How to get parent property name in System.Text.Json.Serialization.JsonConverter? - json

Question

I'm dealing with a 3rd Party API that returns data like this:
{
"dynamicFields": {
"prop1": "val1",
"prop2": "val2",
"prop3": "val3"
},
// otherFields ...
}
Since these "dynamic fields" are not strongly typed. I want to represent my POCO as:
class ApiResponse {
public DynamicFields DynamicFields { get; get; }
}
class DynamicFields {
public Dictionary<string, string> Values { get; set; }
}
The rub is, I want to be able to prefix the keys in the dictionary, such that they have the parent property name like so:
{
"DynamicFields": {
"dynamicFields.prop1": "val1",
"dynamicFields.prop2": "val2",
"dynamicFields.prop3": "val2",
}
}
However, it doesn't look like System.Text.Json.Serialization.JsonConverter<T> gives me access to the parent property name. Is there another way to accomplish this such that I can get the desired output? I'm really trying to not use Newtonsoft/Json.NET as I believe System.Text.Json is "the future".
class DynamicFieldConverter : JsonConverter<DynamicField>
{
public override DynamicField Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
// How do I get the name of the parent property here?
...
}
public override void Write(Utf8JsonWriter writer, DynamicField value, JsonSerializerOptions options)
{
...
}
}

Answer 1

Here my solution for your case:
DynamicFieldConverter class
public class DynamicFieldConverter : JsonConverter<DynamicFields>
{
private const string MainPropName = "dynamicFields";
public override DynamicFields Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
var dictionary = new Dictionary<string, string>();
var startDepth = reader.CurrentDepth;
while (reader.Read())
{
if (reader.TokenType == JsonTokenType.EndObject && reader.CurrentDepth == startDepth)
{
return new DynamicFields
{
Values = dictionary
};
}
if (reader.TokenType == JsonTokenType.PropertyName)
{
var propertyName = reader.GetString();
if(propertyName == MainPropName)
continue;
var value = JsonSerializer.Deserialize<string>(ref reader, options);
dictionary.Add($"{MainPropName}.{propertyName}", value);
}
}
throw new JsonException();
}
public override void Write(Utf8JsonWriter writer, DynamicFields value, JsonSerializerOptions options)
{
}
}
JsonConverterAttribute for class
[JsonConverter(typeof(DynamicFieldConverter))]
public class DynamicFields
{
public Dictionary<string, string> Values { get; set; }
}
Finally, console to test it
static void Main(string[] args)
{
var json = "{\r\n \"dynamicFields\": {\r\n \"prop1\": \"val1\",\r\n \"prop2\": \"val2\",\r\n \"prop3\": \"val3\"\r\n }\r\n}";
var obj = JsonSerializer.Deserialize<DynamicFields>(json);
}