ASP.net - Uploading Files Associated with a Database Record? - file-upload

Question

I know that there are tons of examples of multi-part form data uploading in ASP.net. However, all of them just upload files to the server, and use System.IO to write it to server disk space. Also, the client side implementations seem to handle files only in uploading, so I can't really use existing upload plugins.
What if I have an existing record and I want to upload images and associate them with the record? Would I need to write database access code in the upload (Api) function, and if so, how do I pass that record's PK with the upload request? Do I instead upload the files in that one request, obtain the file names generated by the server, and then make separate API calls to associate the files with the record?
While at it, does anyone know how YouTube uploading works? From a user's perspective, it seems like we can upload a video, and while uploading, we can set title, description, tags, etc, and even save the record. Is a record for the video immediately created before the API request to upload, which is why we can save info even before upload completes?
Again, I'm not asking HOW to upload files. I'm asking how to associate uploaded files with an existing record and the API calls involved in it. Also, I am asking for what API calls to make WHEN in the user experience when they also input information about what they're uploading.

Answer 1

I'm assuming you're using an api call to get the initial data for displaying a list of files or an individual file. You would have to do this in order to pass the id back to the PUT method to update the file.
Here's a sample of the GET method:
[HttpGet]
public IEnumerable<FileMetaData> Get()
{
var allFiles = MyEntities.Files.Select(f => new FileMetaData()
{
Name = f.Name,
FileName = f.FileName,
Description = f.Description,
FileId = f.Id,
ContentType = f.ContentType,
Tags = f.Tags,
NumberOfKB = f.NumberOfKB
});
return allFiles;
}
Here's a sample of the POST method, which you can adapt to be a PUT (update) instead:
[HttpPost]
[ValidateMimeMultipartContentFilter]
public async Task<IHttpActionResult> PutFile()
{
try
{
var streamProvider =
await Request.Content.ReadAsMultipartAsync(new InMemoryMultipartFormDataStreamProvider());
//We only allow one file
var thisFile = files[0];
//For a PUT version, you would grab the file from the database based on the id included in the form data, instead of creating a new file
var file = new File()
{
FileName = thisFile.FileName,
ContentType = thisFile.ContentType,
NumberOfKB = thisFile.ContentLength
};
//This is the file metadata that your client would pass in as formData on the PUT / POST.
var formData = streamProvider.FormData;
if (formData != null && formData.Count > 0)
{
file.Id = formData["id"];
file.Description = formData["description"];
file.Name = formData["name"] ?? string.Empty;
file.Tags = formData["tags"];
}
file.Resource = thisFile.Data;
//For your PUT, change this to an update.
MyEntities.Entry(file).State = EntityState.Detached;
MyEntities.Files.Add(file);
await MyEntities.SaveChangesAsync();
//return the ID
return Ok(file.Id.ToString());
}
I got the InMemoryMultipartFormDataStreamProvider from this article:
https://conficient.wordpress.com/2013/07/22/async-file-uploads-with-mvc-webapi-and-bootstrap/
And adapted it to fit my needs for the form data I was returning.