Newtonsoft JsonConverter - Json Structure Changes per item in collection

Question

I need a JsonConverter that can handle the following Json Structure. I always want back the segment model for each object in the "segments" collection in the Json. The problem I am having is how to handle the multiple structures in the Json. I am somewhat familiar with writing JsonConverters but this one has me stumped. I asked the partner we are working with if it was possible to standardize the response and was told no.

{ 
    "segments": [ 
        { 
            "headers" : 
            { 
                "agent":"000000000049",
                "end_use":"consumer"
            }, 
            "data" : { 
                "vsd_id": "FI_444_56", 
                "name": "Filler Segment 4inx4inx2in", 
                "price":"00900", 
                "lead_time":"4-6"
                "certificate": "BR22"
            }
        }, 
        {
            "vsd_id": "RB_190_01", 
            "name": "Rod Backer 94in", 
            "price":"05000", 
            "lead_time":"4-6"
            "certificate": "BR23"
        }
    ]
}

public class SegmentRepository { 

    private Newtonsoft.Json.JsonSerializer _serializer;
    private HttpClient _client;

    public async Task<IList<Segment>> GetSegments(....) 
    { 
        // more code here that builds the requestMessage. not important

        using (var responseMessage = await _client.SendAsync(requestMessage))
        using (var content = await responseMessage.Content.ReadAsStreamAsync())
        using (var textReader = new StreamReader(content))
        using (var reader = new JsonTextReader(textReader))
        {
            var response = _serializer.Deserialize<Response>(reader);
            return response.Segments;
        }
    }
}

public class Response 
{ 
    [JsonProperty("segments")]
    public List<Segment> Segments {get;set;}
}

public class Segment 
{ 
    [JsonProperty("headers")]
    public Dictionary<string,string> Headers {get;set;}

    [JsonProperty("data")]
    public SegmentData Data {get;set;}
}

public class SegmentData 
{ 
    [JsonProperty("vsd_id")]
    public string Id {get;set;}
    
    [JsonProperty("name")]
    public string Name {get;set;}
    
    [JsonConverter(typeof(PriceConverter))]
    public Decimal Price {get;set;}
    
    [JsonProperty("lead_time")]
    [JsonConverter(typeof(LeadTime))]
    public LeadTime LeadTime {get;set;}

    [JsonProperty("certificate")]
    public string Certificate {get;set;}
}

NOTE: I have already asked the onwer of the API if they could standardize their responses and was told no.

So then.. what's the question? The data structure looks normal to me and it looks like you've built your models just fine. — Andy, Nov 08 '20 at 21:14
The Json changes between objects in the collection. take a look a the Json a bit closer. — Matt M, Nov 08 '20 at 21:25
But does it change between actual objects. If not, then you have 3 separate distinct models. It's normal. — Andy, Nov 08 '20 at 21:33
Make `Segment` and `SegmentData` inherit from some base class, say `SegmentBase`. Then you can create a custom `JsonConverter` as shown in [Deserializing polymorphic json classes without type information using json.net](https://stackoverflow.com/q/19307752/3744182), [Json.Net Serialization of Type with Polymorphic Child Object](https://stackoverflow.com/q/29528648/3744182) or [How to implement custom JsonConverter in JSON.NET to deserialize a List of base class objects?](https://stackoverflow.com/q/8030538/3744182). — dbc, Nov 10 '20 at 01:22
Basically the converter preloads into a `JObject` then checks the properties present to determine whether to deserialize to a `Segment` or `SegmentData`. — dbc, Nov 10 '20 at 01:23

score 0 · Accepted Answer · answered Nov 10 '20 at 19:43

I figured out how to do it. It's quite a simple solution once I figured it out. The piece I was missing for awhile was that I should decorate the class with the JsonCoverter attribute instead of a property.

[JsonConverter(typeof(SegmentsConverter))]
public class Segment
{
    [JsonProperty("headers")]
    public Dictionary<string, string> Headers { get; set; }

    [JsonProperty("data")]
    public SegmentData Data { get; set; }
}


public class SegmentsConverter : Newtonsoft.Json.JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return true;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;
        
        var jObject = JObject.Load(reader);

        if (FieldExists(jObject, "headers"))
        {
            var target = new Segment();
            serializer.Populate(jObject.CreateReader(), target);
            return target;
        }
        else
        {
            var container = new Segment();
            var data = new SegmentData();
            container.Data = data;
            serializer.Populate(jObject.CreateReader(), data);
            return container;
        }
    }


    private bool FieldExists(JObject jObject, string fieldName)
    {
        return jObject[fieldName] != null;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

Newtonsoft JsonConverter - Json Structure Changes per item in collection

1 Answers1