entity-framework-4.1 - 无法隐式转换类型'System.Collections.Generic.IEnumerable 我在我的 asp.net mvc wen 应用程序中定义了以下模型类：- public class CustomerDetails { public AccountDefinition AccountDefinition {get; set;}

Question

我在我的 asp.net mvc wen 应用程序中定义了以下模型类：-

public class CustomerDetails
{
    public AccountDefinition AccountDefinition {get; set;}
    public SDOrganization SDOrganization {get; set;}
    public ICollection<SiteDefinition> SiteDefinition { get; set; }
    public ICollection<AaaPostalAddress> AaaPostalAddress { get; set; }
    public ICollection<AaaContactInfo> AaaContactInfo { get; set; }
    public virtual ICollection<UserSiteMapping> UserSiteMapping { get; set; } 
}

然后我编写以下查询：-

var customerDetails = entities.AccountDefinitions
    .Where(a => a.ORG_ID == id)
    .Select(cd => new CustomerDetails
    {
        AccountDefinition = cd,
        SDOrganization = cd.SDOrganization,
        AaaPostalAddress = cd.SDOrganization.AaaPostalAddresses,
        AaaContactInfo = cd.SDOrganization.AaaContactInfoes,
        SiteDefinition = cd.SiteDefinitions,
        UserSiteMapping = cd.SiteDefinitions.Select(p2 => p2.UserSiteMappings) //this is raising the exception
    })
    .SingleOrDefault();

return customerDetails;

但我得到了以下误导性错误：-

无法将类型“System.Collections.Generic.IEnumerable>”隐式转换为“System.Collections.Generic.ICollection”。存在显式转换（您是否缺少演员表？）

我不知道究竟是什么导致了错误，因为我正在选择UserSiteMapping与 SiteDefinition 相关的，并且我将这些分配给 UserSiteMapping 的集合（在我的视图模型中定义）？？？？

Answer 1

改用SelectMany：

UserSiteMapping = cd.SiteDefinitions.SelectMany(p2 => p2.UserSiteMappings)

您可能还需要ToList()或ToArray()致电以切换IEnumerable<T>到ICollection<T>：

UserSiteMapping = cd.SiteDefinitions.SelectMany(p2 => p2.UserSiteMappings).ToList()