如何删除关系.HasOptional().WithMany() (EntityFramework)

Question

我有两个带有关系的表：

    modelBuilder.Entity<User>()
        .HasOptional(u => u.Subscription)
        .WithMany();

如何删除关系？我想删除订阅，但离开所有用户。如果我删除订阅EF抛出异常：

"The DELETE statement conflicted with the REFERENCE constraint
\"FK_Users_Subscriptions_Subscription_Id\". 
The conflict occurred in database \"db\",table \"dbo.Users\",
column 'Subscription_Id'.\r\nThe statement has been terminated.

我想拥有从用户到订阅的访问权限。

Answer 1

删除订阅时，必须确保具有该订阅的所有用户的订阅引用都设置为null，否则会违反数据库中的外键约束。我认为，将要删除的订阅加载到上下文中就足够了。EF将自动修复这些关系：

using (var ctx = new MyContext())
{
    var subscriptionToDelete = ctx.Subscriptions.Find(subscriptionToDeleteId);
    ctx.Users.Where(u => u.Subscription.Id == subscriptionToDeleteId).Load();

    ctx.Subscriptions.Remove(subscriptionToDelete);

    ctx.SaveChanges();
}