我得到这个错误时，我GetById()在一个实体，然后设置子实体的集合到我的新列表，来自MVC视图。
操作失败 关系是无法改变的 因为一个或多个外键 Properties是非空的。当一个 关系发生了变化 相关外键属性设置为 空值。如果外键是 不支持空值，新建 关系必须被定义 必须分配外键属性 另一个非空值或 必须删除不相关的对象。
我不太理解这句话:
这种关系无法改变 因为一个或多个外键 Properties是非空的。
我为什么要改变两个实体之间的关系?它应该在整个应用程序的生命周期内保持不变。
发生异常的代码只是简单地将集合中修改过的子类分配给现有的父类。这将有望满足取消子类，增加新的和修改。我本以为实体框架处理这个。
代码行可以提炼为:
var thisParent = _repo.GetById(1);
thisParent.ChildItems = modifiedParent.ChildItems();
_repo.Save();
当前回答
我尝试过这些方法和其他方法，但没有一个很有效。由于这是谷歌上的第一个答案，我将在这里添加我的解。
对我来说很有效的方法是在提交期间将关系排除在外，这样EF就不会搞砸了。我通过在DBContext中重新找到父对象并删除它来做到这一点。因为重新找到的对象的导航属性都是空的，所以在提交过程中会忽略子对象的关系。
var toDelete = db.Parents.Find(parentObject.ID);
db.Parents.Remove(toDelete);
db.SaveChanges();
注意，这里假设外键设置为ON DELETE CASCADE，所以当父行被删除时，子行将被数据库清除。
其他回答
使用slaa的解决方案，我创建了一些通用函数来帮助更新子对象和子对象的集合。
我的所有持久对象都实现了这个接口
/// <summary>
/// Base interface for all persisted entries
/// </summary>
public interface IBase
{
/// <summary>
/// The Id
/// </summary>
int Id { get; set; }
}
这样我就在我的存储库中实现了这两个函数
/// <summary>
/// Check if orgEntry is set update it's values, otherwise add it
/// </summary>
/// <param name="set">The collection</param>
/// <param name="entry">The entry</param>
/// <param name="orgEntry">The original entry found in the database (can be <code>null</code> is this is a new entry)</param>
/// <returns>The added or updated entry</returns>
public T AddOrUpdateEntry<T>(DbSet<T> set, T entry, T orgEntry) where T : class, IBase
{
if (entry.Id == 0 || orgEntry == null)
{
entry.Id = 0;
return set.Add(entry);
}
else
{
Context.Entry(orgEntry).CurrentValues.SetValues(entry);
return orgEntry;
}
}
/// <summary>
/// check if each entry of the new list was in the orginal list, if found, update it, if not found add it
/// all entries found in the orignal list that are not in the new list are removed
/// </summary>
/// <typeparam name="T">The type of entry</typeparam>
/// <param name="set">The database set</param>
/// <param name="newList">The new list</param>
/// <param name="orgList">The original list</param>
public void AddOrUpdateCollection<T>(DbSet<T> set, ICollection<T> newList, ICollection<T> orgList) where T : class, IBase
{
// attach or update all entries in the new list
foreach (T entry in newList)
{
// Find out if we had the entry already in the list
var orgEntry = orgList.SingleOrDefault(e => e.Id != 0 && e.Id == entry.Id);
AddOrUpdateEntry(set, entry, orgEntry);
}
// Remove all entries from the original list that are no longer in the new list
foreach (T orgEntry in orgList.Where(e => e.Id != 0).ToList())
{
if (!newList.Any(e => e.Id == orgEntry.Id))
{
set.Remove(orgEntry);
}
}
}
要使用它，我做以下工作:
var originalParent = _dbContext.ParentItems
.Where(p => p.Id == parent.Id)
.Include(p => p.ChildItems)
.Include(p => p.ChildItems2)
.SingleOrDefault();
// Add the parent (including collections) to the context or update it's values (except the collections)
originalParent = AddOrUpdateEntry(_dbContext.ParentItems, parent, originalParent);
// Update each collection
AddOrUpdateCollection(_dbContext.ChildItems, parent.ChildItems, orgiginalParent.ChildItems);
AddOrUpdateCollection(_dbContext.ChildItems2, parent.ChildItems2, orgiginalParent.ChildItems2);
希望这能有所帮助
额外:你也可以创建一个单独的DbContextExtentions(或者你自己的context inferface)类:
public static void DbContextExtentions {
/// <summary>
/// Check if orgEntry is set update it's values, otherwise add it
/// </summary>
/// <param name="_dbContext">The context object</param>
/// <param name="set">The collection</param>
/// <param name="entry">The entry</param>
/// <param name="orgEntry">The original entry found in the database (can be <code>null</code> is this is a new entry)</param>
/// <returns>The added or updated entry</returns>
public static T AddOrUpdateEntry<T>(this DbContext _dbContext, DbSet<T> set, T entry, T orgEntry) where T : class, IBase
{
if (entry.IsNew || orgEntry == null) // New or not found in context
{
entry.Id = 0;
return set.Add(entry);
}
else
{
_dbContext.Entry(orgEntry).CurrentValues.SetValues(entry);
return orgEntry;
}
}
/// <summary>
/// check if each entry of the new list was in the orginal list, if found, update it, if not found add it
/// all entries found in the orignal list that are not in the new list are removed
/// </summary>
/// <typeparam name="T">The type of entry</typeparam>
/// <param name="_dbContext">The context object</param>
/// <param name="set">The database set</param>
/// <param name="newList">The new list</param>
/// <param name="orgList">The original list</param>
public static void AddOrUpdateCollection<T>(this DbContext _dbContext, DbSet<T> set, ICollection<T> newList, ICollection<T> orgList) where T : class, IBase
{
// attach or update all entries in the new list
foreach (T entry in newList)
{
// Find out if we had the entry already in the list
var orgEntry = orgList.SingleOrDefault(e => e.Id != 0 && e.Id == entry.Id);
AddOrUpdateEntry(_dbContext, set, entry, orgEntry);
}
// Remove all entries from the original list that are no longer in the new list
foreach (T orgEntry in orgList.Where(e => e.Id != 0).ToList())
{
if (!newList.Any(e => e.Id == orgEntry.Id))
{
set.Remove(orgEntry);
}
}
}
}
像这样使用它:
var originalParent = _dbContext.ParentItems
.Where(p => p.Id == parent.Id)
.Include(p => p.ChildItems)
.Include(p => p.ChildItems2)
.SingleOrDefault();
// Add the parent (including collections) to the context or update it's values (except the collections)
originalParent = _dbContext.AddOrUpdateEntry(_dbContext.ParentItems, parent, originalParent);
// Update each collection
_dbContext.AddOrUpdateCollection(_dbContext.ChildItems, parent.ChildItems, orgiginalParent.ChildItems);
_dbContext.AddOrUpdateCollection(_dbContext.ChildItems2, parent.ChildItems2, orgiginalParent.ChildItems2);
我今天遇到了这个问题，想分享我的解决方案。在我的例子中，解决方案是在从数据库中获取Parent之前删除Child项。
以前我是这样做的代码如下。然后我将得到这个问题中列出的相同错误。
var Parent = GetParent(parentId);
var children = Parent.Children;
foreach (var c in children )
{
Context.Children.Remove(c);
}
Context.SaveChanges();
对我来说，有效的方法是先获取子项，使用parentId(外键)，然后删除这些项。然后我可以从数据库中获取父元素，在这一点上，它应该不再有任何子元素，我可以添加新的子元素。
var children = GetChildren(parentId);
foreach (var c in children )
{
Context.Children.Remove(c);
}
Context.SaveChanges();
var Parent = GetParent(parentId);
Parent.Children = //assign new entities/items here
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。
我尝试过这些方法和其他方法，但没有一个很有效。由于这是谷歌上的第一个答案，我将在这里添加我的解。
对我来说很有效的方法是在提交期间将关系排除在外，这样EF就不会搞砸了。我通过在DBContext中重新找到父对象并删除它来做到这一点。因为重新找到的对象的导航属性都是空的，所以在提交过程中会忽略子对象的关系。
var toDelete = db.Parents.Find(parentObject.ID);
db.Parents.Remove(toDelete);
db.SaveChanges();
注意，这里假设外键设置为ON DELETE CASCADE，所以当父行被删除时，子行将被数据库清除。
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。
