实体框架- lambda表达式中的NotSupportedException

在我的MVC应用程序ApplicationUser和Employee类有1-1关系:

public class ApplicationUser : IdentityUser
    {
        public Employee Employee { get; set; }
    }
public class Employee
    {
        [Key]
        public virtual ApplicationUser ApplicationUser { get; set; }
        public virtual string Name { get; set; }
    }

在公共静态类

中

我有以下方法:

public static ApplicationUser GetCurrentApplicationUser(string userName)
        {
            using (DbContext db = new DbContext())
            {
                return db.Users.FirstOrDefault(u => u.UserName.Equals(userName));
            }
        }
public static Employee GetEmployeeByApplicationUser(string userName)
        {
            using (DbContext db = new DbContext())
            {
                return db.Employees.SingleOrDefault(e => e.ApplicationUser == GetCurrentApplicationUser(userName));
            }
        }

如你所见，

第二个方法正在使用第一个方法。但我得到以下错误:

System.NotSupportedException was unhandled by user code
Message=LINQ to Entities does not recognize the method 'GetCurrentApplicationUser(System.String)' method, and this method cannot be translated into a store expression.

但是如果我将第一个方法中的内部代码粘贴到第二个方法中，就像下面这样，它可以正常工作。

return db.Employees.SingleOrDefault(e => e.ApplicationUser == db.Users.FirstOrDefault(u => u.UserName.Equals(userName)));

我在这里错过了什么?为什么会出现这个错误?

谢谢!

using (DbContext db = new DbContext())
{
    db.Connection.Open();
    Employee currentApplicationUser = db.Users.FirstOrDefault(u => u.UserName.Equals(userName));
    currentApplicationUserEmployee = db.Employees.SingleOrDefault(e => e.ApplicationUser == currentApplicationUser);
    db.Connection.Close();
    return currentApplicationUserEmployee;
}