将用户添加到角色将重复的用户插入到users表中 [英] Adding user to a role inserts a duplicate user into users table

问题描述

我正在使用Entity Framework代码来管理我的用户的数据库后台。我有一个添加角色到用户操作，从db中提取用户，将该用户添加到角色，然后保存更改。但是，当我这样做时，用户的新副本将使用新的/不同的ID（唯一键）插入到数据库中，而不是从数据库中提取的用户，我不知道为什么。任何关于为什么会发生这种情况的想法？

I'm using Entity Framework code first to manage a database backstore for my users. I have an "add role to user" operation that pulls a user from the db, adds that user to the role, and then saves changes. However, when I do this a new copy of the user is inserted into the database with a new/different ID (unique key) than the user I pulled from the db and I'm not sure why. Any thoughts on why this is happening?

 IEnumerable<long> usersIdsToGiveRole = from u in vm.UsersNotInSelectedRole where u.IsSelected select u.Id; // say, yields "5"
 IEnumerable<User> usersToGiveRole = _userRepository.InternalUsers.Where(u => usersIdsToGiveRole.Contains(u.ID)); // gets user with ID 5
 foreach (var user in usersToGiveRole)
 {
       selectedRole.UsersWithRole.Add(user);
 }


 _roleRepository.SaveChanges(); // creates new user with ID 6 cloning all other fields of user 5

推荐答案

只是一个猜测：您似乎有独立的ObjectContexts for _userRepository 和 _roleRepository 。通过从 _userRepository 加载 usersToGiveRole ，您将附加到此上下文。 selectedRole 似乎附加到 _roleRepository 的其他上下文中。当您将用户添加到 selectedRole.UsersWithRole 时，将其添加到此第二个上下文（用户现在在中添加状态在 _roleRepository 的上下文中）。当您调用此上下文的 SaveChanges 时，将在数据库中创建一个新的User对象。

Just a guess: You seem to have separate ObjectContexts for _userRepository and for _roleRepository. By loading usersToGiveRole from the _userRepository you attach to this context. selectedRole seems to be attached to the other context of _roleRepository. When you add the user to selectedRole.UsersWithRole you add it to this second context (user is now in added state in the context of _roleRepository). When you call SaveChanges of this context now a new User object is created in the database.

解决方案：确保您只在两个存储库中使用一个单一的上下文。

Solution: Make sure that you only use one single context in both repositories.

修改

简短的意思是：

不要这样做：

class UserRepository
{
    private readonly MyContext _context;

    public UserRepository()
    {
        _context = new MyContext();
    }

    public void SaveChanges()
    {
        _context.SaveChanges();
    }
}

class RoleRepository
{
    private readonly MyContext _context;

    public RoleRepository()
    {
        _context = new MyContext();
    }

    public void SaveChanges()
    {
        _context.SaveChanges();
    }
}

...

var userRepository = new UserRepository();
var roleRepository = new RoleRepository();

// CRUD

userRepository.SaveChanges();

// perhaps other CRUD

roleRepository.SaveChanges();

而是这样做：

class UserRepository
{
    private readonly MyContext _context;

    public UserRepository(MyContext context)
    {
        _context = context;
    }
}

class RoleRepository
{
    private readonly MyContext _context;

    public RoleRepository(MyContext context)
    {
        _context = context;
    }
}

...

using (var context = new MyContext())
{
    var userRepository = new UserRepository(context);
    var roleRepository = new RoleRepository(context);

    // CRUD

    context.SaveChanges();
}

上下文（或工作单位）总是位于资源库之上，应在外部创建并注入回收站。

The context (or Unit of Work) is always a level above the repositories, should be created outside and injected into the repos.

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