Question

Lets say my c# model updated while correspondent collection still contains old documents, I want old and new documents to coexist in the collection, while using only new version of c# model to read them. I wish no inheritance is used if possible. So I wonder which of this issues are solvable and how:

• there is a new property in c# model which does not present in database. I think it never should be an issue, Mongo knows nothing about it, and it will be initialized with default value. The only issue here is to initialize it with particular value for all old documents, anybody knows how?

• one of property has gone from model. I want MongoDb to find out there is no more property in c# class to map the field of old document to, and to ignore it instead of crashing. This scenario probably sounds a bit strange as it would mean some garbage left in database, but anyway, is the behavior possible to implement/configure?

• type if changed, new type is convertible to old one, like integer->string. Is there any way to configure mapping for old docs?

I can consider using inheritance for second case if it is not solvable otherwise

Answer 1

Most of the answers to your questions are found here.

• BsonDefaultValue("abc") attribute on properties to handle values not present in the database, and to give them a default value upon deserialization
• BsonIgnoreExtraElements attribute on the class to ignore extra elements found during deserialization (to avoid the exception)
• A custom serializer is required to handle if the type of a member is changed, or you need to write an upgrade script to fix the data. It would probably be easier to leave the int on load, and save to a string as needed. (That will mean that you’ll need a new property name for the string version of the property.)