实体框架多对多不断添加额外记录
我尝试首先使用实体框架代码将新记录添加到链接表中。我拥有的是 User 和 Role 上的多对多。我遇到的情况是，当我更改用户的角色时，我删除他们以前的所有角色并添加新角色，如下所示：
//Delete all associated roles for user
var roleUser = db.Users.Include(r => r.Roles).FirstOrDefault(u => u.UserId == user.UserId);
var usersRoles = roleUser.Roles;
usersRoles.ForEach(role => roleUser.Roles.Remove(role));
//add the new roles
roleUser.Roles.AddRange(detachedUser.Roles);
db.SaveChanges();
因此它完美地删除了它们。但是当添加新角色时，它不仅将其添加到链接表中，而且还添加到Role表中。添加一个全新的角色，没有 RoleName。 user.Roles 将包含一个具有以下数据的项目：
RoleId;//1 <-- this Id exists in the database already but yet still it creates one instead of a linktable record.
RoleName;//null
如何防止 EF 添加全新记录并仅向链接表添加一条记录？
更新：我最终这样做了：
var roleUser = db.Users.Include(r => r.Roles).FirstOrDefault(u => u.UserId == user.UserId);
var roles = db.Roles;
foreach (var role in roles)
{
if (user.Roles.Any(r => r.RoleId == role.RoleId))
{
roleUser.Roles.Add(role);
}
else
{
roleUser.Roles.Remove(role);
}
}
db.SaveChanges();
I'm trying to add a new record to the link table using entityframework code first. What I have is a many to many on User and Role. The scenario I have is that when I'm changing a role for the user, I delete all their previous roles and add the new roles as follows:
//Delete all associated roles for user
var roleUser = db.Users.Include(r => r.Roles).FirstOrDefault(u => u.UserId == user.UserId);
var usersRoles = roleUser.Roles;
usersRoles.ForEach(role => roleUser.Roles.Remove(role));
//add the new roles
roleUser.Roles.AddRange(detachedUser.Roles);
db.SaveChanges();
So it removes them perfectly. But when adding new roles, it doesn't only add it to the link table but also the Role table. A completely new role gets added without a RoleName. user.Roles would contain an item with the following data:
RoleId;//1 <-- this Id exists in the database already but yet still it creates one instead of a linktable record.
RoleName;//null
How do I prevent EF from adding a whole new record and just add a record to the link table?
Update: I ended up doing this:
var roleUser = db.Users.Include(r => r.Roles).FirstOrDefault(u => u.UserId == user.UserId);
var roles = db.Roles;
foreach (var role in roles)
{
if (user.Roles.Any(r => r.RoleId == role.RoleId))
{
roleUser.Roles.Add(role);
}
else
{
roleUser.Roles.Remove(role);
}
}
db.SaveChanges();
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评论（3）
在向用户添加新角色之前尝试保存
编辑：
看看这个：
user.Roles来自哪里？try to save before adding new roles to the user
Edit:
Have a look at this :
where do
user.Rolescome from ?我认为您遇到的问题是您需要在将角色添加到用户之前附加角色。
您也不需要将它们全部删除，只需删除那些已删除的，然后只添加新的。
I think the problem you have is that you need to attach your Roles before adding them to the user.
you also don't need to remove them all, simply remove those removed and then only add the new ones.
对于您添加的每个卷，您可以尝试检查或设置实体状态。例如，这里我将集合设置为未更改。这样它就不会尝试插入或更新它。
更多信息请点击这里：
http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add -attach-and-entity-states.aspx
For each roll that you add you could try checking or setting the entity state. For example here I set the set to unchaged. This way it wont attempt to insert or update it.
More info here:
http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx