Tuesday, July 7, 2009

Types of Triggers in Forms

1. Types of Triggers in Forms

Block-processing triggers: - Block processing triggers fire in response to events related to record management in a block. E.g. When-Create-Record, When-Clear-Block, When-Database-Record, When-Remove-Record

Interface event triggers: - Interface event triggers fire in response to events that occur in the form interface. Some of these triggers, such as When-Button-Pressed, fire only in response to operator input or manipulation. Others, like When-Window-Activated, can fire in response to both operator input and programmatic control. E.g. When-Button-Pressed, When-Checkbox-Changed, Key- [all], When-Radio-Changed, When-Timer-Expired, When-Window-Activated, When-Window-Resized

Master-detail triggers: - Form Builder generates master-detail triggers automatically when you define a master-detail relation between blocks. The default master-detail triggers enforce coordination between records in a detail block and the master record in a master block. Unless you are developing your own custom block-coordination scheme, you do not need to define these triggers yourself. Instead, simply create a relation object, and let Form Builder generate the triggers required to manage coordination between the master and detail blocks in the relation. E.g. On-Check-Delete-Master, On-Clear-Details, On-Populate-Details

Message-handling triggers: - Form Builder automatically issues appropriate error and informational messages in response to runtime events. Message handling triggers fire in response to these default messaging events. E.g. On-Error, On-Message

Navigational triggers: - Navigational triggers fire in response to navigational events. For instance, when the operator clicks on a text item in another block, navigational events occur as Form Builder moves the input focus from the current item to the target item. Navigational events occur at different levels of the Form Builder object hierarchy (Form, Block, Record, Item). Navigational triggers can be further sub-divided into two categories: Pre- and Post- triggers, and When-New-Instance triggers. Pre- and Post- triggers fire as Form Builder navigates internally through different levels of the object hierarchy. As you might expect, these triggers fire in response to navigation initiated by an operator, such as pressing the [Next Item] key. However, be aware that these triggers also fire in response to internal navigation that Form Builder performs during default processing. To avoid unexpected results, you must consider such internal navigation when you use these triggers. E.g. Pre-Form, Pre-Block, Pre-Text-Item, Post-Text-Item, Post-Record, Post-Block, Post-Form
When-New-Instance triggers fire at the end of a navigational sequence that places the input focus in a different item. Specifically, these triggers fire just after Form Builder moves the input focus to a different item, when the form returns to a quiet state to wait for operator input. Unlike the Pre- and Post- navigational triggers, the When-New-Instance triggers do not fire in response to internal navigational events that occur during default form processing. E.g. When-New-Form-Instance, When-New-Block-Instance, When-New-Record-Instance, When-New-Item-Instance

Query-time triggers: - Query-time triggers fire just before and just after the operator or the application executes a query in a block. E.g. Pre-Query, Post-Query

Transactional triggers: - Transactional triggers fire in response to a wide variety of events that occur as a form interacts with the data source. E.g. On-Delete, On-Insert, On-Lock, On-Logon, On-Update, Post-Database-Commit, Post-Delete, Post-Forms-Commit, Post-Insert, Post-Update, Pre-Commit, Pre-Delete, Pre-Insert, Pre-Update

Validation triggers: - Validation triggers fire when Form Builder validates data in an item or record. Form Builder performs validation checks during navigation that occurs in response to operator input, programmatic control, or default processing, such as a Commit operation. E.g. When-Validate-Item, When-Validate-Record

2. Sequence of Trigger Fire while Committing

Ø KEY Commit
Ø Pre Commit
Ø Pre/On/Post Delete
Ø Pre/On/Post Update
Ø Pre/On/Post Insert
Ø On commit
Ø Post Database Commit

3. Master-Detail Relation (Triggers/Procedures/Properties)

On-Check-Delete-Master: - Fires when Form Builder attempts to delete a record
in a block that is a master block in a master-detail relation.
On-Clear-Details: - Fires when Form Builder needs to clear records in a block
that is a detail block in a master-detail relation because those records no longer
correspond to the current record in the master block.
On-Populate-Details: - Fires when Form Builder needs to fetch records into a block that is the detail block in a master-detail relation so that detail records are synchronized with the current record in the master block.
(i) Isolated: - Masters Can be deleted when Child is existing
Triggers: - On Populate details Block
On Clear Details Form
Procedure
Check Package Failure
Clear all master Detail
Query Master Detail
(ii) Non- Isolated: - Masters Cannot be deleted when Child is existing.
Triggers: - On Populate details Block
On Check Delete master Block
On Clear Details Form
Procedure
Check Package Failure
Clear all master Detail
Query Master Detail
(iii) Cascading: - Child Record Automatically Deleted when Masters is deleted.
Triggers: - On Populate details Block
Pre Delete Block
On Clear Details Form
Procedure
Check Package Failure
Clear all master Detail
Query Master Detail

4. Dynamically create LOV/List Item

You can also add list elements individually at runtime by using the ADD_LIST_ELEMENT built-in subprogram, or you can populate the list from a record group at runtime using the POPULATE_LIST built-in. If you populate the list from a record group, be sure that the record group you are using to populate the list contains the relevant values before you call POPULATE_LIST. If the record group is a static record group, it will already contain the appropriate values. Otherwise, you should populate the group at runtime using one of the record group subprograms.

5. Object Libraries (Use/Benefits)

The Object Library provides an easy method of reusing objects and enforcing standards across the entire development organization.
Object Library can be used to:

1. Create, store, maintain, and distribute standard and reusable objects.
2. Rapidly create applications by dragging and dropping predefined objects to your form.

There are several advantages to using object libraries to develop applications:

1. Object libraries are automatically re-opened when you startup Form Builder, making your reusable objects immediately accessible.
2. You can associate multiple object libraries with an application. For example, you can create an object library specifically for corporate standards, and you can create an object library to satisfy project-specific requirements.
3. Object libraries feature Smart Classes-- objects that you define as being the standard. You use Smart Classes to convert objects to standard objects.

6. Key-next/Post-Text (Difference)

Post-Text–Item: Fires during the Leave the Item process for a text item. Specifically, this trigger fires when the input focus moves from a text item to any other item.

Key-Next-Item: The key-next is fired as a result of the key action. Key next will not fire unless there is a key event.

7. Call From/New Form/Open Form (Difference)

Call Form: Runs an indicated form while keeping the parent form active. Form Builder runs the called form with the same Runform preferences as the parent form. When the called form is exited Form Builder processing resumes in the calling form at the point from which you initiated the call to CALL_FORM.
PROCEDURE CALL_FORM (formmodule_name VARCHAR2, display NUMBER, switch_menu NUMBER, query_mode NUMBER, data_mode NUMBER, paramlist_name/id VARCHAR2);

New Form: Exits the current form and enters the indicated form. The calling form is terminated as the parent form. If the calling form had been called by a higher form, Form Builder keeps the higher call active and treats it as a call to the new form. Form Builder releases memory (such as database cursors) that the terminated form was using.
Form Builder runs the new form with the same Runform options as the parent form. If the parent form was a called form, Form Builder runs the new form with the same options as the parent form.
PROCEDURE NEW_FORM (formmodule_name VARCHAR2, rollback_mode NUMBER, query_mode NUMBER, data_mode NUMBER, paramlist_name/id VARCHAR2);

Open Form: Opens the indicated form. Use OPEN_FORM to create multiple-form applications, that is, applications that open more than one form at the same time.
PROCEDURE OPEN_FORM (form_name VARCHAR2, activate_mode NUMBER, session_mode NUMBER, data_mode NUMBER, paramlist_id/name PARAMLIST);

8. Types of Canvases (Stacked/Content Difference)

(i) Content Canvas (Default Canvas) [A content canvas is the required on each window you create]
(ii) Stack Canvas [you can display more then one stack canvas in a window at the same time]
(iii) Tab Type Window [In Tab canvas that have tab pages and have one or more then tab page]
(iv) Toolbar Canvas [A toolbar canvas often is used to create Toolbar Windows. There are two type of Toolbar window.
a. Horizontal Toolbar Canvas: - Horizontal Toolbar canvases are displayed at the top of the window, Just Under the Main Menu Bar.
b. Vertical Toolbar Canvas: - While vertical Toolbar are displayed along the Left Edge of the window.

9. Object Groups (Use)

An object group is a container for a group of objects. You define an object group when you want to package related objects so you can copy or subclass them in another module.
Object groups provide a way to bundle objects into higher-level building blocks that can be used in other parts of an application and in subsequent development projects. For example, you might build an appointment scheduler in a form and then decide to make it available from other forms in your applications. The scheduler would probably be built from several types of objects, including a window and canvas, blocks, and items that display dates and appointments, and triggers that contain the logic for scheduling and other functionality. If you packaged these objects into an object group, you could then copy them to any number of other forms in one simple operation.
You can create object groups in form and menu modules. Once you create an object group, you can add and remove objects to it as desired.

10. Various Block Co-ordination Properties

The various Block Coordination Properties are
a) Immediate
Default Setting. The Detail records are shown when the Master Record are shown.
b) Deffered with Auto Query
Oracle Forms defer fetching the detail records until the operator navigates to the detail block.
c) Deferred with No Auto Query
The operator must navigate to the detail block and explicitly execute a query




11. How to attach same LOV to multiple items

We can use the same LOV for 2 columns by passing the return values in global values and using the global values in the code.

12. Report Level Triggers (Sequence)

· Before parameter form
· After parameter form
· Before Report
· Between Pages
· After Report

13. Static & Dynamic LOV

The static LOV contains the predetermined values while the dynamic LOV contains values that come at run time

14. Format Triggers (What are they)

A format trigger is a PL/SQL function executed before an object is formatted. A trigger can be used to dynamically change the formatting attributes of the object.

15. Flex & Confine Mode in Reports
Confine mode:
a. Switched on by default; change via View® View Options® Layout...
b. It prevents operations which would cause a report not to work e.g. moving a field outside its parent repeating frame
Flex mode:
Moves the object it’s enclosing objects and objects in their push path simultaneously to maintain the same overall relationship in the report. E.g. if you try to move a field outside its repeating frame, the Repeating Frame will grow to accommodate the field and so will any objects around the repeating frame.
Only one object can be moved/resized at one time in flex mode - if you try more than one only one whose control point is clicked on will be done, the other objects will be de-selected.
Objects can be moved/resized horizontally or vertically; not diagonally.
16. Matrix Reports (Matrix By Groups)

A matrix (cross tab) report contains one row of labels, one column of labels, and information in a grid format that is related to the row and column labels. A distinguishing feature of matrix reports is that the number of columns is not known until the data is fetched from the database.
To create a matrix report, you need at least four groups: one group must be a cross-product group, two of the groups must be within the cross-product group to furnish the "labels," and at least one group must provide the information to fill the cells. The groups can belong to a single query or to multiple queries.

A matrix with group report is a group above report with a separate matrix for each value of the master group.

A nested matrix (crosstab) report is a matrix report in which at least one parent/child relationship appears within the matrix grid.
The new Child Dimension property of the nested group enables you to eliminate empty rows and/or columns in your single-query nested matrix.

Types of Matrix Reports
Simple Matrix Report:
Is a matrix with only two dimensions

Nested Matrix Report: Has multiple dimensions going across and/or down the page
Multi-Query Matrix with Break: Is similar to a nested matrix report in that it has more than two dimensions. Does not display records that do not contain data
Matrix Break Reports: Contains a new matrix for each master record


17. Lexical & Bind Parameters in Reports

Lexical Parameters: Lexical references are placeholders for text that you embed in a SELECT statement. You can use lexical references to replace the clauses appearing after SELECT, FROM, WHERE, GROUP BY, ORDER BY, HAVING, CONNECT BY, and START WITH.
You cannot make lexical references in a PL/SQL statement. You can, however, use a bind reference in PL/SQL to set the value of a parameter that is then referenced lexically in SQL. Look at the example below.
You create a lexical reference by entering an ampersand (&) followed immediately by the column or parameter name. A default definition is not provided for lexical references. Therefore, you must do the following:
Ø Before you create your query, define a column or parameter in the data model for each lexical reference in the query. For columns, you must enter Value if Null, and, for parameters, you must enter Initial Value. Report Builder uses these values to validate a query with a lexical reference.
Ø Create your query containing lexical references.

Bind Parameters: Bind references (or bind variables) are used to replace a single value in SQL or PL/SQL, such as a character string, number, or date. Specifically, bind references may be used to replace expressions in SELECT, WHERE, GROUP BY, ORDER BY, HAVING, CONNECT BY, and START WITH clauses of queries. Bind references may not be referenced in FROM clauses or in place of reserved words or clauses.
You create a bind reference by entering a colon (:) followed immediately by the column or parameter name. If you do not create a column or parameter before making a bind reference to it in a SELECT statement, Report Builder will create a parameter for you by default.

18. Column Mode Property in Reports

The Column Mode property controls how Report Builder fetches and formats data for instances of repeating frames. With Column Mode set to Yes, the next instance of a repeating frame can begin formatting before the previous instance is completed. With Column Mode set to No, the next instance cannot begin formatting before the previous instance is completed. Column Mode is used mainly for master repeating frames or repeating frames that contain fields that may expand vertically or horizontally (i.e., elasticity is Variable or Expand).

19. Diff b/w Package Spec & Body

Packages provide a method of encapsulating and storing related procedures, funtions and other package constructs as a unit in the database. They offer increased functionality (for example, global package variables can be declared and used by any procedure in the package). They also improve performance (for example, all objects of the package are parsed, compiled, and loaded into memory once).
Package specification contains declarations of public constructs where as the package body contains definitions of all those public constructs and declarations & definitions of private constructs.

20. P/L SQL Tables / Arrays

PL/SQL tables are declared in the declaration portion of the block. A table is a composite datatype in PL/SQL. PL/SQL tables can have one column and a primary key neither of which can be named. The column can be any scalar type but primary key should be a BINARY_INTEGER datatype.
Rules for PL/SQL Tables:
1. A loop must be used to insert values into a PL/SQL Table
2. You cannot use the Delete command to delete the contents of PL/SQL Table. You must assign an empty table to the PL/SQL table being deleted.



21. Various Cursor Attributes

SQL%ROWCOUNT: Number of rows affected by most recent SQL statement.
SQL%FOUND: Boolean attribute that evaluates to TRUE if most recent SQL statement affects one or more rows.
SQL%NOTFOUND: Boolean attribute that evaluates to TRUE if most recent SQL statement does not affect any row.
SQL%ISOPEN: Always evaluates to FALSE because P/L SQL closes implicit cursors immediately after they are executed.

22. Different Database Triggers

Database triggers are PL/SQL, Java, or C procedures that run implicitly whenever a table or view is modified or when some user actions or database system actions occur. Database triggers can be used in a variety of ways for managing your database. For example, they can automate data generation, audit data modifications, enforce complex integrity constraints, and customize complex security authorizations.
Row Triggers
A row trigger is fired each time the table is affected by the triggering statement.
For example, if an UPDATE statement updates multiple rows of a table, a row trigger is fired once for each row affected by the UPDATE statement.
If a triggering statement affects no rows, a row trigger is not executed at all.
Row triggers are useful if the code in the trigger action depends on data provided by the triggering statement or rows that are affected.
Statement Triggers
A statement trigger is fired once on behalf of the triggering statement, regardless of the number of rows in the table that the triggering statement affects (even if no rows are affected).
For example, if a DELETE statement deletes several rows from a table, a statement-level DELETE trigger is fired only once, regardless of how many rows are deleted from the table.
Statement triggers are useful if the code in the trigger action does not depend on the data provided by the triggering statement or the rows affected.
For example, if a trigger makes a complex security check on the current time or user, or if a trigger generates a single audit record based on the type of triggering statement, a statement trigger is used.

BEFORE vs. AFTER Triggers
When defining a trigger, you can specify the trigger timing.
That is, you can specify whether the trigger action is to be executed before or after the triggering statement.
BEFORE and AFTER apply to both statement and row triggers.
BEFORE Triggers BEFORE triggers execute the trigger action before the triggering statement. This type of trigger is commonly used in the following situations:
BEFORE triggers are used when the trigger action should determine whether the triggering statement should be allowed to complete. By using a BEFORE trigger for this purpose, you can eliminate unnecessary processing of the triggering statement and its eventual rollback in cases where an exception is raised in the trigger action.
BEFORE triggers are used to derive specific column values before completing a triggering INSERT or UPDATE statement.

AFTER Triggers AFTER triggers execute the trigger action after the triggering statement is executed. AFTER triggers are used in the following situations:
AFTER triggers are used when you want the triggering statement to complete before executing the trigger action.
If a BEFORE trigger is already present, an AFTER trigger can perform different actions on the same triggering statement.

Combinations
Using the options listed in the previous two sections, you can create four types of triggers:
BEFORE statement trigger Before executing the triggering statement, the trigger action is executed.
BEFORE row trigger Before modifying each row affected by the triggering statement and before checking appropriate integrity constraints, the trigger action is executed provided that the trigger restriction was not violated.
AFTER statement trigger After executing the triggering statement and applying any deferred integrity constraints, the trigger action is executed.
AFTER row trigger After modifying each row affected by the triggering statement and possibly applying appropriate integrity constraints, the trigger action is executed for the current row provided the trigger restriction was not violated. Unlike BEFORE row triggers, AFTER row triggers lock rows.

New Database Triggers
Startup, Shutdown, Logon, Logoff, Alter, Create, Drop

23. List Item Types

Poplist: The poplist style list item appears initially as a single field (similar to a text item field). When the end user selects the list icon, a list of available choices appears.
Tlist: The Tlist style list item appears as a rectangular box, which displays a fixed number of values. When the Tlist contains values that cannot be displayed (due to the displayable area of the item), a vertical scroll bar appears, allowing the end user to view and select undisplayed values.
Combo Box: The combo box style list item combines the features found in poplists and text items. It displays fixed values and can accept a user-entered value.

7 comments:

  1. WHAT AN AMAZING SUMMARY OF THE WHOLE ORACLE FORM !!!! AND THANX

    ReplyDelete
  2. It is developed magnificently in an interview point of view...Thanks man...Keep giving such articles and tell me if u need any help. I am also working as oracle developer

    ReplyDelete
  3. This is simply awesome. Great effort. Exactly what I was looking for. Looking forward for more posts on Oracle forms 10g.

    ReplyDelete
  4. Excellent work.

    I just had to go through this article to re-visit the technical stuff before the interview.

    Thanks.

    ReplyDelete
    Replies
    1. This is simply great. The whole Info. on forms & reports which can be used at the time of interview.

      Delete
  5. Hi,
    My requirement is when we click on book order button on sales order form then my custom package will validate all the values items, quantities on the order. If validation fails then it should display custom message or popup and need to prevent booking.

    ReplyDelete