我发现这个答案对同样的错误更有帮助。 EF似乎不喜欢它当你删除，它更喜欢删除。

您可以像这样删除附加到记录上的记录集合。

order.OrderDetails.ToList().ForEach(s => db.Entry(s).State = EntityState.Deleted);

在本例中，所有附加到订单的Detail记录的状态都设置为Delete。(准备添加回更新的详细信息，作为订单更新的一部分)

当我要删除我的记录时，我也遇到了同样的问题，因为这个问题的解决方案是，当你要删除你的记录时，你在删除头/主记录之前丢失了一些东西，你必须写代码在头/主记录之前删除它的细节，我希望你的问题会得到解决。

这种解决方案对我来说很管用:

Parent original = db.Parent.SingleOrDefault<Parent>(t => t.ID == updated.ID);
db.Childs.RemoveRange(original.Childs);
updated.Childs.ToList().ForEach(c => original.Childs.Add(c));
db.Entry<Parent>(original).CurrentValues.SetValues(updated);

重要的是，这将删除所有记录并重新插入它们。 但对于我的情况(少于10)，这是可以的。

我希望这能有所帮助。

You should delete old child items thisParent.ChildItems one by one manually. Entity Framework doesn't do that for you. It finally cannot decide what you want to do with the old child items - if you want to throw them away or if you want to keep and assign them to other parent entities. You must tell Entity Framework your decision. But one of these two decisions you HAVE to make since the child entities cannot live alone without a reference to any parent in the database (due to the foreign key constraint). That's basically what the exception says.

Edit

如果子项目可以添加，更新和删除，我会做什么:

public void UpdateEntity(ParentItem parent)
{
    // Load original parent including the child item collection
    var originalParent = _dbContext.ParentItems
        .Where(p => p.ID == parent.ID)
        .Include(p => p.ChildItems)
        .SingleOrDefault();
    // We assume that the parent is still in the DB and don't check for null

    // Update scalar properties of parent,
    // can be omitted if we don't expect changes of the scalar properties
    var parentEntry = _dbContext.Entry(originalParent);
    parentEntry.CurrentValues.SetValues(parent);

    foreach (var childItem in parent.ChildItems)
    {
        var originalChildItem = originalParent.ChildItems
            .Where(c => c.ID == childItem.ID && c.ID != 0)
            .SingleOrDefault();
        // Is original child item with same ID in DB?
        if (originalChildItem != null)
        {
            // Yes -> Update scalar properties of child item
            var childEntry = _dbContext.Entry(originalChildItem);
            childEntry.CurrentValues.SetValues(childItem);
        }
        else
        {
            // No -> It's a new child item -> Insert
            childItem.ID = 0;
            originalParent.ChildItems.Add(childItem);
        }
    }

    // Don't consider the child items we have just added above.
    // (We need to make a copy of the list by using .ToList() because
    // _dbContext.ChildItems.Remove in this loop does not only delete
    // from the context but also from the child collection. Without making
    // the copy we would modify the collection we are just interating
    // through - which is forbidden and would lead to an exception.)
    foreach (var originalChildItem in
                 originalParent.ChildItems.Where(c => c.ID != 0).ToList())
    {
        // Are there child items in the DB which are NOT in the
        // new child item collection anymore?
        if (!parent.ChildItems.Any(c => c.ID == originalChildItem.ID))
            // Yes -> It's a deleted child item -> Delete
            _dbContext.ChildItems.Remove(originalChildItem);
    }

    _dbContext.SaveChanges();
}

注意:这不是测试。它假设子项集合的类型是ICollection。(我通常有IList，然后代码看起来有点不同。)为了保持简单，我还去掉了所有存储库抽象。

我不知道这是否是一个好的解决方案，但我相信必须按照这些思路做一些艰苦的工作，以处理导航集合中的各种更改。我也很乐意看到一种更简单的方法。

我使用了Mosh的解决方案，但我不清楚如何在代码中正确地实现组合键。

这就是解决方案:

public class Holiday
{
    [Key, Column(Order = 0), DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int HolidayId { get; set; }
    [Key, Column(Order = 1), ForeignKey("Location")]
    public LocationEnum LocationId { get; set; }

    public virtual Location Location { get; set; }

    public DateTime Date { get; set; }
    public string Name { get; set; }
}

我也解决了我的问题与Mosh的答案，我认为PeterB的答案是有点，因为它使用枚举作为外键。请记住，在添加这段代码之后，您将需要添加一个新的迁移。

我也可以推荐这篇博客的其他解决方案:

http://www.kianryan.co.uk/2013/03/orphaned-child/

代码:

public class Child
{
    [Key, Column(Order = 0), DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    public string Heading { get; set; }
    //Add other properties here.

    [Key, Column(Order = 1)]
    public int ParentId { get; set; }

    public virtual Parent Parent { get; set; }
}