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我有一个动作 SearchPost。在获取操作中：

       ViewBag.cities = db.cities.ToList();
        ViewBag.areas = db.areas.ToList();
      IEnumerable<SelectListItem> Months =pm.GetMyMonthList().Select(a => new      
              SelectListItem  {
                    Value = a.Value,
                    Text = a.Text
                }).ToList();
        ViewBag.monthList = Months;
        IEnumerable<SelectListItem> rentTypes = pm
                .GetRentType()
                .Select(a => new SelectListItem
                {
                    Value = a.Value,
                    Text = a.Text
                })
                .ToList();

        ViewBag.typeList = rentTypes;
        return View(db.posts.Include("user").ToList());

在查看页面

        @Html.DropDownList("City",new SelectList(ViewBag.cities as 
         System.Collections.IEnumerable, "city_id", "name"),
          "Select City", new { id = "ddlCars" }) 
         @Html.DropDownList("Area", new SelectList(Enumerable.Empty<SelectListItem>(), 
          "area_id", "name"),
          "Select Area", new { id = "ddlModels" })
        @Html.DropDownList("rent_type", new SelectList(ViewBag.typeList as    
         System.Collections.IEnumerable, "Value", "Text"), "Select Category")       
       @Html.DropDownList("month", new SelectList(ViewBag.monthList as 
        System.Collections.IEnumerable, "Value", "Text"), "Select Month")

在我的发布操作中：

         IList<post> p = db.posts.Include("user").ToList();
          string Area = Request.Form["Area"];
          string City = Request.Form["City"];
            if (City != "Select City" && City != null && City !="")
            {
                int c_id = Convert.ToInt32(City);
                city c = db.cities.Single(s => s.city_id == c_id);
                ci = c.name;
            }
            if (Area != "Select Area" && Area != null && Area !="")
            {
                int a_id = Convert.ToInt32(Area);
                area a = db.areas.Single(x => x.area_id == a_id);
                ar = a.name;
            }
         string rent_type = Request.Form["rent_type"];
         string month = Request.Form["month"];
          if (rent_type != null && rent_type != "")
            {
                if ((p != null) && (p.Any()))
                {
                    p = p.Where(a => a.rent_type == rent_type).ToList();
                }
            }
            if (month!= null && month != "")
            {
                if ((p != null) && (p.Any()))
                {

                    p = p.Where(a => a.rent_month == month).ToList();

                }
            }
         return View(p);

在这里，我首先从我的数据库中选择了所有帖子。然后我想按城市、地区、月份和租金类型过滤它。城市和地区是级联下拉列表。当我选择城市和地区时，它会正确过滤记录。但如果我只选择城市它会给出错误：

序列不包含任何元素

在线：

面积 a = db.areas.Single(x => x.area_id == a_id);

当我尝试仅按月或rent_type 过滤时，它没有过滤记录并且总是不提供任何记录。

我应该更改哪部分代码来解决这两个问题......

提前致谢...

4

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