How to serialise / deserialise Mongo DB BSON Objects without Losing data in C#

Question

It seems that there are a few ways to serialise/ deserialise MongoDB data to/from objects

var docs = _collection.FindAs<MyType>(_document);

OR

BsonSerializer.Deserialize<MyType>(doc);

OR

var myClass = new Mytype();
myClass.Name = bsonDoc["name"].AsString;

I am wondering how to "use" the data in strongly types objects. But preserve the full Bsondocument - is it even possible? It seems that if I serialise into a strongly typed object and then saved it back - we would lose any information that wasn't in those objects.

Answer 1

In general, it is easiest to work with strongly-typed documents that map to your BSON structure in the collection. If not changed, the driver will complain if you load a document from the collection that has additional properties that cannot be mapped. This safe-guards against wreaking havoc in unexpected schemas.

You can change this behavior in several ways:

• You can opt to ignore extra elements by using [BsonIgnoreExtraElements]. This bears the risk that you might loose data if you do a full replace on the document. In this case working with fine-grained updates as opposed to full-document-replacements is key in order to preserve the data that the application does not know about.
• You can add a Dictionary<string, object> to your collection and mark it with \[BsonExtraElements\]. This dictionary will hold all the unmapped properties. When the document is serialized again, the order may change.

If your application is the only one that works with the data, option 1 works well and also configures the application to be tolerant against minor changes in the documents (e.g. adding a field).