Mongodb C# Exception Cannot Deserialize String from Bsontype Int32

mongodb C# exception Cannot deserialize string from BsonType Int32

Yes, String property in C# object has Int32 value in mongo storage, so you have exception during serialization (see code for MongoDB.Bson.Serialization.Serializers.BsonStringSerializer class).

1) You can define your own serializer, which will deserialize Int32 values to string property as well as String ones. Here it is:

public sealed class StringOrInt32Serializer : BsonBaseSerializer
public override object Deserialize(BsonReader bsonReader, Type nominalType,
Type actualType, IBsonSerializationOptions options)
var bsonType = bsonReader.CurrentBsonType;
switch (bsonType)
case BsonType.Null:
return null;
case BsonType.String:
return bsonReader.ReadString();
case BsonType.Int32:
return bsonReader.ReadInt32().ToString(CultureInfo.InvariantCulture);
var message = string.Format("Cannot deserialize BsonString or BsonInt32 from BsonType {0}.", bsonType);
throw new BsonSerializationException(message);

public override void Serialize(BsonWriter bsonWriter, Type nominalType,
object value, IBsonSerializationOptions options)
if (value != null)

Then mark necessary properties (which have different types in MongoDB in your opinion) with this serializer, for example:

public string Body { get; set; }

Also I've found very similar question here: Deserializing field when type is changed using MongoDb csharp driver

2) The second approach - is to 'normalize' your data in storage: convert all integer field values to string. So, you should change field $type from 16 (32-bit integer) to 2 (string). See BSON types. Let's do it for body field:

db.train.find({ 'body' : { $type : 16 } }).forEach(function (element) {   
element.body = "" + element.body; // Convert field to string;

Cannot deserialize string from BsonType ObjectId in MongoDb C#

Instead of using

ed.Id = Guid.NewGuid().ToString();

I used

ed.Id = MongoDB.Bson.ObjectId.GenerateNewId().ToString();

For generating Id

Its working fine : )

FormatException: Cannot deserialize a 'Guid' from BsonType 'ObjectId'

Apparently, the GUIDs I was using were not valid GUIDs. I generated them using an online generator.

I generated new ones on another website, and voilá. Everyting worked.

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