传递ObjectContext EF 4.0

Question

我有两个类Queries和ContactRepository。

    public static class Queries
    {
        public static Contact GetContactByName(CEntities context, string name)
        {
            return (from Contact c in context.Contacts
                    where c.Name == name
                    select c).FirstOrDefault();
        }
    }

    public class ContactRepository
    {
        private CEntities _dbContext;

        public ContactRepository()
        {
            _dbContext = new CEntities();
        }

        public void CreateContactAddress(string contactName, string address, string city, string state, string zip)
        {
            int contactId;
            ContactAddress ca = new ContactAddress();

            contactId = Queries.GetContactByName(_dbContext, contactName).Id;

            ca.ContactId = contactId;
            ca.Address = address
            ca.City = city;
            ca.State = state;
            ca.Zip = zip;

            _dbContext.ContactAddresses.AddObject(ca);
            _dbContext.SaveChanges();
        }
    }

当我调用CreateContactAddress（）时，SaveChanges（）方法崩溃并出现以下错误：

  

无法确定有效的订购   对于从属操作。依赖   由于外键可能存在   约束，模型要求或   存储生成的值。

我可以将LINQ查询移动到CreateContactAddress（）方法本身，一切都很完美。谁能解释一下发生了什么？