Data control <-> Data objects 
Author Message
 Data control <-> Data objects


to consider need of ressources and efficiency in the design of a
VB 4.0 (Enterpr.Ed.) + database application (tables with up to
500.000 datasets) we urgently need clarification concerning
"interaction" between data controls and data objects.

1. Assign data control-database and recordset to data objects:
   (Data1 is a data control on a form with an open database/recordset)

   set Db = Data1.Database
   set Rs = Data1.Recordset

   Does this mean that
   a) there is only one database/recordset object and both, Db/Rs
      as well as Data1, refer to the same objects, or that
   b) there are separate independent objects for Db/Rs and Data1,
      respectively ??

2. Assign data object (open recordset) to data control:

   set Db = OpenDatabase ("MyDb")
   set Rs = OpenRecordset ("MyTable")
   'According to online-help/"database property" it is not
   'allowed to set Data1.database = Db
   set Data1.Recordset = Rs

   The Data1 control can be used sucessfully afterwards e.g. with bound
   controls even if no databasename has been set for Data1 in advance.
   Besides the corresponding questions 1a/b: Which database object is now
   referenced by Data1 ? Does it get a copy of Db ?

3. Synchronize ?
   Online help/"Recordset Property" states that data controls can be used
   on a MDI parent form and assigned to data controls on MDI child forms
   thus "synchronizing" all the child forms and their bound controls with
   the parent. Testing this with a simple example has not made clear
   what is meant by "synchronizing". And again, is there only one database
   and recordset object (that of the MDI parent data control) or separate
   ones for each childs when using set data1child.recordset = data1mdi.recordset ?

4. General strategy ?
   What is "your" general strategy for the cooperation between data controls
   for the user interface and data objects in code when using large datasets ?
   Is there a possibility to roughly estimate the amount of memory space
   needed for a recordset object (e.g. a tabletype recordset with 100.000 datasets)?
   Or can we trust VB and the jet engine to be efficient and economical so that
   we finally do not have to take care about the problems stated above or the
   number of data objects, instances etc. ?

Thanks in advance,

 Dr. Johann Broethaler

 Institute of Public Finance         Tel.  +43 1/58801-4317
 and Infrastructure Policy, E267     Fax   +43 1/5042738

 Karlsgasse 11                                      \\|//
 A-1040 Vienna                                      (o o)
 Austria                             -----------oOOo-(_)-oOOo----------

Mon, 25 Jan 1999 03:00:00 GMT  
 [ 1 post ] 

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