Custom Classes

[Keith Wilby]

I've been trying to get my head around custom classes by following the
example in the Visual Basic Language Developer's Handbook by Sybex. I think
I have a handle on what they're about, albeit a fragile one at the moment.
Having said that, I can't think of a single application for one so obviously
I need educating further. Does anyone have any practical examples of custom
classes and their application that might help me broaden my horizons?

Many thanks.

Keith.

[Albert D. Kallal]

>

"when I create and set the myTour = "tour id", then all of the recordsets
for bus company, hotels, rates etc gets loaded into the object."

Could you just expand a little on this please? How does the data get
loaded, do you open a recordset in a subroutine? Still missing the point
here I think!

Yes, in code I could go

dim tour1 as new clsrides
dim tour2 as new clsRides

tour1.TourID = 123 ' load tour 123
tour2.TourID = 34 'load tour 34

At this point, I have TWO tours loaded in ram, and thus go

msgbox "hotel for tour 123 is " & Tour1.HotelName

msgbox "hotel for tour 34 is" & Tour2.HotelName

So, note how the above was VERY little coding, and I can have TWO tours in
memory at the SAME time. And, even if I just need one in code...it is still
much easer then a bunch of subroutines and global variables that would trip
over them selves....

The class object is over 600 lines of code in total.....

Additional properties of the class object are outlined here:
http://www.members.shaw.ca/AlbertKal...Appendex4.html

The left side does NOT display all properties, but gives you an idea.....
the actual code in the class object for TourID is:

Public Property Let TourId(LoadID As Long)

' Loads/setsup the tour object (pricing etc..)
' DO NOT load if id is same as passed....

Dim myDB As Database
Dim qryBusList As QueryDef

Set myDB = DBEngine(0)(0)

If m_TourId <0 Then
' tour is loaded, check for same tour...
If m_TourId = LoadID Then

' tour already loaded...don't re-load
Exit Property

End If
End If

m_TourId = LoadID

' loads the load rates....

Set m_rstTour = myDB.OpenRecord set("select * from tbltours where id = " &
m_TourId)

With m_rstTour
If .RecordCount 0 Then

m_FromDate = !FromDate
m_Todate = !ToDate
m_HotelId = !Hotel
m_dtDepositDue = m_FromDate - !DaysDue

' load up hotel informaton
Set m_rstHotel = myDB.OpenRecord set("select * from tblHotels where
id = " & m_rstTour!Hotel )

' load up buses attachted to this tour
Set qryBusList = myDB.QueryDefs( "qryTourBusList B")
qryBusList.Para meters(0) = m_TourId
Set m_rstBusList = qryBusList.Open Recordset

' load up seasonal pricing talbes
Call TLoadRates

' set tax tax.
If m_rstTour!NoGst = True Then
m_GstRate = 0
Else
m_GstRate = gblGst(m_FromDa te)
m_PstRate = gblPst(m_FromDa te)
End If

Else
m_TourId = 0
End If
End With

End Property

--
Albert D. Kallal (Access MVP)
Edmonton, Alberta Canada
pl************* ****@msn.com

[Albert D. Kallal]

By the way, that appendix link where I outline that access class object is

is part of larger article here:

http://www.members.shaw.ca/AlbertKal...000000003.html

In that article, I explain why I used class objects in ms-access....

--
Albert D. Kallal (Access MVP)
Edmonton, Alberta Canada
pl************* ****@msn.com

[Keith Wilby]

"Albert D. Kallal" <Pl************ *******@msn.com wrote in message
news:%Ooch.4118 71$R63.320926@p d7urf1no...

By the way, that appendix link where I outline that access class object is

is part of larger article here:

http://www.members.shaw.ca/AlbertKal...000000003.html

In that article, I explain why I used class objects in ms-access....

--
Albert D. Kallal (Access MVP)
Edmonton, Alberta Canada
pl************* ****@msn.com

Many thanks Albert (and Gord), I shall read though all of this today.

Regards,
Keith.

[Keith Wilby]

"Albert D. Kallal" <Pl************ *******@msn.com wrote in message
news:GGoch.4118 63$R63.146206@p d7urf1no...

tour1.TourID = 123 ' load tour 123
tour2.TourID = 34 'load tour 34

At this point, I have TWO tours loaded in ram, and thus go

msgbox "hotel for tour 123 is " & Tour1.HotelName

msgbox "hotel for tour 34 is" & Tour2.HotelName

<snip>

>
the actual code in the class object for TourID is:

Public Property Let TourId(LoadID As Long)

Albert,

Dumb question: how do you supply the argument to the property? You have
"tour1.Tour ID = 123" but wouldn't you get an "argument not optional" error
there?

Thanks for your patience, I'll get the hang of this yet!

Keith.

[Gord]

Keith Wilby wrote:

"Albert D. Kallal" <Pl************ *******@msn.com wrote in message
news:GGoch.4118 63$R63.146206@p d7urf1no...

>

tour1.TourID = 123 ' load tour 123
tour2.TourID = 34 'load tour 34

At this point, I have TWO tours loaded in ram, and thus go

msgbox "hotel for tour 123 is " & Tour1.HotelName

msgbox "hotel for tour 34 is" & Tour2.HotelName

<snip>

the actual code in the class object for TourID is:

Public Property Let TourId(LoadID As Long)

Albert,

Dumb question: how do you supply the argument to the property? You have
"tour1.Tour ID = 123" but wouldn't you get an "argument not optional" error
there?

Property Let statements behave differently than Function and Sub
statements do. 123 *is* the argument.

[Keith Wilby]

"Gord" <gd*@kingston.n etwrote in message
news:11******** **************@ l12g2000cwl.goo glegroups.com.. .

>

>>
Dumb question: how do you supply the argument to the property? You have
"tour1.TourI D = 123" but wouldn't you get an "argument not optional"
error
there?

Property Let statements behave differently than Function and Sub
statements do. 123 *is* the argument.

Thanks for your patience Gord. Another dumb question but hopefully the
answer will make the penny drop. In a simple example, if I have a table
"tblHoliday s" with fields "ID" and "Country" and I have a class
"clsHoliday ", how do I set and retrieve a "Country" property? I'm calling
the class using:

Dim hlHoliday As clsHoliday
Set hlHoliday = New clsHoliday
hlHoliday.HolID = "ABC123"

Here's the class code:

Property Let HolID(strID As String)

Dim db As DAO.Database, rs As DAO.Recordset
Dim strCountry As String
Set db = CurrentDb
Set rs = db.OpenRecordse t("Select * from tblHolidays Where ID = '" & strID &
"'")
With rs
If .RecordCount 0 Then
'*** What goes here to get the other properties? ***
End If
End With

rs.Close
Set rs = Nothing
db.Close
Set db = Nothing

End Property

[Gord]

Keith Wilby wrote:

"Gord" <gd*@kingston.n etwrote in message
news:11******** **************@ l12g2000cwl.goo glegroups.com.. .

>
Dumb question: how do you supply the argument to the property? You have
"tour1.Tour ID = 123" but wouldn't you get an "argument not optional"
error
there?

Property Let statements behave differently than Function and Sub
statements do. 123 *is* the argument.

Thanks for your patience Gord. Another dumb question but hopefully the
answer will make the penny drop. In a simple example, if I have a table
"tblHoliday s" with fields "ID" and "Country" and I have a class
"clsHoliday ", how do I set and retrieve a "Country" property? I'm calling
the class using:

Dim hlHoliday As clsHoliday
Set hlHoliday = New clsHoliday
hlHoliday.HolID = "ABC123"

Here's the class code:

Property Let HolID(strID As String)

Dim db As DAO.Database, rs As DAO.Recordset
Dim strCountry As String
Set db = CurrentDb
Set rs = db.OpenRecordse t("Select * from tblHolidays Where ID = '" & strID &
"'")
With rs
If .RecordCount 0 Then
'*** What goes here to get the other properties? ***
End If
End With

rs.Close
Set rs = Nothing
db.Close
Set db = Nothing

End Property

Hi, Keith. Try this:

'-----start of class module----
Option Compare Database
Option Explicit

Private mstrHolID As String
Private mstrCountry As String

Public Property Get HolID() As String
' return the property value
HolID = mstrHolID
End Property

Public Property Let HolID(ByVal strID As String)
Dim db As DAO.Database, rs As DAO.Recordset

' save the ID property value
mstrHolID = strID

' retrieve other attributes
Set db = CurrentDb
Set rs = db.OpenRecordse t( _
"Select * from tblHolidays Where ID = '" & strID & "'")
With rs
If .RecordCount 0 Then
'*** What goes here to get the other properties? ***
mstrCountry = rs!Country
End If
End With

rs.Close
Set rs = Nothing
db.Close
Set db = Nothing

End Property

Public Property Get Country() As String
' return the property value
Country = mstrCountry
End Property
'-----end of class module----
'-----start of usage example----
Sub HolidayTest()
Dim hlHoliday As clsHoliday

Set hlHoliday = New clsHoliday
hlHoliday.HolID = "ABC123"
Debug.Print hlHoliday.Count ry

Set hlHoliday = Nothing
End Sub
'-----end of usage example----

[Keith Wilby]

"Gord" <gd*@kingston.n etwrote in message
news:11******** **************@ n67g2000cwd.goo glegroups.com.. .

>
Hi, Keith. Try this:

<snip>

Duh, I feel so stupid now ;-) The penny has finally dropped, for this
example at least. Many thanks again Gord.

Keith.