CByteArrayFile - storing objects in databases using DAO

Daniel Kaminski

4.42/5 (6 votes)

Mar 18, 2000

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A class used to serialize object into a database field

You HongJiang contributed the CByteArrayFile class and article, and Daniel Kaminski contributed the demonstration application.

In my project I need to serialize some objects into a database field with DAO. However, I can not find any support for serializing anobject into database field. I had to implemented one by myself.

In this example, I will show you a class named CByteArrayFile. It is a derived class of CMemFile. With this class we can serialize objects into a CByteArray object. We can then use DFX_Binary to transfer data into a database "long binary" field.

Following is the sample code of how to use the CByteArrayFile class.

In the class which need to be serialized (such as CSomeClass):

CSomeClass::TransferDataWithByteArray(CByteArray& byteArray, BOOL bStore)
{
   CByteArrayFile byFile;
   byFile.SetArray(&byteArray);    // attach byteArray with byFile
   
   if (bStore) // store object into byteArray
   {
      // create CArchive object with CByteArray File
      CArchive ar( &byFile, CArchive::store);
 
      // Call CSomeClass::Serialize function
      Serialize(ar);

      ar.Close();
   }
   else // load object from byteArray
   {
     CArchive ar( &byFile, CArchive::load);
     Serialize(ar);    // Call CSomeClass::Serialize function
     ar.Close();
   }
 
  // important!! detach byteArray with byFile. Or byteArray will be 
  // free with byFile
  byFile.Detach();
}

In the file which used CDaoRecordset derived a class such as CSomeDaoRecordset

CSomeDaoRecordset rs;    // rs.m_byteLongField is a CByteArray class
CSomeClass object;

// 1. Write to record
rs.Open(. . .);
rs.AddNew();
object.TransferDataWithByteArray(rs.m_byteLongField, TRUE /* store */);
. . .
rs.Update();
rs.Close();

// 2. Read from record
rs.Open(. . .);
object.TransferDataWithByteArray(rs.m_byteLongField, FALSE /* load */);
...

rs.Close();