ASP.NET MVC Model Mapping from Session - asp.net-mvc

Question

I upload an email through Ajax, parse it and then return some email properties as a partial view. If the user submits the form, the fields go to the post, however at this point I need to also retrieve the original file to store it in the database (so I won't store anything the user uploads, only relevant files). To do this, I store the File Stream (as byte[]) of the email in session. As there might be multiple pages open at the same time I save the emails in session as a list.
I then use the Validate event of the model to extract the byte[] FileStream from Session.
public class EmailModel
{
[Required]
[Display(Name = "TO")]
public string To { get; set; }
[Display(Name = "FROM")]
[Required]
public string From { get; set; }
[Display(Name = "Date")]
public DateTime Data { get; set; }
[Display(Name = "Location of requester")]
public string Location { get; set; }
[Required]
[Display(Name = "Subject of the mail ")]
public string SubjectMail { get; set; }
[Required]
[Display(Name = "Description ")]
public string EmailBodyAsText { get; set; }
public string EmailTypeAsString { get; set; }
public byte[] FileStream { get; set; }
public int ID { get; set; }
public string KendoUniqueId { get; set; }
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
FileStream = ExtractEmailFromSession(KendoUniqueId, HttpContext.Current.Session);
yield return null;
}
private byte[] ExtractEmailFromSession(string emailId, HttpSessionState session)
{
if (!string.IsNullOrEmpty(emailId))
{
var emailList = (List<EmailInSession>)session["emailInSession"];
return emailList.FirstOrDefault(x => x.EmailUniqueId == emailId)?.File;
}
else return null;
}
}
I think this is a bit of smelly code as I retrieve the content from an event that is supposed to be used for validating the data, so I am trying to figure out the proper place to do this. I know I can use IModelBinder to create a custom binder but then I need to bind all the properties which seems overkill for my purpose. Ideally I want to use a custom attribute only for the FileStream property that would extract the data from session and return it to the model. Is there such a possibility?

Answer 1

In case someone else comes to this thread in the future with a similar problem, please have a look below. Please bear in mind I could not make this really generic as this resolves a very specific situation. I created a Model Binder that inherits the default model binder. This allowed me to use the base BindModel method that did most of the job for me (the usual mapping of properties from the context that MVC does for us). Then I went for the specific property that I wanted to populate and extracted the data from the session.
public class SessionModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
try
{
var model = (EmailModel)base.BindModel(controllerContext, bindingContext);
model.FileStream = ExtractEmailFromSession(model.KendoUniqueId, HttpContext.Current.Session);
return model;
}
catch (Exception ex)
{
bindingContext.ModelState.AddModelError("","No data");
return null;
}
}
private byte[] ExtractEmailFromSession(string emailId, HttpSessionState session)
{
if (!string.IsNullOrEmpty(emailId))
{
var emailList = (List<EmailInSession>)session["emailInSession"];
return emailList?.FirstOrDefault(x => x.EmailUniqueId == emailId)?.File;
}
else return null;
}
}
Besides this, the new model binder needed to be registered. This is the place where you need to decide for which models your model binder applies.
public class SessionModelBinderProvider : IModelBinderProvider
{
public IModelBinder GetBinder(Type modelType)
{
if (modelType == typeof(EmailModel))
return new SessionModelBinder();
else return null;
}
}
Lastly, I needed to register my new binder provider so MVC knows about it. This is done by adding the line below in global asax (please note you need to put it in the chain at first position - 0, otherwise default model binder would kick in and yours will never be reached):
ModelBinderProviders.BinderProviders.Insert(0, new SessionModelBinderProvider());