ASP.NET Core MVC 文件上傳下載完整實戰教程：從表單到數據庫存儲

核心差異：WebForms vs MVC

一、文件上傳完整實現

1. View 頁面 (Razor)

@model FileUploadViewModel


    

        
        
        
    
    

        
        
    
    上傳




    
    批量上傳

2. ViewModel 與驗證

public class FileUploadViewModel
{
    [Required(ErrorMessage = "請選擇文件")]
    [DataType(DataType.Upload)]
    [MaxFileSize(10 * 1024 * 1024)] // 自定義驗證特性 10MB
    [AllowedExtensions(new[] { ".jpg", ".png", ".pdf", ".docx" })]
    public IFormFile File { get; set; }
    
    [StringLength(500)]
    public string Description { get; set; }
}

public class MaxFileSizeAttribute : ValidationAttribute
{
    private readonly long _maxBytes;
    public MaxFileSizeAttribute(long maxBytes) => _maxBytes = maxBytes;
    
    protected override ValidationResult IsValid(object value, ValidationContext context)
    {
        if (value is IFormFile file && file.Length > _maxBytes)
            return new ValidationResult($"文件大小不能超過 {_maxBytes / 1024 / 1024}MB");
        return ValidationResult.Success;
    }
}

3. Controller 處理邏輯

[HttpPost]
[ValidateAntiForgeryToken]
public async Task Upload(FileUploadViewModel model)
{
    if (!ModelState.IsValid) return View(model);
    
    // 1. 生成安全文件名
    string originalName = Path.GetFileName(model.File.FileName);
    string safeName = $"{Guid.NewGuid()}{Path.GetExtension(originalName)}";
    
    // 2. 確定存儲路徑
    string uploadsFolder = Path.Combine(_env.WebRootPath, "uploads", "files");
    Directory.CreateDirectory(uploadsFolder);
    string filePath = Path.Combine(uploadsFolder, safeName);
    
    // 3. 保存文件 (異步流複製)
    using (var stream = new FileStream(filePath, FileMode.Create))
    {
        await model.File.CopyToAsync(stream);
    }
    
    // 4. 可選：存入數據庫記錄
    var fileRecord = new FileRecord
    {
        OriginalName = originalName,
        StoredName = safeName,
        ContentType = model.File.ContentType,
        Size = model.File.Length,
        Description = model.Description,
        UploadTime = DateTime.UtcNow,
        UploadedBy = User.Identity.Name
    };
    _context.FileRecords.Add(fileRecord);
    await _context.SaveChangesAsync();
    
    TempData["Success"] = "上傳成功";
    return RedirectToAction("Index");
}

// 多文件上傳
[HttpPost]
public async Task UploadMultiple(List files)
{
    var results = new List