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; }
}

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。

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; }
}

我在几个小时前遇到过这个问题，并尝试了所有方法，但在我的情况下，解决方案与上面列出的不同。

如果你使用已经从数据库检索实体，并试图修改它的孩子的错误将发生，但如果你从数据库获得实体的新副本，不应该有任何问题。 不要用这个:

 public void CheckUsersCount(CompanyProduct companyProduct) 
 {
     companyProduct.Name = "Test";
 }

用这个:

 public void CheckUsersCount(Guid companyProductId)
 {
      CompanyProduct companyProduct = CompanyProductManager.Get(companyProductId);
      companyProduct.Name = "Test";
 }

出现这个问题是因为我们试图删除父表，但仍然存在子表数据。 我们利用级联删除来解决这个问题。

在模型中创建dbcontext类中的方法。

 modelBuilder.Entity<Job>()
                .HasMany<JobSportsMapping>(C => C.JobSportsMappings)
                .WithRequired(C => C.Job)
                .HasForeignKey(C => C.JobId).WillCascadeOnDelete(true);
            modelBuilder.Entity<Sport>()
                .HasMany<JobSportsMapping>(C => C.JobSportsMappings)
                  .WithRequired(C => C.Sport)
                  .HasForeignKey(C => C.SportId).WillCascadeOnDelete(true);

之后，在我们的API调用中

var JobList = Context.Job                       
          .Include(x => x.JobSportsMappings)                                     .ToList();
Context.Job.RemoveRange(JobList);
Context.SaveChanges();

级联删除选项删除父表以及与父相关的子表，使用这个简单的代码。用这个简单的方法试试。

删除范围用于删除数据库中的记录列表 谢谢