ModelState.IsValid is always false for RegularExpression ValidationAttribute in MVC 4 - regex

Question

In my class, I have a property for a file attachment like so...
public class Certificate {
[Required]
// TODO: Wow looks like there's a problem with using regex in MVC 4, this does not work!
[RegularExpression(#"^.*\.(xlsx|xls|XLSX|XLS)$", ErrorMessage = "Only Excel files (*.xls, *.xlsx) files are accepted")]
public string AttachmentTrace { get; set; }
}
I don't see anything wrong with my regex, but I always get ModelState.IsValid false. This seems pretty trivial and simple regex, am I missing something? Do I need to write my own custom validation?
I'm populating AttachmentTrace via a regular input of type file:
<div class="editor-label">
#Html.LabelFor(model => model.AttachmentTrace)
</div>
<div class="editor-field">
#Html.TextBoxFor(model => model.AttachmentTrace, new { type = "file" })
#Html.ValidationMessageFor(model => model.AttachmentTrace)
</div>
The action method is just a regular action:
public ActionResult Create(Certificate certificate, HttpPostedFileBase attachmentTrace, HttpPostedFileBase attachmentEmail)
{
if (ModelState.IsValid)
{
// code ...
}
return View(certificate);
}

Answer 1

Ok, here's the solution I found. I'm sure there are other solutions out there. First a little background, because my application uses EF code-first migration, specifying a HttpPostedFileBase property type in my model, produces this error when adding migration:
One or more validation errors were detected during model generation:
System.Data.Entity.Edm.EdmEntityType: : EntityType
'HttpPostedFileBase' has no key defined. Define the key for this
EntityType. \tSystem.Data.Entity.Edm.EdmEntitySet: EntityType:
EntitySet 'HttpPostedFileBases' is based on type 'HttpPostedFileBase'
that has no keys defined.
So I really had to stick with using a string type for the AttachmentTrace property.
The solution is to employ a ViewModel class like this:
public class CertificateViewModel {
// .. other properties
[Required]
[FileTypes("xls,xlsx")]
public HttpPostedFileBase AttachmentTrace { get; set; }
}
Then create a FileTypesAttribute like so, I borrowed this code from this excellent post.
public class FileTypesAttribute : ValidationAttribute {
private readonly List<string> _types;
public FileTypesAttribute(string types) {
_types = types.Split(',').ToList();
}
public override bool IsValid(object value) {
if (value == null) return true;
var postedFile = value as HttpPostedFileBase;
var fileExt = System.IO.Path.GetExtension(postedFile.FileName).Substring(1);
return _types.Contains(fileExt, StringComparer.OrdinalIgnoreCase);
}
public override string FormatErrorMessage(string name) {
return string.Format("Invalid file type. Only {0} are supported.", String.Join(", ", _types));
}
}
In the controller Action, I needed to make a change to use the ViewModel instead, then map it back to my Entity using AutoMapper (which is excellent by the way):
public ActionResult Create(CertificateViewModel certificate, HttpPostedFileBase attachmentTrace, HttpPostedFileBase attachmentEmail) {
if (ModelState.IsValid) {
// Let's use AutoMapper to map the ViewModel back to our Certificate Entity
// We also need to create a converter for type HttpPostedFileBase -> string
Mapper.CreateMap<HttpPostedFileBase, string>().ConvertUsing(new HttpPostedFileBaseTypeConverter());
Mapper.CreateMap<CreateCertificateViewModel, Certificate>();
Certificate myCert = Mapper.Map<CreateCertificateViewModel, Certificate>(certificate);
// other code ...
}
return View(myCert);
}
For the AutoMapper, I created my own TypeConverter for the HttpPostedFileBase as follows:
public class HttpPostedFileBaseTypeConverter : ITypeConverter<HttpPostedFileBase, string> {
public string Convert(ResolutionContext context) {
var fileBase = context.SourceValue as HttpPostedFileBase;
if (fileBase != null) {
return fileBase.FileName;
}
return null;
}
}
That's it. Hope this helps out others who may have this same issue.