C# Mongodb Driver - How to insert an element into an array at position 0

Question

I cannot seem to find a way to insert element at specific index in an array in the Mongodb C# Driver. - For example insert an element at position 0.

The only obvious insert into the array is using the push but that is appending to the end of the array.

I have tried the following but does not work.

var filter = Builders<ChatRoom>.Filter.Eq(Keys.MongoId, ObjectId.Parse(chatRoomId));
var update = Builders<ChatRoom>.Update.Set(Keys.Comments + ".$.-1", comment);

or

var update = Builders<ChatRoom>.Update.Push(Keys.Comments+".-1",comment);

But it doesn't work. Also I cannot seem to find the $position operator in the Mongodb C# docs. - was hoping that could help, if it was relevant.

jonprasetyo · Accepted Answer · 2015-09-12 15:44:32Z

4

Okay super easy, after exploring around the driver and the help of intellisense from Visual Studio here is the correct answer:

var filter = Builders<ChatRoom>.Filter.Eq(Keys.MongoId, ObjectId.Parse(chatRoomId));
var update = Builders<ChatRoom>.Update.PushEach(Keys.Comments, new List<Comment>() { comment }, position: 0);
await MongoCollections.GetChatRoomCollection().UpdateOneAsync(filter, update);

answered Sep 12, 2015 at 15:44

jonprasetyo

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3 Comments

Craig Wilson Over a year ago

Sometimes, it's best to try and figure out how mongodb supports this before attempting it in the driver: docs.mongodb.org/manual/reference/operator/update/push

jonprasetyo Over a year ago

@CraigWilson Thanks for your comment, you must be the guy who created the Driver, nice to meet you. Yes I agree, I actually knew mongodb supports it as i have written it once in Python. I just didn't know how it was done in C#.

Woody1193 Over a year ago

@CraigWilson Sorry, but what is the time complexity of this operation? I assume O(n) but I'd like clarification if you please

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