Insert new record to array on object on a record MongoDB C#

Question

I have a table to store users with records like this.

{
    "_id" : "",
    "Username" : "",
    "Points" : 0,
    "CompletedAchievements" : {
        "Public": [], 
        "Private": []
    },
    "ActiveAchievements" : {
        "Public": [], 
        "Private": []
    },
    "Kudos" : [],
    "Teams" : [],
    "UserType" : "Admin",
    "PrivateAchievements": []
}

My C# code

public void Add<T>(string userId, string achievementId, int progress) {
        var collection = this.db.GetCollection<T>(typeof(T).Name);

        var filter = Builders<T>.Filter.And(
             Builders<T>.Filter.Eq("_id", userId),
             Builders<T>.Filter.Eq("ActiveAchievements.Public", "Public"));

        var update = Builders<T>.Update.Push("ActiveAchievements.$.Public", new 
        ActiveAchievement() { _id = achievementId, Progress = progress });

            collection.FindOneAndUpdateAsync(filter, update);
        }

I am trying to add a value to the Public Array in active achievements. Does anyone know why this isn't working?

Answer 1

Was a simple fix in the end. Only 1 filter required the _id filter to get the record.

var filter = Builders<T>Filter.Eq("_id", userId);

Once I had that I could do the following update onto the array on the object.

var update = Builders<T>.Update.Push("ActiveAchievements.Public", new 
        ActiveAchievement() { _id = achievementId, Progress = progress });