriptSerializer();
        var one = jSer.Deserialize<ResultSingle>(jsonWithSingleInstance);
        var many = jSer.Deserialize<ResultArray>(jsonWithArray);

But this of course require you to known the data type in advance and you get two different result types. Instead you could choose to always convert to ResultArray. If you get an exception you should convert as ResultSingle and then instantiate the ResultArray and manually add the data object to the Data list:

    static ResultArray ConvertJson(string json)
    {
        ResultArray fromJson;
        JavaScriptSerializer jSer = new JavaScriptSerializer();
        try
        {
            fromJson = jSer.Deserialize<ResultArray>(json);
            return fromJson;
        }
        catch (InvalidOperationException)
        {
            var single = jSer.Deserialize<ResultSingle> (json);
            fromJson = new ResultArray();
            fromJson.Data = new List<DataClass>();
            fromJson.Data.Add(single.Data);
            return fromJson;
        }
    }

    static void Main(string[] args)
    {
        var jsonWithSingleInstance = "{\"Data\":{\"FirstName\":\"Knud\",\"BirthYear\":1928}}";
        var jsonWithArray = "{\"Data\":[{\"FirstName\":\"Knud\",\"BirthYear\":1928},{\"FirstName\":\"Svend\",\"BirthYear\":1930}]}";

        var single = ConvertJson(jsonWithSingleInstance);
        var array = ConvertJson(jsonWithArray);
    }

I do not say this is a beautiful solution (it isn't), but it should do the job.

You could also look at json.net which seem to be the json serializer of choice in .NET: How to install JSON.NET using NuGet?

Answer 2

Well, my service provider finally said that it is really a bug.

http://jira.codehaus.org/browse/JETTISON-102

says that is it because of java version that they use.