Enhanced Guide to Oracle8i

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Enhanced Guide to Oracle8i
Chapter 7 Creating Custom Forms
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Data Block and Custom Forms

• Data block form
• Based on data blocks that are associated with
  specific database tables
• Reflect the structure of the database
• Custom form
• Based on control blocks that process data from
  multiple tables
• Reflect business processes rather than the
  database structure

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Creating a Custom Form

• Create the form
• Create the form window and canvas manually
• Create a control block
• Data block that is not associated with a specific
  table
• Contains form items that you manually draw on the
  canvas
• Create form triggers to process data

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Form Triggers

• Code that is associated with a form object and an
  event
• Can contain SQL INSERT, UPDATE, DELETE, and
  SELECT commands
• Referencing form text item values in triggers
• block_name.item_name

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Program Units

• Self-contained programs
• Can be called from PL/SQL triggers
• Used to make triggers more modular, and reuse
  code within triggers

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Referencing System Date and Time Values in Forms
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Using the Forms Debugger to Find Runtime Errors

• Run the form using the Run Form Debug button
• Set a breakpoint on the program line where you
  want to start examining variable values during
  execution

Breakpoint
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Using the Forms Debugger to Find Runtime Errors
3. Run the program and execute the trigger
containing the breakpoint 4. Single-step through
the code and monitor the variable values
Execution arrow
Variable values
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Forms Debugger Variable Types

• Module (block)
• Current values of form items
• Stack
• Values of local variables declared in PL/SQL
  triggers or program units
• Global
• Values of global variables used in form triggers
  or program units

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Strategy for Using the Forms Debugger

• Single-step through the trigger and identify the
  program line causing the error
• Run the form again and single-step through the
  trigger, and note the values of variables just
  before the line containing the error executes
• Determine the cause of the error

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Form Triggers

• Categories
• Block processing
• Interface event
• Master-detail processing
• Message handling
• Navigational
• Query time
• Transactional
• Validation

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Trigger Timing

• PRE-
• Fires just before associated event occurs
• POST-
• Fires just after associated event occurs
• ON-, WHEN-, KEY-
• Fires immediately, in response to specific user
  actions, such as key presses

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Trigger Scope

• Defines where an event must occur to make the
  trigger fire
• Trigger scope includes the object to which the
  trigger is attached, as well as all objects
  within that object
• Form-level fires when event occurs within any
  block or item in the form
• Block-level fires when event occurs within any
  item in the form
• Item-level fires only when event occurs within
  that item

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Trigger Execution Hierarchy

• If 2 related objects have the same trigger, the
  higher-level objects trigger fires first
• Form block, forms trigger fires first
• Block item, blocks trigger fires first
• You can specify a custom execution order on the
  trigger Property Palette

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Navigational Triggers

• External navigation occurs when user causes
  form focus to change
• Internal navigation occurs as a result of
  internal form triggers that fire in response to
  external navigation events

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Triggers That Fire at Form Startup
Result on User Screen Display
Triggers Fired
User Action
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2
1
Form appears, but with no data visible
PRE-FORM PRE-BLOCK
User starts form
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5
WHEN-NEW-FORM-INSTANCE WHEN-NEW-BLOCK-INSTANCE WHE
N-NEW-RECORD-INSTANCE WHEN-NEW-ITEM-INSTANCE
Form is available for use
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Triggers That Fire as a Result Of External
Navigation
Result on User Screen Display
Triggers Fired
User Action
User places the insertion point in a text item
Insertion point appears in item
WHEN-NEW-ITEM-INSTANCE
User clicks the Next Record button
Next record appears
WHEN-NEW-RECORD-INSTANCE WHEN-NEW-ITEM-INSTANCE
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Triggers That Fire When a Form Closes
Result on User Screen Display
User Action
Triggers Fired
User closes the Forms Runtime window
Forms Runtime window closes
POST-BLOCK POST-FORM
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Directing External Navigation

• Form tab order is based on item order in Object
  Navigator block list

Form tab order
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Moving to a Specific Form Item

• GO_ITEM(block_name_item_name)

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Oracle Error Message Severity Levels

• 5 informative message
• 10 informative message advising user of
  procedural error
• 20 condition that keeps trigger from working
  correctly
• 25 condition that keeps form from working
  correctly
• gt25 extreme severity

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Suppressing Lower Level System Messages

• Set SYSTEM.MESSAGE_LEVEL variable to a higher
  level in PRE-FORM trigger
• SYSTEM.MESSAGE_LEVEL 25

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Providing User Feedback in Forms

• Message
• Text in message line at bottom of form
• Informational only user doesn't have to respond
• Alert
• Dialog box
• Allows user to choose different ways to proceed

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Messages

• Syntax
• MESSAGE(message text)

Message
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Alerts

• Form-level object
• Object properties define alert appearance

Message
Title
Style icon
Buttons
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Code for Displaying an Alert

• DECLARE
• alert_button NUMBER
• BEGIN
• alert_button SHOW_ALERT('alert_name')
• IF alert_button ALERT_BUTTON1 THEN
• program statements for first button
• ELSE
• program statements for second button
• END IF
• END

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Avoiding User Errors

• Make primary and foreign key text items
  non-navigable
• When user moves form focus to primary or foreign
  key text item, trigger moves focus to alternate
  form item

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Trapping Runtime Errors

• Create an ON-ERROR event trigger
• Form-level trigger
• Executes whenever an FRM- or ORA- error occurs
• -FRM errors generated by Forms Runtime
• -ORA errors generated by database

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Form Procedures That Return System Error
Information

• DBMS_ERROR_CODE -ORA error code
• DBMS_ERROR_TEXT -ORA error message
• ERROR_CODE -FRM error code
• ERROR_TEXT -FRM error message
• MESSAGE_CODE most recent error code (either
  ORA or FRM)
• MESSAGE_TEXT most recent error message (either
  ORA or FRM)

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Structure of ON-ERROR Trigger

• BEGIN
• --trap FRM errors
• IF ERROR_CODE FRM_error_code1 THEN
• error handler
• ELSIF ERROR_CODE FRM_error_code2 THEN
• error handler
• ELSE
• --trap ORA errors
• IF DBMS_ERROR_CODE -ORA_error_code1 THEN
• error handler
• ELSIF DBMS_ERROR_CODE -ORA_error_code2 THEN
• error handler
• END IF
• END IF
• END

Code to trap FRM errors
Code to trap ORA errors
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Form Validation

• Ensures that form data meets preset requirements
  so erroneous data is not sent to database
• Validation unit specifies the largest data
  chunk that the user can enter enter before
  validation occurs
• Can be performed at the form, block, record, or
  item level
• Specified in the Validation Unit property on the
  form Property Palette

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Types of Form Validation

• Data
• Specifies data types, lengths, and maximum and
  minimum values
• Database
• Specifies which operations a user can perform on
  a text item
• List of Values
• Specifies whether a data value must be validated
  against the text items LOV

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Data Blocks vs. Control Blocks

• Data block
• Easy to create and use
• Is associated with a single table, and reflects
  the tables structure
• Control block
• Requires a lot of custom programming
• Can contain items from many different tables
• You can link data and control blocks to take
  advantages of the strengths of each

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Linking Data Blocks and Control Blocks

• Create the control block as the master block
• Create the data block as the detail block, but do
  not create a master-detail relationship
• Create a master-detail relationship manually in
  the WHERE Clause property of the detail block
• data_block_field control_block.text_item

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Displaying and Refreshing the Data Block Values

• Create a trigger to
• Place the insertion point in the data block
• GO_BLOCK(block_name)
• Flush the data block to make its data consistent
  with the master block and the database
• EXECUTE_QUERY

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Converting a Data Block to a Control Block

• Create a data block and layout that contains most
  of the required text items
• Convert the data block to a control block by
  changing the following block properties
• Database Data Block No
• Required No

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Creating a Form with Multiple Canvases

• Users should be able to see all canvas text items
  without scrolling
• For complex applications with many text items,
  divide application into multiple canvases

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Block Navigation Order

• First block in Object Navigator Data Blocks list
  determines block items that first appear when
  form opens
• Users can use the Tab key to navigate among
  different block items
• Canvas that contains block items automatically
  appears

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Block Navigation Order
Block order
Canvas order doesnt matter
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Controlling Block Navigation

• Block Navigation Style property
• Same Record navigation cycles through items on
  same block
• Change Data Block navigation moves to next data
  block in list

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Tab Canvases

• Multiple-page canvases that allow users to move
  among different canvas surfaces by clicking tabs

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Tab Canvas Components

• Tab canvas
• Collection of related tab pages
• Tab pages
• Surfaces that display form items
• Tab labels
• Identifier at top of tab page
• A tab canvas lies on top of a content canvas

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Creating a Tab Canvas

• Use the Tab Canvas tool on the Layout
  Editor tool palette to draw a tab canvas on an
  existing content canvas
• By default, a new tab canvas has 2 tab pages
• Create new tab pages as needed
• Adjust tab page properties

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Important Tab Page Properties
Name how the page Is referenced in the form
Label Caption that appears on the associated
tab
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Adjusting the Tab Page Order

• Tab page that appears first is tab page whose
  block items appear first in the Object Navigator

Block order
Tab page order doesnt matter
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Stacked Canvases

• Canvas that appears on an existing content
  canvas, and can be displayed or hidden as needed
• Allows user to configure canvas items

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Stacked Canvas Example
Content canvas
Stacked canvas
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Creating a Stacked Canvas

• Use the Stacked Canvas tool on the Layout Editor
  tool palette to draw a stacked canvas on an
  existing content canvas
• Create block items on the stacked canvas
• Create buttons and triggers to display and hide
  the stacked canvas

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Displaying and Hiding a Stacked Canvas

• Displaying a stacked canvas
• GO_BLOCK(stacked_canvas_block)
• SHOW_VIEW(stacked_canvas)
• Hiding a stacked canvas
• GO_BLOCK(stacked_canvas_block)
• HIDE_VIEW(stacked_canvas)