从数据库中创建一个选择框列表并将其显示在 asp.net mvc 的视图中

Question

I used this code for making data for selectbox and used viewbag to send it to view:

 ViewBag.category_id = new SelectList(db.categories, "id", "title");
                return View();

and in my view to show the selectbox I used this code:

@Html.DropDownList("category_id", null, htmlAttributes: new { @class = "form-control" })

but when I run my project I get this error: System.InvalidOperationException: 'The operation cannot be completed because the DbContext has been disposed.'

Answer 1

db.Categories is a lazy-loaded IEnumerable<> of all of the categories in your database. You should use ToList() to evaluate that IEnumerable<> just like you did with your other queries:

ViewBag.category_id = new SelectList(db.categories.ToList(), "id", "title");