Oracle Forms : Query Triggers

1. Query Triggers

2. Objectives
• How Query Processing occurs in Forms?
• Writing Pre-Query Trigger
• Writing Post-Query Trigger
• Scope of the triggers and Built-ins

3. Query Processing
Perform queryPerform query
Fetch a row into a new recordFetch a row into a new record
Mark record as validMark record as valid
Fire Post-Query triggerFire Post-Query trigger
Validate any record changesValidate any record changes
Abort query
on failure
Flush
record
on failure
Construct SELECT...Construct SELECT...
Fire Pre-Query triggerFire Pre-Query trigger

4. Where & Order By Clauses
• Three sources for Where Clause
– Query/Where Dialog Box
– Example Record
– Where Clause Block Property
Where Clauses are combined by the AND Operator.
• Two sources for Order By Clause
– Order by Clause Block Property
– Query/Where Dialog Box
Second source for Order by clause Overrides the first one.

5. SELECT statement Issued
SELECT base_column, ..., ROWID
INTO :base_item, ..., :ROWID
FROM base_table
WHERE default_where_clause
AND (example_record_conditions)
AND (query_where_conditions)
ORDER BY default_order_by_clause |
query_where_order_by

6. Pre-Query Trigger
• Defined at the Block-level
• Fires once before the query is issued.
IF :emp.enmpno||:emp.ename|| :emp.hiredate IS NULL THEN
MESSAGE(‘You must query on emp id or name or joindate’);
RAISE form_trigger_failure; --Built-in Exception
END IF;

7. Post-Query Trigger
• Written at Block level
• Use to populate nondatabase items and calculate statistics
• Fires once for each fetched record.
• SELECT dname INTO :control.dept_name
FROM dept
WHERE deptno=:emp.deptno;

8. Query Array Processing
• Reduces network traffic
• Enables Query Array processing:
– Enable Array Processing option
– Set Query Array Size property
• Query Array Size property
• Query All Records property

9. Enter-Query Mode
• Some triggers may fire in Enter-Query mode.
• Set to fire in Enter-Query Mode property.
• Test mode during execution with :SYSTEM.MODE
– NORMAL
– ENTER-QUERY
– QUERY
IF :SYSTEM.MODE = ’NORMAL’ THEN
ENTER_QUERY;
ELSE
EXECUTE_QUERY;
END IF;

10. Query Info at Runtime
• SYSTEM.MODE
• SYSTEM.LAST_QUERY
–Contains bind variables (EMPNO = :1) before
SELECT_RECORDS
–Contains actual values (EMPNO = 7566) after
SELECT_RECORDS

11. Query Info at Runtime
• GET_BLOCK_PROPERTY SET_BLOCK_PROPERTY
– Get and set:
DEFAULT_WHERE
ORDER_BY
QUERY_ALLOWED
QUERY_HITS
– Get only:
QUERY_OPTIONS
RECORDS_TO_FETCH

12. Query Info at Runtime
• GET_ITEM_PROPERTY
SET_ITEM_PROPERTY
– Get and set:
CASE_INSENSITIVE_QUERY
QUERYABLE
QUERY_ONLY
– Get only:
QUERY_LENGTH

13. Summary
• Where clauses are combined with AND Operator
• Second Order by Overrides the first one.
• A Pre-Query trigger fires before a query executes. Use it to check or
modify query conditions.
• A Post-Query trigger fires as each record is fetched. Use it to perform
calculations and populate additional items.