entity-framework-4 - 无法创建类型为 'T' 的常量值。在此上下文中仅支持原始类型 ('such as Int32, String, and Guid' )

Question

我看到很多关于此错误的问题，但有人可以告诉我为什么我的代码中出现此错误？
我的应用程序中有用户和组，它们有很多关系:

public class Group
{
    [Key]
    public int GId { get; set; }

    public string GName { get; set; }

    public virtual ICollection<UserProfile> Members { get; set; }

    public Group()
    {
        Members = new HashSet<UserProfile>();
    }
}
public class UserProfile
{
    [Key]
    public Guid UserId { get; set; }

    [Required]
    public string UserName { get; set; }

    public virtual ICollection<Group> Groups { get; set; }

    public UserProfile()
    {
        Groups = new HashSet<Group>();

    }
}

我想获得用户加入的所有组并将其传递给 ViewBag，因此:

UserProfile user = core.Profiles.Find(1);
//ok, no error in controller, but view...
ViewBag.JoinGroups = core.Groups.Where(g => g.Members.Contains(user));

但我在 View 中收到错误:

@if (ViewBag.JoinGroups != null)
{
    foreach (var g in ViewBag.JoinGroups)//My issue start here
    {
        <p>@g.GId</p>
    }
}

它说:

Unable to create a constant value of type 'Project.Model.UserProfile'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.

我错过了什么吗？

Answer 1

消息很明确:EF Linq 查询不支持传递实体。

您可以通过更改此部分来解决它:

UserProfile user = core.Profiles.Find(1);
ViewBag.JoinGroups = core.Groups.Where(g => g.Members.Contains(user));

为了这:

ViewBag.JoinGroups = core.Groups.Where(g => g.Members.Select(x => x.UserId)
                                                     .Contains(1));