ASP.Net MVC创建寄存器错误

Question

I have this thing running at my application. I have 3 tables, 1 main table and 2 other tables that are needed to create the main table, the main table depends on the 2 tables, they are connected with constraints. I have the main table: Word Then I have the two other tables: Difficulties and Category. I created the Difficulty: Easy and then I created the Category: Nature. So now, I would be able to create as many words as I could with those 2 attributes, but it gives me an error. I can only create a word if I create this way

Dificulty -> Category -> Word

or

Category -> Difficulty -> Word

. I can't create a word without making that path and I don't know why. The values are stored in a database that will be called in 2 ComboBoxes, 1 for the Difficulty and the other one for Category. If I wanted to create a word I would need to create a new category and a new difficulty otherwise it will return as null.

This is my Model View:

public partial class palavra
    {
        public int id_pal { get; set; }
        public Nullable<int> LETRAS { get; set; }
        public string PISTA { get; set; }
        public int id_cat { get; set; }
        public int id_dificuldade { get; set; }
        public string nomepalavra { get; set; }

        public virtual  categoria categoria { get; set; }
       public virtual dificuldade dificuldade { get; set; }
    }

This is my Controller:

public ActionResult Index()
        {
            var palavras = db.palavras.Include(p => p.categoria).Include(p => p.dificuldade);
           return View(palavras.ToList());
        }



        // GET: palavras/Create
        public ActionResult Create()
        {
            ViewBag.id_cat = new SelectList(db.categorias, "id_cat", "TIPO_CATEGORIA");
            ViewBag.id_dificuldade = new SelectList(db.dificuldades, "id_dificuldade", "TIPO_DIFICULDADE");
            return View();
        }

        // POST: palavras/Create
        // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
        // more details see http://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Create([Bind(Include = "id_pal,LETRAS,PISTA,id_cat,id_dificuldade,nomepalavra")] palavra palavra)
        {
            if (ModelState.IsValid)
            {
                db.palavras.Add(palavra);
                db.SaveChanges();
                return RedirectToAction("Index");
            }

            ViewBag.id_cat = new SelectList(db.categorias, "id_cat", "TIPO_CATEGORIA", palavra.id_cat);
            ViewBag.id_dificuldade = new SelectList(db.dificuldades, "id_dificuldade", "TIPO_DIFICULDADE", palavra.id_dificuldade);
            return View(palavra);
        }

This is my view:

<p>
    @Html.ActionLink("Create New", "Create")
</p>
<table class="table">
    <tr>
        <th>
            @Html.DisplayNameFor(model => model.nomepalavra)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.LETRAS)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.PISTA)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.categoria.TIPO_CATEGORIA)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.dificuldade.TIPO_DIFICULDADE)
        </th>
        <th></th>
    </tr>

@foreach (var item in Model) {
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.nomepalavra)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.LETRAS)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.PISTA)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.categoria.TIPO_CATEGORIA)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.dificuldade.TIPO_DIFICULDADE)
        </td>
        <td>
            @Html.ActionLink("Edit", "Edit", new { id=item.id_pal }) |
            @Html.ActionLink("Details", "Details", new { id=item.id_pal }) |
            @Html.ActionLink("Delete", "Delete", new { id=item.id_pal })
        </td>
    </tr>
}

Whenever I run my code to insert I get this error:

An exception of type 'System.Data.Entity.Infrastructure.DbUpdateException' occurred in EntityFramework.dll but was not handled in user code

Additional information: An error occurred while updating the entries. See the inner exception for details.

When I check the Details it appears that the "Category" table and the "Difficulty" table are null but the others fields are all with the info that I gave them.

My Database Schema is the following:

Category connects to Word and Difficulty connects to Word.

Both Category and Difficulty are a 1 to many relationship with the table Word.

Answer 1

if you are use entity framework you need to defined your constraint at your model there is 2 options, code first or database first

here my example with database first

Database First

after you generate your model from db, easy step to create create update delete with scaffolding

Scaffolding crud

with scaffolding you much easier to create crud, and if any constraint

example above you create work with selecting Difficulty / Category yes your dropdownlist will be created automatically

example my codes menu creator controller

   // GET: SystemMenus/Create
    public IActionResult Create()
    {
        ViewData["ParentId"] = new SelectList(_context.SystemMenus, "Id", "Name");      
        ViewData["Color"] = new SelectList(OptionDropdown.GetBackgroundColor(), "Value", "Text");
        ViewData["Size"] = new SelectList(OptionDropdown.GetSize(), "Value", "Text");
        ViewData["Module"] = new SelectList(OptionDropdown.GetModule(), "Value", "Text");
        return View();
    }

    // POST: SystemMenus/Create
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see http://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Create([Bind("Id,Name,Controller,Action,ParentId,Icon,Module,Description,FixHeader,Color,Size")] SystemMenu systemMenu)
    {
        if (ModelState.IsValid)
        {
            _context.Add(systemMenu);
            await _context.SaveChangesAsync();
            return RedirectToAction(nameof(Index));
        }
        ViewData["ParentId"] = new SelectList(_context.SystemMenus, "Id", "Name", systemMenu.ParentId);
        ViewData["Color"] = new SelectList(OptionDropdown.GetBackgroundColor(), "Value", "Text", systemMenu.Color);
        ViewData["Size"] = new SelectList(OptionDropdown.GetSize(), "Value", "Text", systemMenu.Size);
        ViewData["Module"] = new SelectList(OptionDropdown.GetModule(), "Value", "Text", systemMenu.Module);
        return View(systemMenu);
    }

and here my model with recursive constraint parentid

 public class SystemMenu
{
    public SystemMenu()
    {
        Details = new HashSet<SystemMenu>();
    }


    [Key]
    public int Id { get; set; }

    [StringLength(50)]
    public string Name { get; set; }

    [StringLength(50)]
    public string Controller { get; set; }
    [StringLength(50)]
    public string Action { get; set; }

    [ForeignKey("ParentId")]

    public SystemMenu Parent { get; set; }
    [Display(Name = "Parent")]
    public int? ParentId { get; set; }
    [StringLength(50)]
    public string Icon { get; set; }

    [StringLength(50)]
    public string Module { get; set; }

    [StringLength(200)]
    [DataType(DataType.MultilineText)]
    public string Description { get; set; }
    public bool FixHeader { get; set; }

    [StringLength(50)]
    public string Color { get; set; }

    [StringLength(50)]
    public string Size { get; set; }

    public ICollection<SystemMenu> Details { get; set; }
}

here's my views

enter code 

 @model NCFramework.Models.System.SystemMenu @{ ViewData["Title"] = "Create"; Layout = "~/Views/Shared/_Layout.cshtml"; } <div class="row"> <div class="col-md-4"> <form asp-action="Create"> <div asp-validation-summary="ModelOnly" class="text-danger"></div> <div class="form-group"> <label asp-for="Name" class="control-label"></label> <input asp-for="Name" class="form-control" /> <span asp-validation-for="Name" class="text-danger"></span> </div> <div class="form-group"> <label asp-for="Controller" class="control-label"></label> <input asp-for="Controller" class="form-control" /> <span asp-validation-for="Controller" class="text-danger"></span> </div> <div class="form-group"> <label asp-for="Action" class="control-label"></label> <input asp-for="Action" class="form-control" /> <span asp-validation-for="Action" class="text-danger"></span> </div> <div class="form-group"> <label asp-for="ParentId" class="control-label"></label> <select asp-for="ParentId" class ="form-control" asp-items="ViewBag.ParentId"> <option value="">Select</option> </select> </div> <div class="form-group"> <label asp-for="Icon" class="control-label"></label> <input asp-for="Icon" class="form-control" /> <span asp-validation-for="Icon" class="text-danger"></span> </div> <div class="form-group"> <label asp-for="Module" class="control-label"></label> <select asp-for="Module" class="form-control" asp-items="ViewBag.Module"> <option value="">Select</option> </select> <span asp-validation-for="Module" class="text-danger"></span> </div> <div class="form-group"> <label asp-for="Description" class="control-label"></label> <input asp-for="Description" class="form-control" /> <span asp-validation-for="Description" class="text-danger"></span> </div> <div class="form-group"> <div class="mt-checkbox-list"> <label class="mt-checkbox mt-checkbox-outline"> @Html.DisplayNameFor(model => model.FixHeader) <input asp-for="FixHeader" class="checkbox-inline" /> <span></span> </label> </div> </div> <div class="form-group"> <label asp-for="Color" class="control-label"></label> <select asp-for="Color" class="form-control" asp-items="ViewBag.Color"> <option value="">Select</option> </select> <span asp-validation-for="Color" class="text-danger"></span> </div> <div class="form-group"> <label asp-for="Size" class="control-label"></label> <select asp-for="Size" class="form-control" asp-items="ViewBag.Size"> <option value="">Select</option> </select> <span asp-validation-for="Size" class="text-danger"></span> </div> <div class="form-group"> <input type="submit" value="Create" class="btn btn-default" /> </div> </form> </div> </div> <div> <a asp-action="Index">Back to List</a> </div> @section Scripts { @{await Html.RenderPartialAsync("_ValidationScriptsPartial");} } 

here

the example with asp.net core mvc also you can try with visual studio, these 3 files generated by scaffolding with defined model first

hoe this helps

cheers