Why do I get null instead of empty string when receiving POST request in from Razor View?

I used to receive empty string when there was no value:

[HttpPost]
public ActionResult Add(string text)
{
// text is "" when there's no value provided by user
}

But now I'm passing a model

[HttpPost]
public ActionResult Add(SomeModel Model)
{
// model.Text is null when there's no value provided by user
}

So I have to use the ?? "" operator.

Why is this happening?

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I am trying this in Create and Edit (my object is called 'entity'):-

        if (ModelState.IsValid)
{
RemoveStringNull(entity);
db.Entity.Add(entity);
db.SaveChanges();
return RedirectToAction("Index");
}


return View(entity);
}

Which calls this:-

    private void RemoveStringNull(object entity)
{
Type type = entity.GetType();
FieldInfo[] fieldInfos = type.GetFields(BindingFlags.Instance | BindingFlags.GetField | BindingFlags.Public | BindingFlags.NonPublic);
for (int j = 0; j < fieldInfos.Length; j++)
{
FieldInfo propertyInfo = fieldInfos[j];
if (propertyInfo.FieldType.Name == "String" )
{
object obj = propertyInfo.GetValue(entity);
if(obj==null)
propertyInfo.SetValue(entity, "");
}
}
}

It will be useful if you use Database First and your Model attributes get wiped out each time, or other solutions fail.

The default model binding will create a new SomeModel for you. The default value for the string type is null since it's a reference type, so it's being set to null.

Is this a use case for the string.IsNullOrEmpty() method?

最佳答案

You can use the DisplayFormat attribute on the property of your model class:

[DisplayFormat(ConvertEmptyStringToNull = false)]