Dynamically convert class property name while converting to json using the values of another class

Question

I have two classes

// contains names/keys for JSON serialization
public class Mapping
{
    public string Id { get; set; }
    public string Name { get; set; }
}

// contains values for JSON serialization
public class Data
{
    public string Id { get; set; }
    public string Name { get; set; }
}

var map = new Mapping { Id = "Code", Name = "Tiltle" };
var data = new Data { Id = "Test1234", Name = "testname1234" };

so when data is serialized using the mapping from map, JSON should look like this

{
   "Code":"Test1234"
   "Tiltle":"testname1234"
}

But your question is really not clear, what is Test1? Please explain your question better. — DavidG
– DavidG, Commented Mar 20, 2020 at 9:59
These are the 2 classes want to use one class values to define property name for other while converting to json — Coder
– Coder, Commented Mar 20, 2020 at 10:07
This seems like a really peculiar thing to do. Perhaps you're just better off using a Dictionary? — DavidG
– DavidG, Commented Mar 20, 2020 at 10:08
As @DavidG wrote, this feels like a xy problem. It's likely that you should represent this data using a dictionary internally, and then simply serialize the dictionary. — vgru
– vgru, Commented Mar 20, 2020 at 10:19

weichch · Accepted Answer · 2020-03-20 10:13:05Z

You need a custom JsonConverter and because your map object is created at runtime (I suppose), the converter has to be created at runtime as well.

Try:

var settings = new JsonSerializerSettings();
settings.Converters.Add(new PropertyNameFromMapTypeJsonConverter(map, typeof(Test2)));
var json = JsonConvert.SerializeObject(Data, settings);

The converter:

class PropertyNameFromMapTypeJsonConverter : JsonConverter
{
    private readonly IDictionary<string, object> _mappings;
    private readonly Type _targetType;

    public PropertyNameFromMapTypeJsonConverter(object mapObj, Type targetType)
    {
        // mapobj is instance of Test1
        // Use reflection to create a dictionary used as mappings between Test1 and 2
        _mappings = TypeDescriptor.GetProperties(mapObj)
            .OfType<PropertyDescriptor>()
            .ToDictionary(prop => prop.Name, prop => prop.GetValue(mapObj));

        _targetType = targetType;
    }

    public override bool CanConvert(Type objectType)
    {
        return objectType == _targetType;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        // Do not support deserialize
        throw new NotSupportedException();
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var dict = TypeDescriptor.GetProperties(value)
            .OfType<PropertyDescriptor>()
            .ToDictionary(prop => _mappings[prop.Name], prop => prop.GetValue(value));

        serializer.Serialize(writer, dict);
    }
}

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