Flatten [BsonExtraElements] to key value pair json output

Question

I am using [BsonExtraElements] in c# to capture additional data that cannot be mapped to my class.

public class QuestionAnswerClass
{
    public string Name { get;set;}
  
    [BsonExtraElements]
    public Dictionary<string,object> AdditionalData {get; set;}
}

Sample data stored in mongodb

{
 Name: John
 Question1: Answer1
 Question2: Answer2
},
{
 Name: Mary
 Question3: Answer3
 Question4: Answer4
}
 

In my controller, I get the data mongoDB, deserialize it to my QuestionAnswerClass and return output as a JsonResult.

var client = new MongoClient("Credentials here");
var database = client.GetDatabase("db");

var results = database.GetCollection<QuestionAnswerClass>("QuestionAnswers").AsQueryable().ToList();
return new JsonResult(results);

Json output is as follow

[
 {
  Name: John
  AdditionalData: {
    Question1: Answer1,
    Question2: Answer2
  }, 
 {
  Name: Mary
  AdditionalData: {
    Question3: Answer3,
    Question4: Answer4
  },
 }
]

Question: How can I flatten the output of AdditionalData to it's own keyvaluepair. Example output that I want is below

[
 {
  Name: John,
  Question1: Answer1,
  Question2: Answer2
 }, 
 {
  Name: Mary,
  Question3: Answer3,
  Question4: Answer4 
 }
]

Answer 1

System.Text.Json (and JSON.NET for anyone else reading) supports an attribute called [JsonExtensionData].

You can declare it like this in your model:

[JsonExtensionData]
public Dictionary<string, object> ExtensionData { get; set; }

And it will serialize the dictionary key/values as properties in the parent object. So if we take your object and add this attribute:

public class QuestionAnswerClass
{
    public string Name { get;set;}
  
    [JsonExtensionData]
    [BsonExtraElements]
    public Dictionary<string,object> AdditionalData {get; set;}
}

We'll get the expected output:

[
  {
    "Name": "John",
    "Question1": "Answer1",
    "Question2": "Answer2"
  },
  {
    "Name": "Mary",
    "Question3": "Answer3",
    "Question4": "Answer4"
  }
]

Try it online