ASP.NET Core: asp-* attributes use request payload over model?

Question

It seems that in ASP.NET Core, the value in asp-* attributes (e.g. asp-for) is taken from the request payload before the model. Example:

P

Answer 1

I can confirm your observation. What's really going to blow your mind is that this:

[HttpPost]
public IActionResult Foo (MyModel m)
{
    m.MyProperty = "changed";
    var result = new MyModel { MyProperty = "changed" };
    return View(result);
}

...gives you the same result.

I think you should log a bug: https://github.com/aspnet/mvc/issues

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Edit: I now remember this issue from previous encounters myself and concede that it isn't necessarily a bug, but rather an unintended consequence. The reasons for the result of executing this code is not obvious. There likely isn't a non-trivial way to surface a warning about this, but PRG is a good pattern to follow.