IA 345 What Every PowerBuilder Developer Needs to Know about DropDown DataWindows

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IA 345What Every PowerBuilder DeveloperNeeds to
Know aboutDropDown DataWindows
Tom Bartha Principal Consultant PricewaterhouseCoo
pers tom.bartha_at_us.pwcglobal.com
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Objectives of this Session

• To explore what is inherent in a DDDW versus what
  a PowerBuilder developer has to provide.
• To demonstrate basic and developer provided
  functionality.
• To provide a full text version of this
  presentation.
• All code examples will be available on the
  Presenters Web Page www.sybase.com/techwave2000/p
  resenters

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Before DropDown DataWindows

• Regardless of ever increasing computing resources
  at an ever decreasing cost, we need to store some
  data in codified manner.
• To display full data value corresponding to coded
  information we often resort to drop-down lists.
• Drop-down lists representing constantly changing
  data needs to be dynamically populated.
• Prior to PowerBuilder 3.0 this required work.

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Before PowerBuilder 3.0

• In order to populate a ddlb with data from a
  table, we had to
• Declare a cursor
• Open the cursor
• Fetch the data into the code table of the ddlb
  one at a time
• In the open event of the window (parent of ddlb)
  you would have the following script

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Code Example for Cursor

• integer li_counter
• string Is_state_id, Is_state_name
• DECLARE state_cursor CURSOR FOR
• Select state_id, state_name
• From states_table
• Using SQLCA
• OPEN state_cursor
• (continued)

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Code Example for Cursor (continued)

• Do WHILE sqlca.sqlcode 0
• Fetch state_cursor INTO Is_state_id,
• Is_state_name
• IF sqlca.sqlcode 0 THEN
• ddlb_data.SetValue("state", li_counter,
• Is_state_name "-t"
• string(Is_state_id))
• END IF
• li_counter
• LOOP
• Close state_cursor

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DropDown DataWindow Definitions

• Definitions in Help and the On-line Books
• A DataWindowChild object is a nested report or a
  DropDown DataWindow within a DataWindow object.
  For example, a DataWindow object that populates a
  column having the DropDownDataWindow edit style
  is a DataWindowChild object.

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DropDown DataWindow Definitions (continued)

• Definitions in Help and the On-line Books
• A DataWindowChild object is used for accessing
  DataWindow objects independently from DataWindow
  functionality, and it inherits from the system
  Structure object because it needs storage and
  autoinstantiation.
• A DataWindowChild object has no properties and
  no events, but it does have functions.

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Use of DropDown DataWindows

• 1. Data Entry

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Use of DropDown DataWindows

• 2. Data Display and Reports

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Use of DropDown DataWindows

• 3. Search DataWindows

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Creating a DropDown DataWindow

• Define a datawindow object
• Nest this datawindow object inside a parent
  datawindow
• Build another datawindow as parent
• OR
• Use an exisiting multi-column datawindow as parent

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Exclusive DropDown DataWindows

• Option A
• Create a new datawindow object using the same
  table as the one the dddw is defined on.
• Option B
• Create a new free-form external datawindow
  object.
• Option C
• Use recursion, namely, place the dddw inside
  itself.

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Exclusive DropDown DataWindows (continued)

• Demonstration

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Populating DropDown DataWindows

• Default Process
• Parent Managing the Child
• Multiple dddws in Parent
• Frequently Used dddw Result Sets
• Infrequently Used dddw Result Sets

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DDDW Retrieval Arguments

• DDDW may or may not have retrieval arguments
• If not programmed you get the retrieval argument
  dialog window

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DDDWs with Retrieval Arguments

• PowerBuilder will attempt to Retrieve a DDDW if
  the DDDW has no rows in the Primary Buffer
• Overriding the Default Process
• Preload a blank row
• Retrieve the DDDW before the main DW
• Using Retrieval Arguments
• Retrieve dddw when window opens
• Retrieve dddw when something changes

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Storing Data in a DataWindow Object

• Rows Data in DW Painter
• Data are stored with the DW
• Data are automatically displayed in the
  DataWindow when it is instantiated

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Child DataWindows

• A child datawindow is any datawindow which is
  nested inside another datawindow and, therefore,
  dependent on its parent.
• The child does not have a name accessible at the
  window level.
• We must define a variable of type datawindowchild
  and trap the childs handle.
• Use GetChild function
• dw_control.GetChild(col_name, child_handle)

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Overriding the Default Process

• A child datawindow works in very close
  conjunction with its parent
• The child picks up the parents transaction
  object.
• The child will retrieve its result set from the
  database when the parent is retrieved.
• To override these defaults we must remember that
  as long as the child datawindow has a valid
  result set, no new result set will be retrieved
  by default.

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Overriding the Default Process (continued)

• Script in the open event of the window
• integer li_return
• datawindowchild ldwx_dept
• dw_parent.SetTransObject(sqlca)
• // Obtain the handle of the dddw in the
  department column
• li_return dw_parent.GetChild(dept_id,
  ldwc_dept)
• IF li_return 1 THEN
• ldwc_dept.SetTransObject(sqlca)
• ldwc_dept.InsertRow(0)
• dw_parent.Retrieve( )

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Overriding the Default Process (continued)

• ELSE
• MessageBox(DataWindow Error, Unable to obtain
  dddw handle.)
• END IF

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Sharing Hidden DDDWs

• Create a non-visual object.
• Define an instance array of DataStores.
• Add a method to share data.
• Call the method to share from the DataWindows
  that need caching.
• After sharing dddws retrieve your DataWindows in
  a normal way.

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Infrequently Used DDDW Result Sets

• Problem On the parent datawindow there are a
  number of dddw columns, each of which contains a
  large number of rows. Not all the result sets
  are needed at the same time or even in one user
  session.
• Want to avoid the retrieval time, unless result
  set is needed.
• Solution Populate the dddws only if the user
  clicks on the corresponding columns.
• (see demonstration)

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Code Examples

• Synchronized DDDWs
• Retrieve Arguments vs Filtering
• Adding data elements to a dddw on the fly
• Cascading dddws

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Slide title, may be two lines, Arial Black, 32
pt.
Color Palette
Arrow Style
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Slide title, may be two lines, Arial Black, 32
pt.