How to prevent inserting null value in Image field when the record is modified and saved using MVC4? - asp.net-mvc-4

Question

I am storing image in Database successfully.
I want to display this image in Edit form to modify and save changes. But I'm just able to display image in Edit form my code for modifying and save images in data base is not working it's inserting null values in Image field when the record is modified and saved or if I modify all other fields in Edit view excepting image field.
Would someone please tell me what mistake I'm doing? Here is my controller action:
public ActionResult Edit(student st) {
if (ModelState.IsValid) {
var imgFile = Request.Files["imgFile"];
if (imgFile != null && imgFile.ContentLength > 0) {
var fileName = Path.GetFileName(imgFile.FileName);
var path = Path.Combine(Server.MapPath("~/Content/stImgs"), fileName);
imgFile.SaveAs(path);
st.Img = fileName;
}
}
try {
db.Entry(st).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("student");
} catch {
return View(st);
}
}
Here is view:
<img src="/Content/Imgs/#Model.Img">
</div>
<label for="file">Image:</label>
<input type="file" name="file" id="file" />
#Html.ValidationMessageFor(item => item.file)

Answer 1

try adding a HttpPostedFileBase parameter in your action method:
public ActionResult Edit(student st, HttpPostedFileBase file)
{
if (ModelState.IsValid) {
if (file != null && file.ContentLength > 0) {
var fileName = Path.GetFileName(file.FileName);
var path = Path.Combine(Server.MapPath("~/Content/stImgs"), fileName);
file.SaveAs(path);
st.Img = fileName;
}
}
try {
db.Entry(st).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("student");
} catch {
return View(st);
}
}
Make sure the parameter's name is the same as the file's name in the form!
Also, make sure your Form is set to enctype multipart/form-data:
Html.BeginForm(
action, controller, FormMethod.Post, new { enctype="multipart/form-data"})

Answer 2

Microsoft change how update action method work.
please read section "Update the Edit HttpPost Method " from the following link.
These changes implement a security best practice to prevent overposting, The scaffolder generated a Bind attribute and added the entity created by the model binder to the entity set with a Modified flag. That code is no longer recommended because the Bind attribute clears out any pre-existing data in fields not listed in the Include parameter. In the future, the MVC controller scaffolder will be updated so that it doesn't generate Bind attributes for Edit methods.
The new code reads the existing entity and calls TryUpdateModel to update fields from user input in the posted form data. The Entity Framework's automatic change tracking sets the Modified flag on the entity. When the SaveChanges method is called, the Modified flag causes the Entity Framework to create SQL statements to update the database row. Concurrency conflicts are ignored, and all columns of the database row are updated, including those that the user didn't change. (A later tutorial shows how to handle concurrency conflicts, and if you only want individual fields to be updated in the database, you can set the entity to Unchanged and set individual fields to Modified.)