[RB] Newbie warning !! A few questions

[Charles Yeomans]

On Monday, August 25, 2003, at 06:13 AM, Jan Erik Moström wrote:

> Hi
>
> Once every 6 months or so I start learning using Valentina and every
> time something happens so I have to wait another 6 months 8-) Well, 
> it's
> time again and I need to clarify a few things. I'm making a simple
> database with 6 related tables in order to learn Valentina for future
> use.
>
>
> If I create a database and add a baseobject (class 'P') that represents
> people then this represents the whole table, right?
>
> If I want to treat a person as an object (and have several such objects
> available at the same time ... no, not a listing but for editing) then 
> I
> need to create another class 'RealPerson'. When I need an instance of
> 'RealPerson' I should request if from 'P' (who either creates a new
> record or return an existing depending on the situtation), right?
>
> If I need to save the changes to a 'RealPerson' object, then I should
> call 'P' with this object as a parameter, right? ('P' looks up which
> record needs updateing and updates it)
>
> To do this, I need some way to uniqely identify the person in the 'P'
> table using some data in the 'RealPerson' object. Should I assign a
> unique identifier myself or is this one use for the VObjectPtr/RecID?

Use the recID value.

In general, what I have is an abstract PersistentObject class that has 
a function ID() as Integer, and subroutines Retrieve(theID as Integer) 
and Save() (and other methods, of course).  Internally there is a 
protected property recID as Integer.  I have two events 
MapCursorToObject(c as VCursor) and MapObjectToCursor(c as VCursor) 
that I implement in subclasses.  Here's some code.

Charles Yeomans

Sub Retrieve(theID as Integer)
   Const methodName = "Retrieve"

   dim c as VCursor
   dim db as VDataBase
   dim bo as boPersistentClass
   dim query as DBQuery

   If me.IsNull then
     Return
   End if

   bo = boPersistentClass(me.manager.baseObject)
   db = bo.DataBase

   query = app.DB.NewQuery
   query.AddAllFields bo
   query.AddTable bo
   query.WhereCondition = new WHERENodeEquals(bo.RecID, theID)
   query.ReadOnly = true
   c = query.Cursor
   If c.FirstRecord then
     me.recID = theID
     me.lastUpdate = c.DoubleField(bo.lastChanged.name).value
     me.pHasBeenDeleted = c.BooleanField(bo.HasBeenDeleted.name).value
     MapCursorToObject c
   End if
   Retrieved //new event
   c = nil

Exception oops
   LogException oops, me.ClassName, methodName
End Sub


Sub Save()
   Const methodName = "Save"

   dim db as VDataBase
   dim bo as boPersistentClass
   dim query as DBQuery
   dim c as VCursor
   dim d as Date

   If me.IsNull then
     Return
   End if

   bo = me.manager.baseObject
   db = bo.DataBase

   If me.recID = 0 then
     me.Create
   End if
   Saving //new event --provides a hook for setting object properties

   query = app.DB.NewQuery
   query.ReadOnly = false
   query.AddAllFields bo
   query.AddTable bo
   query.WhereCondition = new WHERENodeEquals(bo.RecID, me.recID)
   c = query.Cursor
   MapObjectToCursor c
   d = new Date
   c.DoubleField(bo.lastChanged.name).value = d.TotalSeconds
   c.BooleanField(bo.HasBeenDeleted.name).value = me.ToBeDeleted
   me.pHasBeenDeleted = me.ToBeDeleted
   If c.Update then
     bo.Flush
     Saved //new event -- provides a hook for saving associated objects
     me.Manager.AnnounceUpdate me
     c = nil
   Else
     Raise new ValentinaException(db)
   End if

Exception oops
   LogException oops,  me.ClassName, methodName
End Sub