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Reputation: 2263

Unable to cast object of type 'MongoDB.Bson.BsonDocument' to type 'MongoDB.Bson.BsonBinaryData'

I'm trying to generate a Bson from Json. I tried using Json.Net but there seems to be a documented behavior where the library produces uint64 for integer fields. unfortunately we must use uint32.

Hence I'm trying to use mongodb bson library. but I can't figure how to convert a BsonDocument into a BsonBinaryData.

//Works well, I can inspect with watch
MongoDB.Bson.BsonDocument doc = MongoDB.Bson.BsonDocument.Parse(json);

//Invalid cast exception
byte[] data = doc.AsByteArray;

Upvotes: 4

Views: 2950

Answers (1)

MarkusParker
MarkusParker

Reputation: 1596

To get the raw byte array representation of a BsonDocument instance, use the extension method ToBson(). To create a BsonDocument from the byte array representation, create an instance of RawBsonDocument, which is derived from BsonDocument and takes a byte array as constructor argument.

Here is an example for using two bson documents to pass parameters to a native c function call and retrieve the result:

public static BsonDocument CallCFunction(BsonDocument doc) {
  byte[] input = doc.ToBson();
  int length = input.Length;
  IntPtr p = DllImportClass.CFunction(ref length, input);
  if (p == IntPtr.Zero) {
    // handle error
  }
// the value of length is changed in the c function
  var output = new byte[length]; 
  System.Runtime.InteropServices.Marshal.Copy(p, output, 0, length);
  return new RawBsonDocument(output);
}

Note that the memory p points to must somehow be freed.

Upvotes: 2

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