Simple scenario here:

Trying to do a simple find on a field that is set to "IgnoreIfDefault", and thus is not a field in the document if the value is the default. However, this causes problems with querying...

Collection.Find(d => d.ActiveState == ActiveStateType.Active).ToListAsync().Result

With this class:

public class JebsClass {
     [BsonIgnoreIfDefault]
     [BsonDefaultValue(ActiveStateType.Active)]
     public ActiveStateType ActiveState { get; set; }
     public int Field1 {get; set; }
}

This finds records like this

{
     Field1: 5,
     ActiveState: "Active"
}

but NOT documents like this

{
     Field1: 5
}

It seems to me that the Find interface methods should take into account Default values, and update the translated query to include a $exists: false for ActiveState.