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[英]Value cannot be null. Parameter name: source
[英]“Value cannot be null. Parameter name: source” while add item from connected table in View
在我的项目中,我有两个表:Restaurant(RestaurantId, Name, ...., Adress) 和 RestaurantReviews(ReviewsId, Mark, ...., RestaurantId)。 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')
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; }
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; }
数据库上下文
public DbSet<Restaurant> Restaurant { get; set; }
public DbSet<RestaurantReviews> RestaurantReviews{ get; set; }
称为部分视图
@await Html.PartialAsync("~/Views/Restaurant/RestaurantWidget.cshtml", (IEnumerable<Firma.Data.Data.CMS.Restaurant>)ViewBag.RestaurantWidget)
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
public IActionResult Index()
{
ViewBag.RestaurantWidget=
(
from restaurant in _context.Restaurant
select restaurant
).Take(5).ToList();
return View();
}
附加信息:每家餐厅至少有一个评级。 没有一家餐厅不会有任何评分
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();
}
在下面编码
ViewBag.RestaurantWidget= _context.Restaurant.Include(p=>p.RestaurantReviews).Take(4).ToList();
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