ASP.NET 内核 - 如何解决“ICollection”<approvalattachment> ' 不包含 'FilePath' 的定义并且没有可访问的扩展方法</approvalattachment>

Question

In ASP.NET Core-6 Web API, I have these models:

public class LeaveApplication
{
    public Guid Id { get; set; }
    public Guid EmployeeId { get; set; }
    public string ReferenceNumber { get; set; }
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
    public virtual Employee Employee { get; set; }
    public virtual LeaveApproval LeaveApproval { get; set; }
}

public class LeaveApproval
{
    public Guid Id { get; set; }
    public bool? IsApproved { get; set; }
    public DateTime? ApprovedDate { get; set; } = null;
    public virtual ICollection<LeaveApprovalAttachment> LeaveApprovalAttachments { get; set; }
}

public class LeaveApprovalAttachment
{
    public Guid Id { get; set; }
    public Guid LeaveApprovalId { get; set; }
    public string FileType { get; set; }
    public string FileName { get; set; }
    public string FilePath { get; set; }
    public long? FileSize { get; set; }
    public virtual LeaveApproval LeaveApproval { get; set; }
}

A LeaveApplication has one LeaveApproval, while a LeaveApproval can have many LeaveApprovalAttachments.

Based on parameter id, I want to get a filepath of a LeaveApprovalAttachment and download the document. So, I have this code:

public async Task<LeaveApplication> GetLeaveDocumentByIdAsync(Guid id)
{
    var leave = await _dbContext.LeaveApplications
                    .Where(m => (bool)m.IsApproved)
                    .Include(x => x.LeaveApproval)
                    .ThenInclude(x => x.LeaveApprovalAttachments)
                    .FirstOrDefaultAsync(x => x.LeaveApproval.LeaveApprovalAttachments.Any(x => x.Id == id));
    var path = Path.Combine(Directory.GetCurrentDirectory(), leave.LeaveApproval.LeaveApprovalAttachments.FilePath);
    var memory = new MemoryStream();
    using (var stream = new FileStream(path, FileMode.Open))
    {
       await stream.CopyToAsync(memory);
    }
    memory.position = 0;
    var contentType = "APPLICATION/octet-stream";
    var fileName = Path.GetFileName(path);
    return File(memory, contentType, fileName);
}

But I got this error:

Error CS1061 'ICollection' does not contain a definition for 'FilePath' and no accessible extension method 'FilePath' accepting a first argument of type 'ICollection' could be found (are you missing a using directive or an assembly reference?)

and it highlights FilePath in leave.LeaveApproval.LeaveApprovalAttachments.FilePath

How do I resolve this?

Thanks

Answer 1

From here:

public virtual ICollection<LeaveApprovalAttachment> LeaveApprovalAttachments { get; set; }

LeaveApprovalAttachments property is a collection. You can't direct access via leave.LeaveApproval.LeaveApprovalAttachments.FilePath .

Instead, you need to provide the index to LeaveApprovalAttachments as:

leave.LeaveApproval.LeaveApprovalAttachments[0].FilePath

Or to get the first item of LeaveApprovalAttachments :

using System.Linq;

var leaveApprovalAttachment = leave.LeaveApproval.LeaveApprovalAttachments.FirstOrDefault();
if (leaveApprovalAttachment != null)
{
    var path = Path.Combine(Directory.GetCurrentDirectory(), leaveApprovalAttachment.FilePath);

    ...
}

Answer 2

You're getting that error because LeaveApprovalAttachments is of type ICollection<LeaveApprovalAttachment> and not LeaveApprovalAttachment . You can see from the documentation of ICollection<T> that there is no FilePath property. You also can't just access a property of the element type, which is LeaveApprovalAttachment in this case, from the ICollection<T> because you have multiple LeaveApprovalAttachment s. How can it know which one you want to access?

Looking at your code, it seems like you only need a single LeaveApprovalAttachment , so the best way to resolve it in this particular case is probably just to select the one LeaveApprovalAttachment that you need, rather than the entire LeaveApplication .

Maybe something like this...

var leaveAttachment = _dbContext
    .LeaveApplications
    .Include(la => la.LeaveApproval)
    .ThenInclude(la => la.LeaveApprovalAttachments)
    .Where(la => (bool)la.IsApproved)
    .SelectMany(la => la.LeaveApproval.LeaveApprovalAttachments)
    .FirstOrDefault(laa => laa.Id == id);    

Note that you're querying on LeaveApplication.IsApproved which doesn't seem to exist on your model, but I tried to replicate your query as much as possible.