从 ViewBag DotNet Core 设置 SelectedValue

Question

我有以下型号：

public class ActivityType
{
     [Key]
     public int ActivityTypeId { get; set; }
     public string ActivityTypeName { get; set; }
}

public class ActivitySubType
{
     [Key]
     public int ActivitySubTypeId { get; set; }
     public string ActivitySubTypeName { get; set; }
     [ForeignKey("ActivityType")]
     public int ActivityTypeId { get; set; }
     public virtual ActivityType ActivityType { get; set; }
}

public class ActivityRecord
{
     [Key]
     public int ActivityRecordId { get; set; }
     public string ActivityName  { get; set; }
     [ForeignKey("ActivitySubType")]
     public int ActivitySubTypeId { get; set; }
     public virtual ActivitySubType ActivitySubType { get; set; }
}

然后从模型ActivityRecord，我有一个控制器可以保存到数据库中。我正在使用脚手架控制器自动生成。在 Create 视图中，我创建了一个级联下拉代码。选择 ActivityType 时，下拉菜单 ActivitySubType 将根据数据库中的数据生成项目。它保存到数据库（成功）。

情况是，当我尝试编辑记录时。我如何根据 ActivitySubTypeId 的值在 ActivityType 下拉列表中绑定 ActivityTypeId。我已经用下面的代码得到它：

public async Task<IActionResult> Edit(int? id)
{
     var getActivityTypeId = (from a in _db.ActivityRecords
          join b in _db.ActivitySubTypes ON a.ActivitySubTypeId equals b.ActivitySubTypeId
          join c in _db.ActivityTypes ON b.ActivityTypeId equals c.ActivityTypeId
          where a.ActivitySubType == id
          select new {
               b.ActivityTypeId
          }
     ).FirstOrDefault();

     var activityTypeList = (from a in _db.ActivityTypes
                                select new SelectListItem()
                                {
                                    Text = a.ActivityTypeName, Value = a.ActivityTypeId.ToString()
                                }
           ).ToList();

      activityTypeList.Insert(0, new SelectListItem()
      {
          Text = "Select...",
          Value = ""
      });
      ViewBag.ActivityTypeDropList = activityTypeList;
}

在下拉列表中：

<select id="ActivityTypeId" class="form-control form-control-sm" asp-items="@(new SelectList(ViewBag.ActivityTypeDropList,"Value", "Text"))">
</select>

如何将 getActivityTypeId 的结果作为 selectedValue 放入 ActivityType 的下拉列表中？或者是否有其他方法可以实现此目的？
谢谢。

Answer 1

好吧，经过反复试验。我找到了答案：

在视图中：

<select class="form-control form-control-sm" asp-items="ViewBag.ActivityTypeId"></select>

在控制器上：

var selectedValue = (from a in _db.ActivityRecords
                             join b in _db.ActivitySubTypes on a.ActivitySubTypeId equals b.ActivitySubTypeId
                             join c in _db.ActivityTypes on b.ActivityTypeId equals c.ActivityTypeId
                             where a.ActivityRecordId == id
                             select new
                             {
                                 c.ActivityTypeId
                             }
            ).FirstOrDefault();

ViewData["ActivityTypeId"] = new SelectList(_db.ActivityTypes, "ActivityTypeId", "ActivityTypeName", selectedValue.ActivityTypeId.ToString());

感谢您的关注。
干杯，

从 ViewBag DotNet Core 设置 SelectedValue

Set SelectedValue from ViewBag DotNet Core

c#

entity-framework

.net-core

asp.net-core-5.0