ASP.NET 核心 MVC 为空 object 来自响应

Question

I'm having some trouble with this code, I have used something similar before and is working but it isn't on this one I don't know why. Each time I hit submit the object message comes empty, the only values that are submitted into the database are the ones that I add in the controller like the Date for example, I don't know much about ASP.NET to know why is it failing nor the correct terms to look for myself on google

Model

public class Message {
        [BsonRepresentation(BsonType.ObjectId)]
        public string Id { get; set; }
        [BsonElement("date")]
        public string Date;
        [BsonElement("sender")]
        public string Sender;
        [BsonElement("body")]
        public string Body;
        [BsonElement("type")]
        public string Type;
        [BsonElement("subject")]
        public string Subject;
    }

Controller

[HttpPost]
public IActionResult Write(Message msg) {
    Mongo.Instance.InsertMessage(new Message() {
        Subject = msg.Subject,
        Body = msg.Body,
        Date = DateTime.Now.ToString("dd/MM/yyyy"),
        Type = msg.Type,
        Sender = "None"
    });
    return RedirectToAction("Index", "Home");
}

Form

 @using (Html.BeginForm("Write", "CCG", FormMethod.Post)) {


            <div class="form-group">
                <p>Subject</p>
                @Html.TextBoxFor(model => model.Subject)
            </div>

            <div class="form-group">
                @{
                    List<SelectListItem> items = new List<SelectListItem>();
                    items.Add(new SelectListItem() {
                        Text = "Petition",
                        Value = "petition"
                    });
                    items.Add(new SelectListItem() {
                        Text = "Congratulate",
                        Value = "congratulate"
                    });
                    items.Add(new SelectListItem() {
                        Text = "Offer",
                        Value = "offer"
                    });
                }
                @Html.DropDownListFor(model => model.Type, items)
            </div>

            <div class="form-group">
                <p>Body</p>
                @Html.TextAreaFor(model => model.Body)
            </div>

            <input type="submit" value="Send" />
        }

Answer 1

I'm pretty sure uou need to make those fields into properties by adding get and set methods.

eg

    public class Message {
        [BsonRepresentation(BsonType.ObjectId)]
        public string Id { get; set; }
        [BsonElement("date")]
        public string Date { get; set; }
        [BsonElement("sender")]
        public string Sender { get; set; }
        [BsonElement("body")]
        public string Body { get; set; }
        [BsonElement("type")]
        public string Type { get; set; }
        [BsonElement("subject")]
        public string Subject { get; set; }
    }

Answer 2

When creating a model class for API objects make sure always have the getter and setter. :) Happy Coding

public class Activity
{
    public Guid Id { get; set; }
    public string ActivityName { get; set; }
    public string ActivityDescription { get; set; }
    public string ActivityLink { get; set; }
    public string ActivityVenue { get; set; }
    public bool IsActive { get; set; }
    public DateTime DateCreated { get; set; }
}