Storing a vb class object in a data base?

[lm]

It is possible to store an entire class object in a database field (long
binary?). I'm looking for a way to store all private and public data, I
guess like a "retreivable memory snapshot" or something. It would work
something like this:

Dim objOriginal as new clsObject
Dim objNew as Object
Dim Index as Integer

SaveToDataBase Index, objOriginal
Set objOriginal = Nothing

Set objNew = ReadFromDataBase(Index)

objNew should now have the same contents as objOriginal had.
Does enybody have any suggestions or ideas how something similar could be
accomplished.

Thanks
Lars B.

[Eric Litwin]

"lm" <xwx@ix.netcom.com> wrote:
>It is possible to store an entire class object in a database field (long
>binary?). I'm looking for a way to store all private and public data, I
>guess like a "retreivable memory snapshot" or something. It would work
>something like this:
>
>Dim objOriginal as new clsObject
>Dim objNew as Object
>Dim Index as Integer
>
>SaveToDataBase Index, objOriginal
>Set objOriginal = Nothing
>
>Set objNew = ReadFromDataBase(Index)
>
>objNew should now have the same contents as objOriginal had.
>Does enybody have any suggestions or ideas how something similar could be
>accomplished.
>
>Thanks
>Lars B.
>
>

You need to serialize your object state when you save it to the database
and de-serialize it when you retrieve it.

Serializing/de-serializing is a complex subject and there are many ways you
could approach it.

The easiest way would be to use a PropertyBag object and write each member
variable (property) in your object to the PropertyBag. You can then serialize
the PropertyBag to a byte array (using the Contents function) and save that
byte array as a string to your database.

You could then read that string back from the database, set it as the contents
of a new PropertyBag object, and then read each Property and assign it to
your member variables.

For example - a simple Employee object:

Option Explicit

Private mlngId As Long
Private mstrName As String
Private mcurSalary As Currency

' Temporary database - just use a local string for demo purposes
Private mDatabase As String

Public Sub WriteToDatabase()
Dim propBag As New PropertyBag
Dim Buffer As String

propBag.WriteProperty "Name", mstrName
propBag.WriteProperty "Salary", mcurSalary

Buffer = propBag.Contents

' Code to save the Buffer to database goes here
mDatabase = Buffer
End Sub

Public Sub ReadFromDatabase(Id As Long)
Dim propBag As New PropertyBag
Dim strBuffer As String
Dim arBuffer() As Byte

' Read from Database using Id and assign to strBuffer
strBuffer = mDatabase

' Read the string into a byte array
arBuffer = strBuffer

propBag.Contents = arBuffer

' Set our properties
mlngId = Id
mstrName = propBag.ReadProperty("Name", "")
mcurSalary = propBag.ReadProperty("Salary", 0)
End Sub