如何从嵌套模型中填充下拉列表?(Asp.net核心MVC)

Question

我有一个嵌套模型，我使用一个名为(BootstrapTool(的模型使视图具有强类型。

我使用ViewBag来填充一个名为(BootstrapCategory(的嵌套模型的下拉列表。但我的问题是，当我从中选择时，总是返回validationnull异常。

引导工具模型

public class BootstrapTool
{
public Guid Id { get; set; }
[MaxLength(100,ErrorMessage ="Max 100")]
[Required]
public string tool { get; set; }
[MaxLength(300, ErrorMessage = "Max 300")]
[Required]
public string descreption { get; set; }
[Required]
public string html { get; set; }
[Required] // here where nisting the other Model BootstrapCategory 
public BootstrapCategory category { get; set; }

}

引导类别模型

public class BootstrapCategory
{
[Key]
public Guid Id { get; set; }
[MaxLength(20)]
[Required]
public string Category { get; set; }
}

控制器

public IActionResult Create()
{
List<BootstrapCategory> bootstrapCategories = _context.bootstrapCategories.ToList();
ViewBag.bpCategories = new SelectList(bootstrapCategories, "Id", "Category");
return View();
}
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create(BootstrapTool bootstrapTool)
{
if (ModelState.IsValid)
{
bootstrapTool.Id = Guid.NewGuid();
_context.Add(bootstrapTool);
await _context.SaveChangesAsync();
return RedirectToAction(nameof(Index));
}
return View(bootstrapTool);
}

下拉列表显示BootstrapCategory
视图

@model BootstrapTool
<div class="row">
<div class="col-10 offset-1">
<form asp-action="Create">
<div asp-validation-summary="ModelOnly" class="text-danger"></div>
<div class="gap-2 d-flex justify-content-between">
<div class="form-group w-50">
<label asp-for="tool" class="control-label"></label>
<input asp-for="tool" class="form-control" />
<span asp-validation-for="tool" class="text-danger"></span>
</div>
<div class="form-group w-50">
<label class="control-label">category</label>
<select asp-for="category.Id" class="form-control" asp-items="@ViewBag.bpCategories">
<option value="" disabled hidden selected>Select Section ...</option>
</select>
<span asp-validation-for="category" class="text-danger"></span>
@*<select asp-for="Id" asp-items="@Html.GetEnumSelectList<Enum>()" class="form-control">
<option value="" hidden disabled selected> -- please selecgt -- </option>
</select>*@
</div>
</div>
<div class="form-group">
<label asp-for="descreption" class="control-label"></label>
<textarea asp-for="descreption" class="form-control" rows="2"></textarea>
<span asp-validation-for="descreption" class="text-danger"></span>
</div>
<div class="form-group mb-2">
<label asp-for="html" class="control-label"></label>
<textarea asp-for="html" class="form-control" rows="5"></textarea>
<span asp-validation-for="html" class="text-danger"></span>
</div>
<div class="form-group mt-3">
<input type="submit" value="Create" class="btn btn-primary d-grid col-6 mx-auto" />
</div>
</form>
</div>
</div>

Answer 1

添加类别ID

public class BootstrapTool
{
[Key]
public Guid Id { get; set; }
[Required] 
public Guid? CategoryId { get; set; }
[ForeignKey(nameof(CategoryId))]
[InverseProperty("BootstrapTools")]
public BootstrapCategory Category { get; set; }

}
public class BootstrapCategory
{
[Key]
public Guid Id { get; set; }
[MaxLength(20)]
[Required]
public string Category { get; set; }
[InverseProperty(nameof(BootstrapTool.Category))]
public virtual ICollection<BootstrapTool> BootstrapTools { get; set; }
}

并修复视图

<select asp-for="CategoryId" class="form-control" asp-items="@ViewBag.bpCategories">
</select>
```