Question posted in Json
Our archive of expertly curated questions and answers provides insights and solutions to common problems related to this popular data interchange format. From parsing and manipulating JSON data to integrating it with various programming languages and web services, our archive has got you covered. Start exploring today and take your JSON skills to the next level

Deserialize json with dynamic number of objects and keys

ErikThysell
March 7, 2023
175 views
0 votes
2 Answers

I have a json string that I need to deserialize (in a WPF app, using System.Net.Json). A subobject (node) in the tree contains a variable number of propertiers/nodes with variable names.
A "minimal" sample looks like this:

"intervals": [{
"timestamp": 1677477728,
"123456": {
"subintervals": [{
"max": "56.7",
"label": "Leq"
}, {
"max": "58.1",
"label": "Lmax"
}
] }
}, {
"timestamp": 1677477730,
"54321": {
"subintervals": [{
"value": "58.5",
"label": "Leq"
}, {
"value": "59.5",
"label": "Lmax"
}
] },
"56789": {
"subintervals": [{
"value": "78.2",
"label": "Lmax"
}, {
"value": "74.3",
"label": "Leq"
}
] }
} ]

I.e. a an array "intervals" with a "timestamp" and a varying number of objects/nodes that has a number-string as key.

With the following

public class IntervalMeta
    {
        public long? Timestamp { get; set; }
        [JsonExtensionData]
        public Dictionary<string, JsonElement>? MeasurementPoints { get; set; } = new();
    }

that gives a dictionary with JsonElements that I can step through and look for the desired properties. It would though be nice with a

public Dictionary<string, SubInterval[]>? MeasurementPoints { get; set; } = new();

where SubInterval :

public class SubInterval
    {
        public string? Max { get; set; }
        public string? Label { get; set; }
    }

I am hoping and trying to make a custom JsonConverter that I could use but there are a number of issues that I don’t know how to handle:
Issue 0: how do I get it to use the custom JsonConverter?

My try for a converter:

public class MeasurementPointDictionaryJsonConverter : JsonConverter<Dictionary<string, SubInterval>>
    {
        public override Dictionary<string, SubInterval[]>? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
        {
            var dict = new Dictionary<string, SubInterval[]>();
            // Issue 3: How do loop over the contents in the Interval node (containing 0 or more SubIntervals)
            while (reader.Read())
            {
                // Issue 1: How do I read the key?
                var measurementPointId = reader.GetString();
                // Issue 2: How do I deserialize the node to a SubInterval?
                string value = reader.GetString();
                var intervals = JsonSerializer.Deserialize<SubInterval[]>(value, options);
                
                dict.Add(measurementPointId ?? "", intervals ?? new());
            }
            return dict;
        }

        public override void Write(Utf8JsonWriter writer, Dictionary<string, SubInterval[]> value, JsonSerializerOptions options)
        {
            throw new NotImplementedException();
        }
    }

I have tried just decorating the MeasurementPoints with:

[JsonConverter(typeof(MeasurementPointDictionaryJsonConverter))]
public Dictionary<string, SubInterval[]>? MeasurementPoints { get; set; } = new();

but that just result in MeasurementPoints == null. Adding the JsonExtensionData attribute:

[JsonExtensionData]
[JsonConverter(typeof(MeasurementPointDictionaryJsonConverter))]
public Dictionary<string, SubInterval[]>? MeasurementPoints { get; set; } = new();

Throws an error when trying to deserialize (seems that the JsonExtensionData can only handle Dictionary<string, JsonElement> or Dictionary<string,object>).

Any help would be most appreciated (I have asked chatgtp but I didn’t give me much more 🙂 ).

EDIT: Corrected SubInterval => SubIntervals[]. Kudos to @KJanec

Tags: c#dynamic json jsonconverter system.text.json

Answers

I come up with something like this.

But before that I want to note that in your dictionary you don’t have singular SubInterval but collection of SubInterval. Correct me if I’m wrong.

Converter:

 public class CustomConverter : JsonConverter<List<IntervalMeta>>
    {
        public override List<IntervalMeta> Read(ref Utf8JsonReader reader, Type typeToConvert,
            JsonSerializerOptions options)
        {
            using var jsonDocument = JsonDocument.ParseValue(ref reader);
            var root = jsonDocument.RootElement;

            var intervals = root.GetProperty("intervals").EnumerateArray();

            var values = new List<IntervalMeta>();

            foreach (var interval in intervals)
            {
                var item = new IntervalMeta();

                    
                foreach (var property in interval.EnumerateObject())
                {
                    if (property.Name == "timestamp")
                    {
                        if (property.Value.TryGetInt64(out var value))
                        {
                            item.Timestamp = value;
                        }
                    }
                    else
                    {
                        var key = property.Name;


                        var enumerateObject = property.Value.EnumerateObject();
                        if (!enumerateObject.Any()) continue;

                        var subIntervalArray = enumerateObject.First();

                        var subIntervalsJson = subIntervalArray.Value.GetRawText();

                        var subIntervals = JsonSerializer.Deserialize<SubInterval[]>(subIntervalsJson,
                            new JsonSerializerOptions()
                            {
                                PropertyNameCaseInsensitive = true
                            });

                        item.MeasurementPoints.Add(key, subIntervals);
                    }
                }

                values.Add(item);
            }

            return values;
        }

        public override void Write(Utf8JsonWriter writer, List<IntervalMeta> value, JsonSerializerOptions options)
        {
            throw new NotImplementedException();
        }
    }

Rest of code that I used for tests:

public class IntervalMeta
{
    public long? Timestamp { get; set; }

    public Dictionary<string, SubInterval[]> MeasurementPoints { get; set; } = new();
}

public class SubInterval
{
    public string Max { get; set; }
    public string Label { get; set; }
}

class Program
{
    static async Task Main(string[] args)
    {
        var input = @"
        {
           ""intervals"":[
              {
                 ""timestamp"":1677477728,
                 ""123456"":{
                    ""subintervals"":[
                       {
                          ""max"":""56.7"",
                          ""label"":""Leq""
                       },
                       {
                          ""max"":""58.1"",
                          ""label"":""Lmax""
                       }
                    ]
                 }
              },
              {
                 ""timestamp"":1677477730,
                 ""54321"":{
                    ""subintervals"":[
                       {
                          ""value"":""58.5"",
                          ""label"":""Leq""
                       },
                       {
                          ""value"":""59.5"",
                          ""label"":""Lmax""
                       }
                    ]
                 },
                 ""56789"":{
                    ""subintervals"":[
                       {
                          ""value"":""78.2"",
                          ""label"":""Lmax""
                       },
                       {
                          ""value"":""74.3"",
                          ""label"":""Leq""
                       }
                    ]
                 }
              }
           ]
        }";

        var test = JsonSerializer.Deserialize<List<IntervalMeta>>(input, new JsonSerializerOptions
        {
            Converters = { new CustomConverter() },
            PropertyNameCaseInsensitive = true
        });

    }

EDIT:

I firstly solved using Newtonsoft because I more familiar with and then converted to System.Text.Json. But I see that Serge added answer in Newtonsoft. However I solved a little diffrent using CustomCreationConverter, so I think it is worth sharing.

var list = JsonConvert.DeserializeObject<List<IntervalMeta>>(input, new CustomConverter());

public class CustomConverter : CustomCreationConverter<List<IntervalMeta>>
{
    public override List<IntervalMeta> Create(Type objectType)
    {
        return new List<IntervalMeta>();
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer)
    {
        JObject jObject = JObject.Load(reader);

        IList<JToken> intervals = jObject["intervals"].Children().ToList();

        return intervals.Select(jToken =>
        {
            var item = new IntervalMeta();

            foreach (var jProperty in jToken.OfType<JProperty>())
            {
                if (jProperty.Name == "timestamp")
                {
                    if (long.TryParse(jProperty.Value.ToString(), out var value))
                    {
                        item.Timestamp = value;
                    }

                    continue;
                }

                var key = jProperty.Name;

                var jPropertyValue = jProperty.Value.First.First;
                var subinternvalDictionary = jPropertyValue.ToObject<SubInterval[]>();
                item.MeasurementPoints.Add(key, subinternvalDictionary);
            }


            return item;
        }).ToList();
    }
}

you can try this converter

using Newtonsoft.Json

List<Interval> intervals=JsonConvert.DeserializeObject<List<Interval>>(json,new DictToListConverter());

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

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var jObj = JObject.Load(reader);
        
        return  jObj["intervals"].Select(x => GetInterval((JObject)x)).ToList();
                               
    }

    public override bool CanConvert(Type objectType)
    {
        return true;
    }
    public  Interval GetInterval(JObject jObj)
    {
        var interval = jObj.ToObject<IntervalTemp>();
        interval.subintervals = new List<SubintervalItem>();

        foreach (var item in interval.dict)
        {
            var sii = new SubintervalItem { name = item.Key, subintervals = new List<Subinterval>() };
            sii.subintervals = item.Value["subintervals"].Select(d => d.ToObject<Subinterval>()).ToList();
            interval.subintervals.Add(sii);
        }

        return JObject.FromObject(interval).ToObject<Interval>();

        //or if a performance is an issue
        //interval.dict = null;
        //return interval;
    }
}

classes

public class IntervalTemp : Interval
{
    [JsonExtensionData]
    public Dictionary<string, JToken> dict { get; set; }
    
}
public class Interval
{
    public long timestamp { get; set; }
    public List<SubintervalItem> subintervals { get; set; }
}
public class SubintervalItem
{
    public string name { get; set; }
    public List<Subinterval> subintervals { get; set; }
}

public class Subinterval
{
    public string max { get; set; }
    public string label { get; set; }
    public string value { get; set; }
}

Please signup or login to give your own answer.

Click here to cancel reply.