问题
New to .Net Core.
Trying to implement a dropdown list similar to: MVC6 Dropdownlist of Countries
In my model class I have
public SelectList SiteList { get; set; }
In my controller, I have:
var sites = _context.Site.OrderBy(s => s.Name).Select(x => new { Id = x.ID, Value = x.Name });
var model = new Issue();
model.SiteList = new SelectList(sites, "Id", "Value");
return View(model);
In my view, I have:
<td class="input-item">
<select asp-for="SiteID" asp-items="@Model.SiteList"></select>
</td>
When I try to implement a migration, I get the following error: The entity type 'Microsoft.AspNetCore.Mvc.Rendering.SelectListGroup' requires a primary key to be defined.
I tried ignoring in my Migrations namespace:
modelBuilder.Entity<Issue>().Ignore(i => i.SiteList);
But I'm not entirely sure that I've done this in the right spot.
回答1:
In order to fix this, simply put
[NotMapped]
above the SelectList property within the model .cs file:
[NotMapped]
public SelectList SiteList { get; set; }
This prevents EntityFramework from mapping the list to the model. Since it's not part of the model database, it doesn't require a primary key.
回答2:
I've run into this issue before. My problem ended up being that while coding my controller I accidentally generated a DbSet for my view model with the List<SelectListItem> on it at the bottom of my ApplicationDbContext.cs file. The [NotMapped] "fix" is more of a band-aid to the problem than actually solving what's causing the error.
Check around your ApplicationDbContext.cs file for a DbSet of the view model that has your List<SelectListItem> on it and remove it.
It should look something like this:public DbSet<TodoItemViewModel> TodoItemViewModel { get; set; }
来源：https://stackoverflow.com/questions/45719579/the-entity-type-microsoft-aspnetcore-mvc-rendering-selectlistgroup-requires-a