How to ignore a specific field when updating db entity?

Question

I have a class MessageModel, which has a field public string? AttachedFile

My controller adds a message to the database

[SwaggerOperation(Summary = "Create Message")]        
public async Task<IActionResult> AddMessage(MessageModel messageModel)
{
    if (messageModel.AttachedFile != null)
    {
        var mediaDto = _mapper.Map<MediaDto>(messageModel);
        var createdMedia = await _mediaService.Create(mediaDto);

        messageModel.SetMediaGuid(createdMedia);
    }
    return Ok(await _messageService.Create(_mapper.Map<MessageDto>(messageModel)));
} 

My other controller edits the message, but i don't want to update AttachedFile field when editing my existing message

[HttpPost]
[SwaggerOperation(Summary = "Edit Message")]

public async Task<IActionResult> EditMessage(MessageModel messageModel)
{
    await _messageService.Update(messageModel.Id, _mapper.Map<MessageDto>(messageModel));
    return Ok();
}

How do i ignore AttachedFile field when using Edit Message Controller

Answer 1

Possibly the easiest option would be to just use 2 separate models (possibly with some base one to contain base/shared props):

public abstract class MessageModelBase
{
   // ...
}

public class AddMessageModel : MessageModelBase
{
   public ... AttachedFile {get; set;}
}

public class EditMessageModel : MessageModelBase
{
}

And use them:

[SwaggerOperation(Summary = "Create Message")]        
public async Task<IActionResult> AddMessage(AddMessageModel messageModel)
{
    // ...
} 

[SwaggerOperation(Summary = "Edit Message")]
public async Task<IActionResult> EditMessage(EditMessageModel messageModel)
{
    // ...
}

Also possibly EditMessage should be PUT, not POST.