How to define default values or accept empty html input controls in ASP.NET Core method

Question

I have a form with a bunch of controls, but not everyone is required to fill in, so I get an error when I receive the form because some values are not present. I've tried to define default values on the function, but I think it's the [FromForm] that is causing the error.

<table>
    <tr>
        <td>&nbsp;</td>
        <td><input type="text" id="AddressLine1" name="AddressLine1" class="txt-antan address-line" onkeyup="verifyInput()" onchange="verifyInput()" /></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
        <td><input type="text" id="AddressLine2" name="AddressLine2" class="txt-antan address-line" onkeyup="verifyInput()" onchange="verifyInput()" /></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
        <td><input type="text" id="AddressLine3" name="AddressLine3" class="txt-antan address-line" onkeyup="verifyInput()" onchange="verifyInput()" value="-" /></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
        <td><input type="text" id="AddressLine4" name="AddressLine4" class="txt-antan address-line" onkeyup="verifyInput()" onchange="verifyInput()" value="-" /></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
        <td><input type="text" id="AddressLine5" name="AddressLine5" class="txt-antan address-line" onkeyup="verifyInput()" onchange="verifyInput()" placeholder="@_local["WordAddresss"]" /></td>
    </tr>
</table>

AddressLine 3 to 5 are not required and may be empty.

[HttpPost("API/SetCartIdentity")]
public async Task<IActionResult> SetCartIdentityAsync([FromForm(Name = "AddressLine1")] string addressLine1, [FromForm(Name = "AddressLine2")] string addressLine2, [FromForm(Name = "AddressLine3")] string addressLine3, [FromForm(Name = "AddressLine4")] string addressLine4, [FromForm(Name = "AddressLine5")] string addressLine5 = "default value")
{
    return RedirectToActionPermanent("Checkout", "Cart");
}

It will cause an error if any of the input's are empty.

Answer 1

I would suggest creating a class for your input model similar to this:

using System.ComponentModel.DataAnnotations;

    namespace MySample
    {
        public class InputModel
        {
            [Required]
            public string AddressLine1 { get; set; }
            [Required]
            public string AddressLine2 { get; set; }
            public string AddressLine3 { get; set; }
            public string AddressLine4 { get; set; }
            public string AddressLine5 { get; set; } = "default value";
        }
    }

Then, your method signature would look like this:

[HttpPost("API/SetCartIdentity")]
public async Task<IActionResult> SetCartIdentityAsync(InputModel model)
{
    return RedirectToActionPermanent("Checkout", "Cart");
}

You could then also review the form tag helpers available: https://docs.microsoft.com/en-us/aspnet/core/mvc/views/working-with-forms?view=aspnetcore-6.0#the-input-tag-helper

And the validation components here: https://docs.microsoft.com/en-us/aspnet/core/tutorials/first-mvc-app/validation?view=aspnetcore-6.0