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
我有同样的问题，当我试图修改目标实体的标量属性，并意识到我不小心引用了目标实体的父:
entity.GetDbContextFromEntity().Entry(entity).Reference(i => i.ParentEntity).Query().Where(p => p.ID == 1).Load();
只是一个建议，确保目标实体不引用任何父对象。
其他回答
如果你正在使用自动绘图器，面临以下问题是一个很好的解决方案，它为我工作
https://www.codeproject.com/Articles/576393/Solutionplusto-aplus-Theplusoperationplusfailed
因为问题是我们正在映射空导航属性，我们实际上不需要在实体上更新它们，因为它们在契约上没有改变，我们需要在映射定义上忽略它们:
ForMember(dest => dest.RefundType, opt => opt.Ignore())
所以我的代码是这样的:
Mapper.CreateMap<MyDataContract, MyEntity>
ForMember(dest => dest.NavigationProperty1, opt => opt.Ignore())
ForMember(dest => dest.NavigationProperty2, opt => opt.Ignore())
.IgnoreAllNonExisting();
我也遇到了同样的问题，但我知道它在其他情况下也能正常工作，所以我把问题简化为:
parent.OtherRelatedItems.Clear(); //this worked OK on SaveChanges() - items were being deleted from DB
parent.ProblematicItems.Clear(); // this was causing the mentioned exception on SaveChanges()
OtherRelatedItems有一个复合主键(parentId +一些本地列)，工作正常 probleaticitems有自己的单列主键，而parentId只是一个FK。这导致了Clear()之后的异常。
我所要做的就是使ParentId成为复合PK的一部分，以表明没有父元素就不能存在子元素。我使用DB-first模型，添加PK并将parentId列标记为EntityKey(因此，我必须在DB和EF中更新它-不确定EF单独是否足够)。
仔细想想，这是一个非常优雅的区别，EF使用它来决定没有父对象的子对象是否“有意义”(在这种情况下，Clear()不会删除它们并抛出异常，除非你将ParentId设置为其他/特殊的对象)，或者-就像最初的问题一样-我们期望项一旦从父对象中删除就会删除。
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。
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);
你必须手动清除ChildItems集合，并在其中添加新项目:
thisParent.ChildItems.Clear();
thisParent.ChildItems.AddRange(modifiedParent.ChildItems);
之后，您可以调用DeleteOrphans扩展方法，它将处理孤立的实体(它必须在DetectChanges和SaveChanges方法之间调用)。
public static class DbContextExtensions
{
private static readonly ConcurrentDictionary< EntityType, ReadOnlyDictionary< string, NavigationProperty>> s_navPropMappings = new ConcurrentDictionary< EntityType, ReadOnlyDictionary< string, NavigationProperty>>();
public static void DeleteOrphans( this DbContext source )
{
var context = ((IObjectContextAdapter)source).ObjectContext;
foreach (var entry in context.ObjectStateManager.GetObjectStateEntries(EntityState.Modified))
{
var entityType = entry.EntitySet.ElementType as EntityType;
if (entityType == null)
continue;
var navPropMap = s_navPropMappings.GetOrAdd(entityType, CreateNavigationPropertyMap);
var props = entry.GetModifiedProperties().ToArray();
foreach (var prop in props)
{
NavigationProperty navProp;
if (!navPropMap.TryGetValue(prop, out navProp))
continue;
var related = entry.RelationshipManager.GetRelatedEnd(navProp.RelationshipType.FullName, navProp.ToEndMember.Name);
var enumerator = related.GetEnumerator();
if (enumerator.MoveNext() && enumerator.Current != null)
continue;
entry.Delete();
break;
}
}
}
private static ReadOnlyDictionary<string, NavigationProperty> CreateNavigationPropertyMap( EntityType type )
{
var result = type.NavigationProperties
.Where(v => v.FromEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many)
.Where(v => v.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.One || (v.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.ZeroOrOne && v.FromEndMember.GetEntityType() == v.ToEndMember.GetEntityType()))
.Select(v => new { NavigationProperty = v, DependentProperties = v.GetDependentProperties().Take(2).ToArray() })
.Where(v => v.DependentProperties.Length == 1)
.ToDictionary(v => v.DependentProperties[0].Name, v => v.NavigationProperty);
return new ReadOnlyDictionary<string, NavigationProperty>(result);
}
}
