How to test that a string field in a MongoDB document is not empty?

Question

I am trying to get the number of documents that have a field with an empty string. This field, lets call it "Field_One" is present in all documents (so, to be clear, I am not trying to find if the field exists or not, I want to find which documents have nothing (empty string) in field "Field_One".

I tried using (using the C# driver):

collection.Find(Query.NE("Field_One", BsonNull.Value)).Count()
collection.Find(Query.NE("Field_One", BsonString.Null)).Count()

and even (someone suggested this somewhere):

collection.Find(Query.GT("Field_One", BsonString.Empty)).Count()

But it doesn't work (they return all the documents).

Also, as a related question: Is this the best way to get the number of matching documents in a collection? As far as I understand this, it wont actually retrieve the documents from the database to my program, so the count calculation is done in the MongoDB server.

Answer 1

BsonNull.Value translates into null
BsonString.Empty translates into ""
BsonObject.Create("") translates into "" as well

 collection.Find(Query.NE("Field_One", BsonString.Empty)).Count()

translates into "Field_One": { "$ne": "" } what should be exactly what you are looking for if the field is actually filled with ""