尽管模型有效，但 TryValidateModel 返回 false

Question

我有一个控制器，它使用模型绑定从表单中检索数据。我需要在验证之前对模型进行一些编辑，所以我按照文档的建议使用 TryValidateModel。但是由于某种原因，即使“用户”不为空，“作者”总是无效的。真的很困惑这里发生了什么，非常感谢任何帮助。

调试器显示有效模型：

控制器：

    [Authorize]
    [HttpPost]
    public async Task<IActionResult> Create([Bind("Id, Title, Content")] Post post)
    {
        var user = await userManager.GetUserAsync(User);
        post.Author = user;
        post.UpvotedBy.Add(user);

        if (post.Title != null && post.Content != null)
        {
            post.Title = post.Title.Trim();
            post.Content = post.Content.Trim();
        }

        if (TryValidateModel(post))  // Never true
        {
            context.Add(post);
            context.SaveChanges();

            return RedirectToAction("Details", new { id = post.Id });
        }
        else return View(post);
    }

型号：

public abstract class Entry
    {
        public Entry()
        {
            DateCreated = DateTime.Now;
            Upvotes = 1;
            Downvotes = 0;
            VoteScore = 1;

            Replies = new List<Comment>();
            SavedBy = new List<ApplicationUser>();
            HiddenBy = new List<ApplicationUser>();
            UpvotedBy = new List<ApplicationUser>();
            DownvotedBy = new List<ApplicationUser>();
        }

        public int Id { get; set; }

        [Required, StringLength(40000)]
        public string Content { get; set; }

        [Required, DataType(DataType.DateTime)]
        public DateTime DateCreated { get; set; }

        [Required]
        public int Upvotes { get; set; }
        [Required]
        public int Downvotes { get; set; }
        [Required]
        public int VoteScore { get; set; }

        [Required]
        public ApplicationUser Author { get; set; }
        [Required]
        public ICollection<Comment> Replies { get; set; }
        [Required]
        public ICollection<ApplicationUser> SavedBy { get; set; }
        [Required]
        public ICollection<ApplicationUser> HiddenBy { get; set; }
        [Required]
        public ICollection<ApplicationUser> UpvotedBy { get; set; }
        [Required]
        public ICollection<ApplicationUser> DownvotedBy { get; set; }
    }

    public class Post : Entry
    {
        [Required, StringLength(300, MinimumLength = 1)]
        public string Title { get; set; }
    }

表格：

@model Post
@{
    ViewData["Title"] = "New post";
}

<div class="container">
    <form asp-action="Create">
        <div class="form-group mb-3">
            <h3>Title</h3>
            <input asp-for="Title" class="form-control bg-dark text-white border-secondary" 
                   placeholder="Make it descriptive!"/>
            <span asp-validation-for="Title" class="text-danger"></span>
        </div>
        <div class="form-group mb-3">
            <h3>Content</h3>
            <textarea asp-for="Content" class="form-control bg-dark text-white border-secondary" 
                      placeholder="What do you have to say?" rows="5"></textarea>
            <span asp-validation-for="Content" class="text-danger"></span>
        </div>

        <a href="javascript:history.go(-1)" class="btn btn-outline-danger" role="button">
            <i class="fas fa-ban me-1"></i> Cancel
        </a>
        <button type="submit" class="btn btn-outline-primary">
            <i class="fas fa-save me-1"></i> Submit
        </button>
    </form>
</div>

Answer 1

在调用TryValidate之前尝试清除ModelState：

// your model update code
ModelState.Clear();
if (TryValidateModel(post))
{
    ....
}

另一种选择是在验证发生之前实现custom model binder 以通过UserManager 绑定Author。