[英]“Value cannot be null. Parameter name: source” while add item from connected table in View
in my project i have Two table: Restaurant(RestaurantId, Name, ...., Adress) and RestaurantReviews(ReviewsId, Mark, ...., RestaurantId).在我的项目中,我有两个表:Restaurant(RestaurantId, Name, ...., Adress) 和 RestaurantReviews(ReviewsId, Mark, ...., RestaurantId)。 In my PartialView i try show Restaurant info and calculate Average Mark, but if i try calculate Average i getting error:
在我的 PartialView 中,我尝试显示餐厅信息并计算平均分数,但如果我尝试计算平均值,则会出现错误:
ArgumentNullException: Value cannot be null. (Parameter 'source')
RestaurantModel餐厅模特
public class Restaurant
{
[Key]
public int RestaurantId{ get; set; }
....
[Required(ErrorMessage = "Restaurant name is empty")]
public string Name{ get; set; }
....
public virtual ICollection<RestaurantReviews> RestaurantReviews{ get; set; }
RestaurantReviewsModel餐厅评论模型
public class RestaurantReviews
{
[Key]
public int RestaurantReviewsId { get; set; }
....
[Required(ErrorMessage = "Restaurant mark is empty")]
public int Mark{ get; set; }
[ForeignKey("Restaurant")]
public int RestaurantId { get; set; }
public virtual Restaurant Restaurant {get; set; }
DbContext数据库上下文
public DbSet<Restaurant> Restaurant { get; set; }
public DbSet<RestaurantReviews> RestaurantReviews{ get; set; }
Called PartialViews称为部分视图
@await Html.PartialAsync("~/Views/Restaurant/RestaurantWidget.cshtml", (IEnumerable<Firma.Data.Data.CMS.Restaurant>)ViewBag.RestaurantWidget)
RestaurantWidget.cshtml RestaurantWidget.cshtml
@model IEnumerable<Firma.Data.Data.CMS.Restaurant>
@foreach (var item in Model)
{
...
@item.Name
...
//Without this line everything is ok
@item.RestaurantReviews.Average(x=>x.Mark)
//Without this line everything is ok
...
}
Controller Controller
public IActionResult Index()
{
ViewBag.RestaurantWidget=
(
from restaurant in _context.Restaurant
select restaurant
).Take(5).ToList();
return View();
}
Additional info: Each restaurant has at least one rating.附加信息:每家餐厅至少有一个评级。 There is no restaurant that would not have any rating
没有一家餐厅不会有任何评分
I find answer to my question, in Controller i change我找到了我的问题的答案,在Controller我改变
public IActionResult Index()
{
ViewBag.RestaurantWidget=
(
from restaurant in _context.Restaurant
select restaurant
).Take(5).ToList();
return View();
}
to code below在下面编码
ViewBag.RestaurantWidget= _context.Restaurant.Include(p=>p.RestaurantReviews).Take(4).ToList();
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.