Available Events/Attributes in Triggers

1) Available Events/Attributes in Triggers
1@@@@ All the DDL events
Table 19-1 lists the DDL events for which triggers can be coded. Each event can have
a BEFORE and an AFTER trigger.

Table 19-1. Available DDL events
DDL event             Fires when...
ALTER                 Any database object is altered using the SQL ALTER command
ANALYZE               Any database object is analyzed using the SQL ANALYZE command
ASSOCIATE
STATISTICS            Statistics are associated with a database object
AUDIT                 Auditing is turned on using the SQL AUDIT command
COMMENT               Comments are applied to a database object
CREATE                Any database object is created using the SQL CREATE command
DDL                   Any of the events listed here occur
DISASSOCIATE
STATISTICS            Statistics are disassociated from a database object
DROP                  Any database object is dropped using the SQL DROP comm
GRANT                 Privileges are granted using the SQL GRANT command
NOAUDIT               Auditing is turned off using the SQL NOAUDIT command
RENAME                A database object is renamed using the SQL RENAME command
REVOKE                Privileges are revoked using the SQL REVOKE command
TRUNCATE              A table is truncated using the SQL TRUNCATE command

As with DML triggers, these DDL triggers fire when the event to which they are attached
occurs within the specified database or schema. There is no limit to the number of
trigger types that can exist in the database or schema.



2@@@@Available Attributes
Oracle provides a set of functions (defined in the DBMS_STANDARD package) that
provide information about what fired the DDL trigger and other information about the
trigger state (e.g., the name of the table being dropped). Table 19-2 displays these trigger
attribute functions. The following sections offer some examples of usage.

Like userenv() function return information about client.

Table 19-2. DDL trigger event and attribute functions
Name                        Returns...
ORA_CLIENT_IP_ADDRESS       IP address of the client.
ORA_DATABASE_NAME           Name of the database.
ORA_DES_ENCRYPTED_
PASSWORD                    DES-encrypted password of the current user.
ORA_DICT_OBJ_NAME           Name of the database object affected by the firing DDL.
ORA_DICT_OBJ_NAME_LIST      Count of objects affected. It also returns a complete list
                            of objects affected in the NAME_LIST parameter,
                            which is a collection of type DBMS_STANDARD.ORA_NAME_LIST_T.
ORA_DICT_OBJ_OWNER          Owner of the database object affected by the firing DDL.
ORA_DICT_OBJ_OWNER_LIST     Count of objects affected. It also returns a complete list
                            of object owners affected in the NAME_LIST parameter, which is
                            a collection of type DBMS_STANDARD.ORA_NAME_LIST_T.
ORA_DICT_OBJ_TYPE           Type of database object affected by the firing DDL
                            (e.g., TABLE or INDEX).
ORA_GRANTEE                 Count of grantees. The USER_LIST argument contains the full
                            list of grantees, which is a collection of
                            type DBMS_STANDARD.ORA_NAME_LIST_T.
ORA_INSTANCE_NUM            Number of the database instance.
ORA_IS_ALTER_COLUMN         TRUE if the specified COLUMN_NAME argument is being altered,
                            or FALSE if not.
ORA_IS_CREATING_NESTED_
TABLE                       TRUE if a nested table is being created, or FALSE if not.
ORA_IS_DROP_COLUMN          TRUE if the specified COLUMN_NAME argument is indeed being
                            dropped, or FALSE if not.
ORA_LOGIN_USER              Name of the Oracle user for which the trigger fired.
ORA_PARTITION_POS           Position in the SQL command where a partitioning clause
                            could be correctly added.
ORA_PRIVILEGE_LIST          Number of privileges being granted or revoked. The PRIVILEGE_LIST
                            argument contains the full list of privileges affected,
                            which is a collection of type DBMS_STANDARD.ORA_NAME_LIST_T.
ORA_REVOKEE                 Count of revokees. The USER_LIST argument contains the full
                            list of revokees, which is a collection of
                            type DBMS_STANDARD.ORA_NAME_LIST_T.
ORA_SQL_TXT                 Number of lines in the SQL statement firing the trigger.
                            The SQL_TXT argument returns each line of the statement,
                            which is an argument of type DBMS_STANDARD.ORA_NAME_LIST_T.
ORA_SYSEVENT                Type of event that caused the DDL trigger to fire
                            (e.g., CREATE, DROP, or ALTER).
ORA_WITH_GRANT_OPTION       TRUE if privileges were granted with the GRANT option,
                            or FALSE if not.


Note the following about the event and attribute functions:
 ~ The datatype ORA_NAME_LIST_T is defined in the DBMS_STANDARD package
   as:
     TYPE ora_name_list_t IS TABLE OF VARCHAR2(64);
   In other words, this is a nested table of strings, each of which can contain up to 64
   characters.

 ~ The DDL trigger event and attribute functions are also defined in the
   DBMS_STANDARD package. Oracle creates a standalone function (which adds
   the ¡°ORA_¡± prefix to the function name) for each of the packaged functions by
   executing the $ORACLE_HOME/rdbms/dbmstrig.sql script during database creation.
   In some releases of the Oracle database, there are errors in this script that
   cause the standalone functions to not be visible or executable. If you feel that these
   elements have not been properly defined, you should ask your DBA to check the
   script for problems and make the necessary corrections.

 ~ The USER_SOURCE data dictionary view does not get updated until after both
   BEFORE and AFTER DDL triggers are fired. In other words, you cannot use these
   functions to provide a ¡°before and after¡± version control system built entirely
   within the database and based on database triggers.



3@@@@ Working with Events and Attributes
  Here is a trigger that prevents any and all database objects from being created:
    TRIGGER no_create
    AFTER CREATE ON SCHEMA
    BEGIN
      RAISE_APPLICATION_ERROR (
        -20000,
      'ERROR : Objects cannot be created in the production database.'
      );
    END;
  After installing this trigger, attempts at creating anything meet with failure:
    SQL> CREATE TABLE demo (col1 NUMBER);
    *
    ERROR at line 1:
    ORA-20000: Objects cannot be created in the production database.

  That is a rather terse and uninformative error message. There was a failure, but what
  failed? Wouldn¡¯t it be nice to have a little more information in the error message, such
  as the object I was attempting to create?
    /* File on web: no_create.sql */
    TRIGGER no_create
    AFTER CREATE ON SCHEMA
    BEGIN
      RAISE_APPLICATION_ERROR (-20000,
        'Cannot create the ' || ORA_DICT_OBJ_TYPE  ||
        ' named '            || ORA_DICT_OBJ_NAME  ||
        ' as requested by '  || ORA_DICT_OBJ_OWNER ||
        ' in production.');
    END;
  With this trigger installed, an attempt to create my table now offers much more diagnostic
  information:
    SQL> CREATE TABLE demo (col1 NUMBER);
    *
    ERROR at line 1:
    ORA-20000: Cannot create the TABLE named DEMO as requested by SCOTT in production


  I could even place this logic within a BEFORE DDL trigger and take advantage of the
  ORA_SYSEVENT attribute to respond to specific events:
    @@@Example:
    HR@ocm> !cat tmp.sql
    CREATE OR REPLACE TRIGGER no_create
      BEFORE DDL ON SCHEMA
    BEGIN
       IF ORA_SYSEVENT = 'CREATE'
       THEN
          RAISE_APPLICATION_ERROR (  -20000,
        'Cannot create the '|| ORA_DICT_OBJ_TYPE  ||
        ' named '           || ORA_DICT_OBJ_NAME  ||
        ' as requested by ' || ORA_DICT_OBJ_OWNER );
       ELSIF ORA_SYSEVENT = 'DROP'
       THEN
          DBMS_OUTPUT.put_line('You droped the table '
        || ORA_DICT_OBJ_NAME || '. I knew it.');
       END IF;
    END;
    /
   
    HR@ocm> @tmp.sql
    HR@ocm> CREATE TABLE test_ora_sysevent(a number);
    CREATE TABLE test_ora_sysevent(a number)
    *
    ERROR at line 1:
    ORA-00604: error occurred at recursive SQL level 1
    ORA-20000: Cannot create the TABLE named TEST_ORA_SYSEVENT as requested by HR
    ORA-06512: at line 4
   
    HR@ocm> DROP TRIGGER audit_test;
    You droped the table AUDIT_TEST. I knew it.


I can use the ORA_IS_ALTER_COLUMN function to decipher which column was
altered by an ALTER TABLE statement. Here is one example:

@@@Example: you could control the logic using ORA_DICT_OBJ_XXX.
            here I apply it to ALTER TABLE DDL language.
    HR@ocm> !cat tmp.sql
    CREATE OR REPLACE TRIGGER preserve_app_cols
      AFTER ALTER ON SCHEMA
    DECLARE
       CURSOR curs_get_col
            (  owner_in  IN  VARCHAR2
             , tname_in  IN  VARCHAR2 )
       IS
          SELECT column_name
            FROM all_tab_columns
           WHERE owner= owner_in AND  table_name = tname_in;
       
       --private function to judge whether it is key table column
       --cannot alter defination of hr.employees.salary
        FUNCTION is_application_column
            (  owner_in  IN  VARCHAR2
             , tname     IN  VARCHAR2
             , col_name  IN  VARCHAR2 )
          RETURN BOOLEAN
        IS
        BEGIN
           IF owner_in = 'HR' THEN
              IF tname = 'EMPLOYEES' THEN
                 IF col_name = 'SALARY' THEN
                        RETURN TRUE;
                     ELSE
                    RETURN FALSE;
                 END IF;
              END IF;
           END IF;          
        END is_application_column;
   
    BEGIN
       IF ORA_DICT_OBJ_TYPE = 'TABLE' THEN
          FOR rec IN curs_get_col(  ORA_DICT_OBJ_OWNER
                                  , ORA_DICT_OBJ_NAME  )
          LOOP
             IF ora_is_alter_column ( rec.column_name ) THEN
                IF is_application_column (  ORA_DICT_OBJ_OWNER
                                          , ORA_DICT_OBJ_NAME
                                          , rec.column_name   ) THEN
                   RAISE_APPLICATION_ERROR( -20000,
                       'Cannot alter core application attributes' );
                 END IF;  -- table/column is core
              END IF;  -- current column was altered
           END LOOP; -- every column in the table
       END IF; -- table was altered
    END;
    /
    HR@ocm> alter table employees modify (salary NUMBER(10,2));
    alter table employees modify (salary NUMBER(10,2))
    *
    ERROR at line 1:
    ORA-00604: error occurred at recursive SQL level 1
    ORA-20000: Cannot alter core application attributes
    ORA-06512: at line 39


3@@@@ Trigger DDL

   @@@Create DDL trigger for displaying the DDL statement describe information
    HR@ocm> !cat tmpx.sql
    CREATE OR REPLACE TRIGGER town_crier
    AFTER CREATE ON SCHEMA
    BEGIN
       DBMS_OUTPUT.put_line
        (  'I believe you have created a '
        || ORA_DICT_OBJ_TYPE || ' called '
        || ORA_DICT_OBJ_NAME  );
    END;
    /
    HR@ocm> @tmpx.sql
    Trigger created.
   
   @@@Now, the information about DDL statement would be traced and display
    HR@ocm> !cat tmp.sql
    SET SERVEROUTPUT ON
    SET FEEDBACK OFF
    DROP TABLE a_table
    /
    CREATE TABLE a_table (col1 NUMBER)
    /
    CREATE INDEX an_index ON a_table(col1)
    /
    DROP FUNCTION a_function
    /
    CREATE FUNCTION a_function RETURN BOOLEAN AS
    BEGIN
      RETURN(TRUE);
    END;
    /
    /*-- a CRLF to flash DBMS_OUTPUTs buffer */
    EXEC DBMS_OUTPUT.put_line(chr(10));
   
    HR@ocm> @tmp.sql
    I believe you have created a TABLE called A_TABLE
    I believe you have created a INDEX called AN_INDEX
    I believe you have created a FUNCTION called A_FUNCTION




referencing "Oracle PL/SQL Program Design 5th Edition"