MVC3, multiple file upload, model binding - asp.net-mvc-3

Question

There is a view to update a complex model(Transaction).
Complex model has properties which can have multiple attachments(files),
so that user can upload multiple files simultaneously in this form,
and I am trying to save these files to the database.
I have successfully posted multiple files to the server,
following blog post
http://haacked.com/archive/2010/07/16/uploading-files-with-aspnetmvc.aspx.
However in order to save these files, so that I can keep track of which files belongs to which object of the complex model(Transaction) and therefore show them later at appropriate places, I need some way to associate file uploaded to the object it belongs to, but since all files come under name 'files' I don't know how I can make this work.
Here is simplified complex model:
public class Transaction
{
[Key]
public int Id { get; set; }
public virtual PurchaseRequisition PurchaseRequisition { get; set; }
public virtual Evaluation Evaluation { get; set; }
}
Properties of complex model:
public class PurchaseRequisition
{
[Key, ForeignKey("Transaction")]
public int TransactionId { get; set; }
public virtual Transaction Transaction { get; set; }
[Display(Name = "Specifications/Requisitioner's Notes")]
public virtual ICollection<Attachment> SpecsRequisitionerNotesFiles { get; set; }
}
public class Evaluation
{
[Key, ForeignKey("Transaction")]
public int TransactionId { get; set; }
public virtual Transaction Transaction { get; set; }
public virtual ICollection<Attachment> BidResultsFiles { get; set; }
}
public abstract class Attachment
{
[Key]
public int Id { get; set; }
public string FileName { get; set; }
public string FileExtension { get; set; }
public byte[] Data { get; set; }
public Boolean Deleted { get; set; }
}
Here is the controller:
[HttpPost]
public ActionResult Create(TransactionViewModel model, IEnumerable<HttpPostedFileBase> files)
{ //save to database }

Answer 1

Create separate sections in the view for the purchase requisitions and bid results. Something like this:
<form action="" method="post" enctype="multipart/form-data">
<h3>Purchase Requistions</h3>
<label for="file1">Filename:</label>
<input type="file" name="purchasereqs" id="file1" />
<label for="file2">Filename:</label>
<input type="file" name="purchasereqs" id="file2" />
<h3>Bid Results</h3>
<label for="file3">Filename:</label>
<input type="file" name="bidresults" id="file3" />
<label for="file4">Filename:</label>
<input type="file" name="bidresults" id="file4" />
<input type="submit" />
</form>
Then you would have an action signature like this:
[HttpPost]
public ActionResult Create(
TransactionViewModel model,
IEnumerable<HttpPostedFileBase> purchasereqs,
IEnumerable<HttpPostedFileBase> bidresults)
{
//save to database
}