将对象的永久集合添加到.NET Core中的另一个对象

我正在收集 <AppUser> 其他对象中的对象 Project 反对。

我的模型:

public class Project
    {
        public int ProjectID { get; set; }

        [Required(ErrorMessage = " Please enter a project name")]
        public string Name { get; set; }

        [Required(ErrorMessage = " Please enter a project description")]
        public string Description { get; set; }

        //HERE'S MY COLLECTION OF <APPUSER> OBJECTS
        public virtual ICollection<AppUser> ProjectManagers { get; set; }
    }

在我看来,我需要一封与 <应用程序用户> 添加到此列表中。以下是与此视图关联的ViewModel:

public class AddProjectManagerViewModel
    {
        [Required]
        [EmailAddress(ErrorMessage = "Please ensure email is valid")]
        [UIHint("email")]
        public string Email { get; set; }

        public int ProjectID { get; set; }
    }

以及观点:

@model AddProjectManagerViewModel
@{
    ViewBag.Title = "Add PM";
    Layout = "_Layout";
}
<div class="col-xs-12 buffer">
    <div class="text-center">
        <h3>Enter the new Project Manager's email:</h3>
    </div>
    <div><span asp-validation-for="Email" class="text-danger"></span></div>

    <form asp-action="AddProjectManager">
        <div class="form-group">
            <label asp-for="Email"></label>
            <input asp-for="Email" class="form-control" />
        </div>
        <div class="text-center">
            <button class="btn btn-primary" asp-route-projectId="@Model.ProjectID" type="submit">Add to PMs</button>
        </div>
    </form>
</div>

在我的控制器中,我有post方法。问题是, List<AppUser> 没有坚持并且出现了 null 每次调用action方法时:

[HttpPost]
        [Authorize]
        public async Task<IActionResult> AddProjectManager(int projectId, string email)
        {
            var pmToAdd = await userManager.FindByEmailAsync(email);
            if (pmToAdd != null)
            {
                var proj = repository.Projects.FirstOrDefault(p => p.ProjectID == projectId);
                if(proj != null)
                {
                    //HERE proj.ProjectManagers IS ALWAYS NULL EVEN IF THIS METHOD HAS BEEN PREVIOUSLY CALLED SUCCESSFULLY
                    if(proj.ProjectManagers == null) { proj.ProjectManagers = new List<AppUser>(); }
                    proj.ProjectManagers.Add(pmToAdd);
                    TempData["message"] = $"{pmToAdd.Email} added to {proj.Name} Project Managers";
                    return View("Edit", proj );
                }
                TempData["message"] = $"Error finding project in database.";
                return View();
            }
            TempData["message"] = $"User not found. Ensure that email is linked to a registered user";
            return View();

        }

我应该如何设置这种方法来使模型 public virtual ICollection<AppUser> ProjectManagers { get; set; } 坚持不懈?

编辑 以下是我的存储库方法:

public void AddProjectManager(int projectID, AppUser user)
        {
            Project proj = context.Projects.FirstOrDefault(p => p.ProjectID == projectID);
            if(proj != null)
            {
                proj.ProjectManagers.Add(user);
                context.SaveChanges();
            }
        }

我也变了 proj.ProjectManagers.Add(pmToAdd); 到 repository.AddProjectManager(projectId, pmToAdd); 在行动方法中,但是 List<AppUser>' is still 每次调用时为空