我正在尝试遵循以下教程:ASP.NET Web窗体Web窗体和Visual Studio入门(URL:http://www.asp.net/web-forms/overview/getting-started/getting-started-with-aspnet-45-web-forms/introduction-and-overview)。
我的项目中有其他名称,但想法是一样的。我正在尝试为假日公园的客户创建预订系统。 我做了与教程相同的一切,但是我得到一个错误,我不知道解决方案。在教程中,我在第5步。
我得到的错误是:无法隐式转换类型' System.Data.Entity.DbSet(PortOfTroyCustomers.Models.Accommodation)'到了System.Linq.IQueryable(PortOfTroyCustomers.Accommodation)'。存在显式转换(您是否错过了演员?)
这是Accommodation.aspx.cs的代码(在教程中:ProductList.aspx.cs)这是发生错误的地方:
public partial class Accommodation : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
public IQueryable<Accommodation> GetAccommodations([QueryString("id")] int? sortId)
{
var _db = new PortOfTroyCustomers.Models.PortOfTroyContext();
IQueryable<Accommodation> query = _db.Accommodations; // This is the spot!
if (sortId.HasValue && sortId > 0)
{
query = query.Where(a => a.SortID == sortId); // and this!
}
return query;
}
}
其他代码:
Class Accommodation代码(与教程中的Product.cs几乎相同):
public class Accommodation
{
[ScaffoldColumn(false)]
public int AccommodationID { get; set; }
public short NumberOfGuest { get; set; }
public string ImagePath { get; set; }
[Display(Name = "Richtprijs per week")]
[DataType(DataType.Currency)] // data type op geld zetten voor de double
public double? PricePerWeek { get; set; }
// foreign key
public int? SortID { get; set; }
public int? ResortID { get; set; }
// relaties leggen
public virtual Sort Sort { get; set; }
public virtual Resort Resort { get; set; }
}
类排序代码(与教程中的Category.cs几乎相同):
public class Sort
{
[ScaffoldColumn(false)]
[Display(Name = "Type")]
public int SortID { get; set; }
[Required, StringLength(100), Display(Name = "Name")]
public string Title { get; set; }
[Required, StringLength(10000), DataType(DataType.MultilineText)]
public string Description { get; set; }
public virtual ICollection<Accommodation> Accommodations { get; set; }
}
上下文代码:
public class PortOfTroyContext : DbContext
{
public PortOfTroyContext() : base("PortOfTroyCustomers")
{
}
public DbSet<Sort> Sorts { get; set; }
public DbSet<Accommodation> Accommodations { get; set; }
public DbSet<Resort> Resorts { get; set; }
public DbSet<Facility> Facilities { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
// nieuwe koppeltabel tussen Ficilities en Resorts (is namelijk een TNMT relatie)
modelBuilder.Entity<Facility>()
.HasMany(r => r.Resorts).WithMany(i => i.Facilities)
.Map(t => t.MapLeftKey("FicilityID")
.MapRightKey("ResortID")
.ToTable("FicilityResort"));
}
}
你可以帮我解决这个错误吗?
答案 0 :(得分:4)
当你说: -
var _db = new PortOfTroyCustomers.Models.PortOfTroyContext();
编译器推断赋值右侧的表达式类型,这在C#中称为隐式类型。
现在,您正在尝试分配,这样的查询,我们System.Data.Entity.DbSet
正确&amp;左边的System.Linq.IQueryable
是不同的类型: -
IQueryable<Accommodation> query = _db.Accommodations;
因此,您需要一个明确的类型转换: -
IQueryable<Accommodation> query = (IQueryable<Accommodation>)_db.Accommodations;