遍歷集合時的實體框架異常

Question

我構建了一個簡單的文件管理器，該文件管理器從兩個表（文件夾和文件）中提取數據。 當您上載文件時，它將被寫入服務器上的磁盤。 當我需要刪除一個文件夾及其所有子文件夾，子文件夾文件和父文件夾文件時，請選擇該文件夾，然后單擊“刪除”，這將執行以下控制器操作。

更新如果我更改對.ToList（）的任何后續調用，它將起作用。

    [HttpPost]
    public JsonResult DeleteFolder(int folderID)
    {
        var repo = new FileManagerRepository();

        var folder     = repo.GetFolder(folderID);
        var subfolders = repo.GetSubFolders(folderID).ToList();
        var files      = repo.GetFiles(folderID).ToList();

        // delete sub-folders
        if (subfolders.Count() != 0)
        {
            foreach (var subfolder in subfolders)
            {
                // delete sub-folder files
                var subfiles = repo.GetFiles(subfolder.folder_id).ToList();
                if (subfiles.Count() != 0)
                {
                    foreach (var file in subfiles)
                    {
                        repo.DeleteFile(file.file_id);
                        System.IO.File.Delete(Server.MapPath("/content/upload/" + file.file_name));
                    }
                }
                repo.DeleteFolder(subfolder.folder_id);
            }
        }
        // delete files
        if (files.Count() != 0)
        {
            foreach (var file in files)
            {
                repo.DeleteFile(file.file_id);
                System.IO.File.Delete(Server.MapPath("/content/upload" + file.file_name));
            }
        }
        // delete the folder            
        if (folder != null)
        {
            repo.DeleteFolder(folder.folder_id);                
        }
        repo.Save();
        return new JsonResult();
    }

現在這里是FileManagerRepository

 public class FileManagerRepository
{
    private readonly iau_idahoEntities db = new iau_idahoEntities();

    public IQueryable<folders> GetParentFolders()
    {
        return db.folders.Where(f => f.parant_folder_id == 0);
    }

    public IQueryable<folders> GetSubFolders()
    {
        return db.folders.Where(f => f.parant_folder_id != 0);
    }
    public IQueryable<folders> GetSubFolders(int folder_id)
    {
        return db.folders.Where(f => f.parant_folder_id != 0 && f.parant_folder_id == folder_id);
    } 


    public IQueryable<Files> GetFiles(int id)
    {
        return db.Files.Where(f => f.folder_id == id);
    }

    public Files GetFile(int id)
    {
        return db.Files.SingleOrDefault(f => f.file_id == id);
    }

    public void UpdateDownloadCount(int id)
    {
        var file = GetFile(id);
        file.downloaded += 1;         
    }
    public void AddFolder(int parentFolderID, string folderName)
    {
        var folder = new folders { create_date = DateTime.Now, parant_folder_id = parentFolderID, folder_name = folderName };
        db.folders.AddObject(folder);
    }

    public void DeleteFolder(int folder_id)
    {
        var folder = db.folders.SingleOrDefault(f => f.folder_id == folder_id);
        db.folders.DeleteObject(folder);
    }
    public void Save()
    {
        db.SaveChanges();
    }

    public void AddFile(int folder_id,string filename, string description)
    {
        var file = new Files { 
            folder_id = folder_id, 
            file_name = filename, 
            file_extension = filename.Substring(filename.Length - 3, 3), 
            description = description,
            downloaded = 0, 
            physical_name = filename.Substring(0, filename.Length - 4), 
            upload_date = DateTime.Now 
        };
        db.Files.AddObject(file);            
    }

    internal void DeleteFile(int fileID)
    {
        var fileToDelete = db.Files.SingleOrDefault(file => file.file_id == fileID);
        db.Files.DeleteObject(fileToDelete);
    }

    internal folders GetFolder(int folderID)
    {
        return db.folders.SingleOrDefault(folder => folder.folder_id == folderID);
    }
}

問題是我不斷收到以下EF異常： 已經有與此命令關聯的打開的DataReader，必須先關閉它

我試圖將MultipleActiveResultSets = true添加到web.config中的連接字符串中，但是仍然出現異常。 我知道為什么會引發該異常，但是我不知道如何做我需要做的事情並防止其引發異常。

請幫忙！！！

Answer 1

更改var subfolders = repo.GetSubFolders(folderID); var subfolders = repo.GetSubFolders(folderID).ToList();

Answer 2

如果我將對存儲庫的所有后續調用都更改為ToList（），則所有工作都應該像它應該的那樣。

    var folder     = repo.GetFolder(folderID);
    var subfolders = repo.GetSubFolders(folderID).ToList();
    var files      = repo.GetFiles(folderID).ToList();

    // delete sub-folders
    if (subfolders.Count() != 0)
    {
        foreach (var subfolder in subfolders)
        {
            // delete sub-folder files
            var subfiles = repo.GetFiles(subfolder.folder_id).ToList();