[Задача] >---------< [Документ] +-------+< [Файл]

INSERT INTO DOCUMENTS ... -- все поля и их корректные значения
INSERT INTO FILES ... -- все поля и их корректные значения
ERROR: Could not synchronize database state with session

public int AddDocumentWithFile(Document document, HttpPostedFileBase data)
        {
            Document targetDocument = new Document();
            targetDocument.DOC_ACTUAL = document.DOC_ACTUAL;
 ...
            DbFileRepository fileRepository = new DbFileRepository(_session);
            ITransaction transaction = _session.BeginTransaction();
            try
            {
                GenericDAOImpl<Document>.Save(targetDocument, _session);
                fileRepository.AddFile(targetDocument, data);
                transaction.Commit();
            }
            catch (Exception ex)
            {
                transaction.Rollback();
                throw new Exception(ex.Message);
            }
            return targetDocument.DOC_ID;
        }

        public int AddFile(Document document, HttpPostedFileBase data)
        {
            DbFile targetFile = new DbFile();
            targetFile.FILE_NAME = Path.GetFileName(data.FileName);
            targetFile.FILE_EXTENTION = Path.GetExtension(data.FileName);
            targetFile.FILE_DATE_CREATION = DateTime.Now;
            targetFile.FILE_VERSION = 1;
            targetFile.FILE_MIME_TYPE = data.ContentType;
            targetFile.FILE_SIZE = data.ContentLength;
            targetFile.FILE_BODY = new byte[data.ContentLength];
            targetFile.Document = document;
            targetFile.Employee = document.Employee;
            data.InputStream.Read(targetFile.FILE_BODY, 0, data.ContentLength);

            GenericDAOImpl<DbFile>.Save(targetFile, _session);

            return targetFile.FILE_ID;
        }

public static class GenericDAOImpl<TEntity>
    {
...
        public static TEntity Save(TEntity entity, ISession session)
        {
            if (!session.Transaction.IsActive)
            {
                using (var tx = session.BeginTransaction())
                {
                    session.SaveOrUpdate(entity);
                    tx.Commit();
                }
            }
            else
            {
                session.SaveOrUpdate(entity);
            }
            return entity;
        }
    }

doc.DOC_ID
doc.DOC_ACTUAL
file.FILE_BODY
file.FILE_MIME_TYPE
file.FILE_ID
...

doc.DocumentId, doc.Actual, file.FileBody, file.MimeType, file.FileId