数据库表的列中的值的下拉列表-MVC实体框架

Posted 2023-02-23

我在从数据库表的列中创建值的下拉列表时遇到问题。我想创建一个具有值和键的父类别的下拉列表，该键也具有空值。以下是前端表中各列的代码。我已经尝试过各种方法，例如ViewBag，SelectList，MultiSelectList，但还没有运气。我的Dropdownlist将包含Parent Category ID和ParentCategory值。 Category_Int_ID是主键。请帮帮我。谢谢。

List<Category> c1 = db.Categories.ToList();
List<Category> c2 = db.Categories.ToList();

      var catview = from ch in c1
                    join pa in c2 on ch.PARENT_CATEGORY_ID equals pa.CATEGORY_INT_ID into tab1
                    from pa in tab1.DefaultIfEmpty()
                    orderby ch.DISPLAY

                              select new Category
                              
                                  DISPLAY = ch.DISPLAY,
                                  ParentCategory = (pa == null ? string.Empty : pa.DISPLAY),
                                  DESCRIPTION = ch.DESCRIPTION,
                                  CATEGORY_INT_ID = ch.CATEGORY_INT_ID

                              ;

答案

 List<Category> c1 = db.Categories.ToList();
                List<Category> c2 = db.Categories.ToList();

                var catview = from ch in c1
                              join pa in c2 on ch.PARENT_CATEGORY_ID equals pa.CATEGORY_INT_ID into tab1
                              from pa in tab1.DefaultIfEmpty()


                              select new Category
                              
                                  PARENT_CATEGORY_ID = ch.PARENT_CATEGORY_ID,
                                  ParentCategory = pa == null ? "" : pa.DISPLAY,


                              ;
                var categ11 = catview.ToList().Where(w=>w.PARENT_CATEGORY_ID !=null).Select(c => new SelectListItem()
                
                    Value = c.PARENT_CATEGORY_ID.ToString(),
                    Text = c.ParentCategory
                ).Distinct();
                ViewBag.Categories = categ11.ToList().Distinct();

在视图中

 @html.DropDownList("ParentCategoryList", (IEnumerable<SelectListItem>)ViewBag.Categories)