c# - EntityFramework 尝试插入未更改的附加实体

Question

我有这样的模型：

public class Parent
{
    public ChildA ChildA { get; set;}
    public ChildB ChildB { get; set;}
}

在我的缓存中，我存储这些对象的集合以供统计。当我尝试保存此集合时，我收到无法添加 ChildA 的错误，因为它违反了主键约束。

            ICollection<Metric> statistics = this.cacheService.Get<ICollection<Metric>>(statisticsCacheKey);
            if (statistics.Any())
            {
                foreach (Parent parent in statistics)
                {
                    this.dataService.Attach<ChildA>(parent.ChildA);
                    this.dataService.Attach<ChildB>(parent.ChildB);

                    this.parentRepository.Create(parent);
                }

                await this.dataService.SaveChangesAsync();
                statistics.Clear();
                this.cacheService.Put<ICollection<Parent>>(statisticsCacheKey, statistics);
            }

ChildA 存在于数据库中并且它附加到上下文中，所以我不明白为什么 EF 试图插入它。我的附加方法看起来像这样

public void Attach<T>(T entity)
        where T : class, IEntity
    {
        EntityState state = context.Entry<T>(entity).State;
        if (state == EntityState.Detached)
        {
            IEnumerable<T> local = (IEnumerable<T>)context.Set<T>().Local;
            bool alreadyAtContext = local.Contains(entity, new EntityComparer());
            if (!alreadyAtContext)
            {
                context.Set<T>().Attach(entity);
            }
        }
    }
}