Hello,
I'm trying to understand what I did wrong in the example of data files that uMod provide (https://umod.org/documentation/api/data-files).
From what I understand, if I'm already in the data file, it only reply a message else it add me to the file. But it's not working, it add me to the file everytime I run the command...
Can you help me?

using Oxide.Core;
using Oxide.Core.Libraries.Covalence;
using System.Collections.Generic;

namespace Oxide.Plugins
{
    [Info("Plugin Name", "Author", "1.0.0")]
    [Description("Description of the plugin.")]
    class PluginName : CovalencePlugin
    {
        private StoredData storedData;

        private class StoredData
        {
            public HashSet<PlayerInfo> Players = new HashSet<PlayerInfo>();

            public StoredData()
            {
            }
        }

        private void Init()
        {
            storedData = Interface.Oxide.DataFileSystem.ReadObject<StoredData>("MyDataFile");
        }

        void Loaded()
        {
            Puts("Loaded works!");
        }

        private class PlayerInfo
        {
            public string Id;
            public string Name;

            public PlayerInfo()
            {
            }

            public PlayerInfo(IPlayer player)
            {
                Id = player.Id;
                Name = player.Name;
            }
        }

        [Command("test")]
        private void TestCommand(IPlayer player, string command, string[] args)
        {
            PlayerInfo info = new PlayerInfo(player);
            if (storedData.Players.Contains(info))
            {
                player.Reply("Your data has already been added to the file");
            }
            else
            {
                storedData.Players.Add(info);
                player.Reply("Saving your data to the file...");
                Interface.Oxide.DataFileSystem.WriteObject("MyDataFile", storedData);
            }
        }
    }
}​

Because PlayerInfo is always unique and it is a class, you create a new one every time. Instead you should check if there is one with the same user ID.