New file

public class AppService : IAppService
{
    #region DOK: ADD THIS TO THE DOCUMENTATION

    private readonly ApplicationDbContext _context;
    public AppService(ApplicationDbContext context)
    {
        _context = context;
    }
    #endregion

    public string CheckDirectory(string path)
    {

        if (string.IsNullOrWhiteSpace(path))
        {
            return "Ungültiger Pfad. Bitte geben Sie einen gültigen Pfad ein.";
        }

        if (!System.IO.Directory.Exists(path))
        {
            return "Das angegebene Verzeichnis existiert nicht. Bitte geben Sie einen gültigen Pfad ein.";
        }

        return "Pfad ist sauber, wir fahren fort";
    }


    public DirectoryEntry ScanDirectory(string path, DirectoryEntry? directoryEntry = null)
    {
        try
        {
            var directoryInfo = new DirectoryInfo(path);


            var directoryEntity = new DirectoryEntry
            {
                Path = path,
                FileCount = directoryInfo.GetFiles().Length,
                Size = directoryInfo.GetFiles().Sum(f => f.Length),
                Parent = directoryEntry,//default should be null only if called in the recursion
                SubDirectories = new List<DirectoryEntry>()
            };


            //for all subdirectories
            foreach (var subDirectory in directoryInfo.GetDirectories())
            {
                if (ScanDirectory(subDirectory.FullName, directoryEntity) is DirectoryEntry subDirectoryEntity)
                {
                    directoryEntity.SubDirectories.Add(subDirectoryEntity);
                }
            }
            return directoryEntity;

        }
        catch (UnauthorizedAccessException)
        {
            Console.WriteLine($"Keine berechtigung auf {path}", "es wird übersprungen");
            return null;
        }
    }

    public DirectoryIndex SaveDirectory(DirectoryEntry directoryEntity)
    {

        DirectoryIndex x = new DirectoryIndex();
        x.PathName = directoryEntity.Path;
        _context.DirectoryIndices.Add(x);
        _context.SaveChanges();
        //save to have id



        UpdateIndexId(directoryEntity, x.Id);


        //save again
        _context.DirectoryEntries.Add(directoryEntity);
        _context.SaveChanges();

        return x;
    }


    public void UpdateIndexId(DirectoryEntry directoryEntity, int newId)
    {
        Console.WriteLine($"{directoryEntity.Path}");
        directoryEntity.IndexId = newId;

        foreach (var subDirectory in directoryEntity.SubDirectories)
        {
            UpdateIndexId(subDirectory, newId);
        }
    }

    public IEnumerable<DirectoryEntry> GetDirectoriesEntrie()
        {
        //remove include to test
        return _context.DirectoryEntries.Include(z => z.SubDirectories);
        }
}

    public class DirectoryEntry
    {
        public int Id { get; set; }  
        public string Path { get; set; }  
        public int FileCount { get; set; }  
        public long Size { get; set; }  
        public int? ParentId { get; set; }  
        public DirectoryEntry Parent { get; set; } 
        public int IndexId { get; set; }
        public ICollection<DirectoryEntry> SubDirectories { get; set; } = new List<DirectoryEntry>();  // Collection of Subdirectories...
    }

    public class DirectoryIndex
    {
        public int Id { get; set; }
        public DateTime Index { get; set; } = DateTime.Now;
        public string PathName { get; set; }
}

@page "/"
@using RecursiveDirectoryWeb.Data.AppService
@using RecursiveDirectoryWeb.Models
@rendermode InteractiveServer
@using Microsoft.AspNetCore.Components.QuickGrid;

<PageTitle>Verzeichnisanalyse</PageTitle>

@inject IAppService appService

<p>
    <label>Pfad eingeben: <input @bind="inputValue" /></label>
</p>

<p>You entered: @inputValue</p>
@* Quickgrid later *@

@if (inputValue != null)
{
    checkresult = appService.CheckDirectory(inputValue);
    <p> @checkresult</p>
    {
        entry = appService.ScanDirectory(inputValue);
    }

    <button @onclick="() => StoretoDb() ">
        Push to Db !
    </button>


    @if (itemsQueryable != null)
    {
        <QuickGrid Items="@itemsQueryable" Pagination="pagination"> 
          <PropertyColumn Property="x => x.Size" Title="Größe" Sortable="true">
    </PropertyColumn> 
    <PropertyColumn Property="x => x.Path" Title="Name" Sortable="true">
    </PropertyColumn>
            <PropertyColumn Property="x => x.ParentId" Title="Name" Sortable="true">
            </PropertyColumn>
        </QuickGrid>
        <Paginator State="@pagination" />
    }
}

@code {
    //sets how many items per Grid-Page
    public PaginationState pagination = new PaginationState { ItemsPerPage = 10 };
    private string inputValue;
    public string checkresult;
    public DirectoryEntry entry;
    IQueryable<DirectoryEntry>? itemsQueryable;

    public void StoretoDb()
    {
        var item = appService.SaveDirectory(entry);
        //after thats finished load data

        //load DAta to GRID and get LOST!
        itemsQueryable = appService.GetDirectoriesEntrie().ToList().AsQueryable().Where(x => x.IndexId == item.Id);
    }
}