updateChatPartitions.txt

exports = async function(currentUserId, friendUserId) {
  
  const mongodb = context.services.get("mongodb-atlas");
  const users = mongodb.db("CustomUserDB").collection("CustomUserData");
  let user = await users.findOne({userId: currentUserId});
  let friendUser = await users.findOne({userId: friendUserId});
  
  var chatPartition = currentUserId + "_" + friendUserId;
  if (currentUserId > friendUserId) {
      chatPartition = friendUserId + "_" + currentUserId;
  }
        
  var userChatPartitions = { "$push": {
      "chatPartitions": chatPartition
      }
  };       
  users.updateOne({_id: user._id}, userChatPartitions, {upsert: false});      

  var friendUserChatPartitions = { "$push": {
      "chatPartitions" : chatPartition
      }
  };
  users.updateOne({_id: friendUser._id}, friendUserChatPartitions, {upsert: false});
  
  return chatPartition;
};