实体框架中的mvc插入不能为null错误

Question

I am getting an exception that says the user email cannot be null. The User.Identity.Name; is set to the users email address however when I try to create a new post the exception is thrown saying:

Cannot insert the value NULL into column 'BlogUserEmail', table
'Blog.dbo.Posts'; column does not allow nulls. INSERT fails.\r\nThe
statement has been terminated.

Im not sure how to add the users email address using the User.Identity.Name; to the Post create method. It works fine in my authentication method using User.Identity.Name; . However I created some extra tables in Entity Framework 5 and in the Post table I have the BlogUserEmail as a Foreign Key:

![enter image description here][1]

View:

@model MyBlogger.Post

@{
    ViewBag.Title = "Create";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>Create</h2>

@using (Html.BeginForm()) {
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)

    <fieldset>
        <legend>Post</legend>

        <div class="editor-label"> // I changed this area
            @Html.LabelFor(model => model.BlogUserEmail, User.Identity.Name)
        </div>
        <div class="editor-field">
            @Html.ValidationMessageFor(model => model.BlogUserEmail)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.CategoryId, "Category")
        </div>
        <div class="editor-field">
            @Html.DropDownList("CategoryId", String.Empty)
            @Html.ValidationMessageFor(model => model.CategoryId)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Title)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Title)
            @Html.ValidationMessageFor(model => model.Title)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.ShortDescription)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.ShortDescription)
            @Html.ValidationMessageFor(model => model.ShortDescription)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Description)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Description)
            @Html.ValidationMessageFor(model => model.Description)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Meta)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Meta)
            @Html.ValidationMessageFor(model => model.Meta)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.UrlSlug)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.UrlSlug)
            @Html.ValidationMessageFor(model => model.UrlSlug)
        </div>


        <div class="editor-label">
            @Html.LabelFor(model => model.Published)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Published)
            @Html.ValidationMessageFor(model => model.Published)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.PostedOn)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.PostedOn)
            @Html.ValidationMessageFor(model => model.PostedOn)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Modified)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Modified)
            @Html.ValidationMessageFor(model => model.Modified)
        </div>

        <p>
            <input type="submit" value="Create" />
        </p>
    </fieldset>

Answer 1

Since you are picking this up from User.Identity.Name, you can assign it in the HttpPost method.

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(Post post)
{
    post.BlogUserEmail = User.Identity.Name
    try
    {
        if (ModelState.IsValid)
        {
            db.Posts.Add(post);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

        var email = User.Identity.Name;
        ViewBag.BlogUserEmail = new SelectList(db.BlogUsers, email);
        ViewBag.CategoryId = new SelectList(db.Categories, "Id", "Name", post.CategoryId);
        return View(post);
    }
    catch (DbEntityValidationException e)
    {
        var newException = new FormattedDbEntityValidationException(e);
        throw newException;
    }

}

Since it is not an editable field in the Create View, you can also take an approach of putting in a HiddenField.

Remember that readonly labels will not bind to your model in the Post method.

Answer 2

If the email can be change in the post form, maybe not now, but in time, you can add it as hidden field with a default value.

@using (Html.BeginForm()) {
@Html.AntiForgeryToken()
@Html.ValidationSummary(true)

<fieldset>
    <legend>Post</legend>

    <div class="editor-label"> // I changed this area
        @Html.LabelFor(model => model.BlogUserEmail, User.Identity.Name)
    </div>
    <div class="editor-field">
        @Html.ValidationMessageFor(model => model.BlogUserEmail)
    </div>
    @* Hidden Field *@
    @Html.HiddenFor(model => model.BlogUserEmail,new { value = User.Identity.Name })

    // rest of the html