保存时未将集合属性正确添加到父项

看看下面的代码示例。

它的作用：

1. 它吸引了一群客户。如果它已经知道该客户，它将检索该客户的现有数据库对象（这是问题重重的部分）。否则，它将创建一个新对象（这很好）
2. 所有与社会保障号码匹配（CPR）的贷款都将添加到新客户或现有客户中

问题是：它适用于新客户对象，但当我检索现有客户对象时，贷款在保存时会失去与客户的关系（CustomerID=null）。它们仍然保存到数据库中。

有什么想法吗？

protected void BuildCustomerData()
{
    Console.WriteLine("  Starting the customer build.");
    var counter = 0;
    var recycleCount = 100;
    var reportingCount = 100;
    var sTime = DateTime.Now;
    var q = from c in db.IntermediaryRkos
            select c.CPR;
    var distincts = q.Distinct().ToArray();
    var numbersToProcess = distincts.Count();
    Console.WriteLine("  Identified " + numbersToProcess + " customers. " + (DateTime.Now - sTime).TotalSeconds);
    foreach (var item in distincts)
    {
        var loans = from c in db.IntermediaryRkos
                    where c.CPR == item
                    select c;
        var existing = db.Customers.Where(x => x.CPR == item).FirstOrDefault();
        if (existing != null)
        {
            this.GenerateLoanListFor(existing, loans);
            db.Entry(existing).State = System.Data.EntityState.Modified;
        }
        else
        {
            var customer = new Customer
            {
                CPR = item,
            };
            this.GenerateLoanListFor(customer, loans);
            db.Customers.Add(customer);
            db.Entry(customer).State = System.Data.EntityState.Added;
        }
        counter++;
        if (counter % recycleCount == 0)
        {
            this.SaveAndRecycleContext();
        }
        if (counter % reportingCount == 0)
        {
            Console.WriteLine("    Processed " + counter + " customers of " + numbersToProcess + ".");
        }
    }
    db.SaveChanges();
}
protected void GenerateLoanListFor(Customer customer, IQueryable<IntermediaryRko> loans)
{
    customer.Loans = new List<Loan>();
    foreach (var item in loans.Where(x => x.DebtPrefix == "SomeCategory").ToList())
    {
        var transformed = StudentLoanMap.CreateFrom(item);
        customer.Loans.Add(transformed);
        db.Entry(transformed).State = System.Data.EntityState.Added;
    }
}

编辑1:

如前所述，我正在手动设置状态。这是由于RecycleContext调用，该调用是为了最大限度地提高数据库事务性能而实现的：

protected void SaveAndRecycleContext()
{
    db.SaveChanges();
    db.Dispose();
    db = new SolutionDatabase();
    db.Configuration.AutoDetectChangesEnabled = false;
    db.Configuration.ValidateOnSaveEnabled = false;
}