Convert MongoDB BsonDocument to valid JSON in C#

Question

I am working with the MongoDB C# driver. I have a BsonDocument with some data which includes some MongoDB-specific types (like ObjectIDs and ISODates). I want t

Answer 1

Through experimentation I discovered that there is an option that makes this method output proper JSON:

BsonDocument myBsonDocument = ... //code that loads a BSON document
myBsonDocument.ToJson(new JsonWriterSettings { OutputMode = JsonOutputMode.RelaxedExtendedJson})

Result:

{ "_id" : { "$oid" : "5fb7a33e73152101d6610e9d" }, "moreProperties" : "moreValues" }

Answer 2

what about

String json = result.toJson(JsonWriterSettings.builder().objectIdConverter(new Converter<ObjectId>() {
            @Override
            public void convert(ObjectId value, StrictJsonWriter writer) {
                writer.writeString(value.toHexString());
            }
        }).build());

Answer 3

I've ran into the same thing, you can get valid JSON via:

var jsonWriterSettings = new JsonWriterSettings { OutputMode = JsonOutputMode.Strict };
JObject json = JObject.Parse(postBsonDoc.ToJson<MongoDB.Bson.BsonDocument>(jsonWriterSettings));

However it will return something like:

{"_id":{"$oid":"559843798f9e1d0fe895c831"}, "DatePosted":{"$date":1436107641138}}

I'm still trying to find a way to flatten that.

Answer 4

Here is the way i did it, to skip mongodb _id entry.

var collection = _database.GetCollection<BsonDocument>("test");

var result = await collection.Find(new BsonDocument())
     .Project(Builders<BsonDocument>.Projection.Exclude("_id"))
     .ToListAsync();
var obj = result.ToJson();

Answer 5

If you need to use this ASP.NET Core for when you may be returning a model that has BsonDocument to be able to add dynamic data. You can use this JsonConverter implementation based on MarkKGreenway's answer!

 public class BsonDocumentJsonConverter : JsonConverter
    {
        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(BsonDocument);
        }

        public override bool CanRead
        {
            get
            {
                return false;
            }
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            throw new NotImplementedException();
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            //string json = (value as BsonDocument).ToJson(); //!NB: this returns BSON not JSON. Why on earth is it called ToJson!?
            string json = JsonConvert.SerializeObject(value);
            writer.WriteRawValue(json);
        }
    }

Then in your Startup.cs just add the following.

  services.AddMvc()
                .AddJsonOptions(options => options.SerializerSettings.Converters.Add(new BsonDocumentJsonConverter()));

Answer 6

My problem had to do with how DotNet Core WebAPI serializes an object to json. If you return a string from a method that is formatted as json, WEBAPI will serialize it to json again. This is only needed if you are working with a generic BsonDocument to save to MongoDb.

[HttpGet()]
[ProducesResponseType(StatusCodes.Status200OK)]
public async Task<ActionResult<string>> GetAsync()
{
    return Ok(ret.ToJson());
}

Fix

[HttpGet()]
[ProducesResponseType(StatusCodes.Status200OK)]
public async Task<ActionResult<object>> GetAsync()
{
    var doc = await _collection.Find(...).FirstOrDefaultAsync();
    return Ok(JObject.Parse(doc.ToJson()));
}