Select all _id from mongodb collection with c# driver

Question

I have large document collection in mongodb and want to get only _id list. Mongodb query is db.getCollection('Documents').find({},{_id : 0, _id: 1}). But in C# query

IMongoCollection<T> Collection { get; set; }

...

List<BsonDocument> mongoResult = this.Collection.FindAsync(FilterDefinition<T>.Empty, new FindOptions<T, BsonDocument>() { Projection = "{ _id: 0, _id: 1 }" }).Result.ToList();

throw exeption InvalidOperationException: Duplicate element name '_id'. I want to get only _id list, other fileds not needed. Documents may have different structures and exclude all other fileds manualy difficult.

What C# query corresponds to the specified mongodb query db.getCollection('Documents').find({},{_id : 0, _id: 1}?

UPDATE: Do not offer solutions related query large amounts of data from the server, for example like

this.Collection.Find(d => true).Project(d => d.Id).ToListAsync().Result;

Answer 1

Since your using C# driver I would recommend to use the AsQueryable and then use linq instead.

In my opinion it is better since you wouldn't need the magic strings and you would benefit from your linq knowledge. Then it would look something like this

database.GetCollection<T>("collectionname").AsQueryable().Select(x => x.Id);