Adding new rows throws 'Multiplicity constraint violated' - entity-framework

Question

I have two related classes like these :
public partial class WorkItem
{
public WorkItem()
{
this.ChildWorkItems = new HashSet<WorkItem>();
this.Attachments = new HashSet<Attachment>();
}
public int Id { get; set; }
public Nullable<int> ParentId { get; set; }
public string Title { get; set; }
public string SenderUserName { get; set; }
public virtual ICollection<WorkItem> ChildWorkItems { get; set; }
public virtual WorkItem ParentWorkItem { get; set; }
public virtual ICollection<Attachment> Attachments { get; set; }
}
and the realted 1-n attachments :
public partial class Attachment
{
public int Id { get; set; }
public string Filename { get; set; }
public Nullable<int> WorkItemId { get; set; }
public virtual WorkItem WorkItem { get; set; }
}
Now I want to insert some new workitems with their attachment into the database. I use the following code for insertion :
at first put all workitems (regardless of their attachments )
var workItems = new List<WorkItem>();
foreach (var username in AllUsers)
{
var workitem = new WorkItem();
//fill the simple fields
lst.Add(workitem);
Context.WorkItems.Add(workitem);
}
then set the attachments :
foreach (var fileName in MYFILES)
{
var file = new System.IO.FileInfo(fileName);
foreach (var workItem in workItems)
{
var att =
new Attachment()
{
Filename = file.Name,
};
context.Attachments.Add(att);
att.WorkItem = workItem;
}
}
But I get the following exception :
Multiplicity constraint violated. The role 'WorkItem' of the relationship 'AienCRMModel.FK_WorkItemAttachments_WorkItems' has multiplicity 1 or 0..1.
The interesting point is if I only have One workitem , everything is ok. If I have more than one WorkItem with no attachments , again everything is ok. The problem raises when having more than one WorkItem with at least one attachment.
I read lots of other post but nothing usefuk was found.
NOTE :
I use EF Code-First 4.3 with a T4 template which generate my classes from the EDMX file.
I Really appreciate your helps in advance.
EDIT
I Attached the full EDMX diagram of mentioned tables here :
EDIT 2
Complete .edmx file at here : http://www.4shared.com/file/zQUO_qk7/CrmModel141.html?

Answer 1

Somewhere in your code you are using the same object instance for different rows in the database like this (just an example):
var o1 = new O1Class();
foreach (var o2 in collection)
{
o2.O1s.Add(o1);
}
But is have to be:
foreach (var o2 in collection)
{
o2.O1s.Add(new O1Class());
}
I this example O1Class can have only one O2Class in their relationship but the Entity Framework keep the reference on the o1 instance so when you adding it to multiple O2Class instances the EF will think that the current O1Class has multiple O2Class instances which is incorrect.