EF4 Code First Adding a Entity with virtual navigation property null to a 1 to many

I have the following EF4 Code First classes:

[Serializable]
pu开发者_StackOverflow社区blic class WOChangeLogHeader
{
    [Key]
    public int WOChangeLogHeaderId { get; set; }
    public DateTime tadded { get; set; }

    public virtual WorkOrderHeader WO { get; set; }
    public int WorkOrderHeaderId { get; set; }

    [MaxLength(50)]
    public string chng_type { get; set; }
    [MaxLength(50)]
    public string chng_process { get; set; }

    public int chng_by { get; set; }

    public virtual ICollection<WOChangeLog> ChangeLogRecords {get;set;}

}

[Serializable]
public class WOChangeLog
{
    [Key]
    public int WOChangeLogId { get; set; }
    public DateTime tadded { get; set; }

    public virtual WOChangeLogHeader ChangeLogHeader { get; set; }
    public int WOChangeLogHeaderId { get; set; }

    [MaxLength(50)]
    public string chng_field { get; set; }
    public string old_value { get; set; }
    public string new_value { get; set; }

}

And setup the addition of a new WoChangeLogHeader like so:

    private void addWOChangeLogRecord(string chgField, string oldVal, string newVal, WorkOrderHeader wo)
    {


        WOChangeLog log = new WOChangeLog();
        log.chng_field = chgField.Trim();
        log.old_value = oldVal == null ? "-NULL VALUE-" : oldVal.Trim();
        log.new_value = newVal == null ? "-NULL VALUE-" : newVal.Trim();
        log.tadded = DateTime.Now;


        if (CurrentWOChangeLogHeader == null)
        {

            CurrentWOChangeLogHeader = new WOChangeLogHeader();
            CurrentWOChangeLogHeader.WO = wo;
            CurrentWOChangeLogHeader.WorkOrderHeaderId = wo.WorkOrderHeaderId;
            CurrentWOChangeLogHeader.chng_by = -2;
            CurrentWOChangeLogHeader.chng_process = "WindowsService";
            CurrentWOChangeLogHeader.chng_type = "Auto-Update";
            CurrentWOChangeLogHeader.tadded = DateTime.Now;

        }

        CurrentWOChangeLogHeader.ChangeLogRecords.Add(log);  // Error here

    }

However at this point ChangeLogRecords navigation property is null so I get a null object reference error...

But if I try to add the WOChangeLogHeader without adding any children, so that I can subsequently reference it like so:

 WOChangeLog log = new WOChangeLog();
 log.chng_field = chgField.Trim();
 log.old_value = oldVal == null ? "-NULL VALUE-" : oldVal.Trim();
 log.new_value = newVal == null ? "-NULL VALUE-" : newVal.Trim();
 log.tadded = DateTime.Now;
 log.ChangeLogHeader = CurrentWOChangeLogHeader;

then I get the following error ?

The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted.

It will not let me SaveChanges on the Context when the ChangeLogRecords is null either...

How to add a new Entity that is the parent in a 1 to many relationship like this ?

Thanks Greg

The problem may be here:

public virtual WOChangeLogHeader ChangeLogHeader { get; set; } 
public int WOChangeLogHeaderId { get; set; } 

Both of these lines make a reference to the header, but only the first line is needed.

Try removing the second line.