我的Razor模型在Post上为空

Question

I have the following Type which I am using to extend another Type that is used throughout our system:

    public class SystemUser : User
    {
        public int? RoleId
        {
            get { return this.Relationhip.FirstOrDefault().TypeList.FirstOrDefault().Id();}
            set { RoleId = value; }
        }

        public Role _Role
        {
            get { return (Role)RoleId; }
            set { RoleId = (int)value; }
        }

        public SelectListItem[] RolesList { get; set; }

        public bool IsA(params Role[] roles)
        {
            return new List<Role>(roles).Any(v => v.Equals(_Role));
        }

        public bool IsNotA(params Role[] roles)
        {
            return !(new List<Role>(roles).Any(v => v.Equals(_Role)));
        }
    }

I'm essentially using this Type to act as a container for data from our database and passing it from a controller to our view as an @model. The view Gets populated just fine, but after I modify the model using @Html.LabelFor() fields, and go to pass that data to a controller that we use to save the updated data to the database, the model is null. If I step through the POST, I get a NullReferenceException on the getter of the ROleId in my SystemUser class. Notice the _Role property; It's known that if a property of a class has the same name as its Type, the model will post empty to the controller, but I've fixed that already.

This is the meat of the View:

@model SystemUser
@using (Html.BeginForm("Usr", "Mr", FormMethod.Post, new {@autocomplete="off"}))
    {
        //Fields removed for sake of simplifying stackoverflow post

        <input class="button green-bg" type="submit" value="Save" />
        <input class="button gray-bg" type="button" onclick="location.href='@Url.Action("View", "Mr")'" value="Cancel" />
    }

Any help here would be greatly appreciated.

Answer 1

While you are populating the model in the controller to create the view, you get an EF model (by the look of your code) including child relationships .

The view will only post back simply properties that match named input elements on the page .

As Relationhip is a server-side collection, that property will be null inside the post action. The post action receives a simple version of the class (foreign key relationships are not populated).

If you need it, inside the controller you need to repopulate that property (eg based on a posted back ID value).

If you show your controller code and the base User class too, I may be able to suggest specific changes to work around this :)

Workaround:

Ensure the getter property tests if the collection is present:

    public int? RoleId
    {
        get { return this.Relationhip == null ? null : this.Relationhip.FirstOrDefault().TypeList.FirstOrDefault().Id();}
        set { RoleId = value; }
    }

Additional:

I am also a little concerned that as there is no field backing the RoleId property so set { RoleId = value; } set { RoleId = value; } is actually a recursive call. You might want to check this.

As it is a derived property I would have expected it to look like this (no setter):

    public int? RoleId
    {
        get { return this.Relationhip.FirstOrDefault().TypeList.FirstOrDefault().Id();}
    }

or, if it is a act as a cached local value for the database, add a private field to back the property with:

    private int? roleId;
    public int? RoleId
    {
        get 
        { 
             return (roleId = roleId.GetValueOrDefault(this.Relationhip == null ? null : this.Relationhip.FirstOrDefault().TypeList.FirstOrDefault().Id()));
        }
        set { roleId = value; }
    }