<分区>
我有一个简单的 2 表数据库,其中包含用户和组。以下是表格的列:
用户:
- 用户名
- 用户名
- 组号
群组:
- 组号
- 组名
下面是生成的类:
public partial class Group
{
public Group()
{
this.Users = new HashSet<User>();
}
public int GroupID { get; set; }
public string GroupName { get; set; }
public virtual ICollection<User> Users { get; set; }
}
-
public partial class User
{
public int UserID { get; set; }
public string UserName { get; set; }
public Nullable<int> GroupID { get; set; }
public virtual Group Group { get; set; }
}
我需要制作一种方法,将用户插入到给定的组中。如果该组不存在,则应创建它。我正在使用 Entity Framework 。这是一些代码:
public class Entry
{
public static void Main()
{
using (var dbContext = new UserSystemEntities())
{
var user = new User();
user.UserName = "h4x0r";
AddUserToGroup(dbContext, "Admins", user);
Console.WriteLine("User {0} added successfully.", user.UserName);
}
}
public static void AddUserToGroup(UserSystemEntities dbContext, string groupName, User user)
{
using (var dbTransaction = dbContext.Database.BeginTransaction())
{
var group = dbContext.Groups.FirstOrDefault(x => x.GroupName == groupName);
try
{
if (group == null)
{
var newGroup = new Group();
newGroup.GroupName = groupName;
dbContext.Groups.Add(newGroup);
}
dbContext.Groups.FirstOrDefault(x => x.GroupName == group.GroupName).Users.Add(user);
dbContext.SaveChanges();
}
catch(Exception ex)
{
Console.WriteLine("Error occured! " + ex.message);
dbTransaction.Rollback();
}
dbTransaction.Commit();
}
}
}
将用户添加到组中时出现问题:
dbContext.Groups.FirstOrDefault(x => x.GroupName == group.GroupName).Users.Add(user);
抛出一个 Null Reference Exception,我就是想不通为什么。现在盯着它大约20分钟,仍然找不到答案。为什么我想念?