How to evaluate the dynamic condition string in PL/SQL ?

Question

Hello, I am solving the issue of checking and validating the event table.
For Example, the event table namely "Contract_validated" contains some atts about a contract as follow:
CONTRACT_VALIDATED (SEQ_ID, CO_ID, VALID_T, CHANGE_KEY, ATT1, ATT1_FROM, ATT2, ATT2_FROM, REASON, CHANGE_KEY_ORIG, ATT1_ORIG, ATT2_ORIG)
In this table, the pairs (ATT1 and ATT1_FROM), (ATT2 and ATT2_FROM) must be compared to check whether the values are changed or not in the update event (change_key = U). If some records have change_key = U but the values does not change, I need to protocol and correct such records.
The table name and attributes list could be dynamic, and will be provided as parameters. Therefore, I use Dynamic PL/SQL to generate the code to test the conditions between the values between the pairs columns for detecting the invalid event. However, I am stucking in testing the condition phrases because I can not evaluate the condition string in the SELECT statement. I can not use IF because parts of this condition string take the value from a record and collection type. Anyone has the idea how to evaluate the condition in such case, please give me instructions or recommendations (it could be other alternatives to solve the problems)
Here is the code which generated from my Dynamic PL/SQL string, however, Oracle raise exception error at the EXECUTE IMMEDIATE v_sql command
SELECT 'x' FROM DUAL WHERE (NVL(v_rec.ATT1, NULL) <> NVL(v_rec.ATT1_FROM , NULL) OR (NVL(v_rec.ATT2, NULL) <> NVL(v_rec.ATT2_FROM , NULL))
E-0008: Unkown Exception raised in Loop. ORACLE:ORA-00904: "V_REC"."ATT2_FROM": invalid identifier
vo_traced_list has type Table of VARCHAR2(2000), storing the atts list of table (CONTRACT_VALIDATED), it has value already from other procedure invocation.
Here is the dynmic PL/SQL code generated dynamically depends on the table name, and attr list:
DECLARE v_rec CONTRACT_VALIDATED%ROWTYPE;
TYPE cv_type IS REF CURSOR;
v_rec_cv CV_TYPE;
v_cond VARCHAR2(4000);
cond BOOLEAN := FALSE;
v_exec VARCHAR2(1000);
v_default VARCHAR2(10):= 'NULL';
tk_val CONTRACT_VALIDATED.VALID_T%TYPE;
pk_val CONTRACT_VALIDATED.CO_ID%TYPE;
v_cnt NUMBER;
BEGIN
OPEN v_rec_cv FOR SELECT /*+ parallel(x,4) */ x.* FROM CONTRACT_VALIDATED x WHERE CHANGE_KEY = 'U' ORDER BY VALID_T;
FETCH v_rec_cv INTO v_rec;
IF v_rec_cv%NOTFOUND THEN
Add_Log('Event_Validating',v_user,v_event_validated,'INFO','I-0001: No-Procession needed');
ELSE
BEGIN
LOOP
pk_val := v_rec.co_id;
tk_val := v_rec.valid_t;
v_cnt := vo_traced_atts_list.COUNT;
v_cond := '(NVL(v_rec.'|| vo_traced_atts_list(1)||', ' || v_default || ') <> NVL(v_rec.' || vo_traced_atts_list(1)||'_FROM'
||' , ' || v_default || '))';
cond := (BOOLEAN) v_cond;
FOR v_i IN 2..v_cnt LOOP
BEGIN
v_cond := v_cond ||CHR(13)||CHR(10)||'OR (NVL(v_rec.'||vo_traced_atts_list(v_i)||', ' || v_default || ') <> NVL(v_rec.'||vo_traced_atts_list(v_i)||'_FROM'
||' , ' || v_default || '))';
END;
END LOOP;
v_exec := 'SELECT ''x'' FROM DUAL WHERE '||v_cond;
Add_Log('Event_Validating',v_user,v_event_validated,'INFO',v_exec);
EXECUTE IMMEDIATE v_exec;
/* Exception raised from here
E-0008: Unkown Exception raised in Loop. ORACLE:ORA-00904: "V_REC"."ATT2_FROM": invalid identifier
It seems that Oracle does not understand the dynamic reference v_rec.ATT2_FROM, v_rec.ATT2,... to test the condtion
IF SQL%ROWCOUNT = 0     THEN -- condition is false ==> traced attributes does not changed
-- update the REASON = 4 - not interested event
v_exec := 'UPDATE CONTRACT_VALIDATED SET REASON = 4 WHERE CO_ID = '||pk_val||' AND VALID_T = '||tk_val;
EXECUTE IMMEDIATE v_exec;
END IF;
FETCH v_rec_cv INTO v_rec;
EXIT WHEN v_rec_cv%NOTFOUND;
END LOOP;
EXCEPTION
WHEN OTHERS THEN
Add_Log('SCD_VALIDATION',v_user,v_event_validated,'ERROR','E-0008: Unkown Exception raised in Loop. ORACLE:'||SQLERRM);
RAISE ge_raise_error;
END;
END IF;
CLOSE v_rec_cv;
EXCEPTION
WHEN OTHERS THEN
Add_Log('SCD_VALIDATION',v_user,v_event_validated,'ERROR','E-0008: Unkown Exception raised in Loop. ORACLE:'||SQLERRM);
RAISE ge_raise_error;
END;

Answer 1

Dear Andrew,
Thank you so much for your suggestions, however, I think it will be better to let me explain more about the situation.
I am working at Data Warehousing and Analysis part. The event tables are provided by other applications such as Customer OTLP system, Sales Management, etc. We therefore just have the results stored in the event tables (which could be wrong or inconsistency) and no way to force them to be valid by constraints. Before further processing the events , their records should be checked and overridden if possible, and that is the point I am trying to solve now.
The Event table names, their attributes list, data types, primary key, timestamp columns etc are dynamic and are provided via parameters. I would like to write a procedure which can check the invalid events (not only update, but also insert, delete), protocol them, and override them if possible before processing further. Because the table name, attribute lists, data type, etc are not known in advanced, to my best knowledge, the only choice is generating dynamic PL/SQL code although it could suck the performance. The code you have seen in my first question is the output from the follwoing procedure, where the i_att_list provides the atts list has been parsed from other procedure invocation, i_pk is the primary key, i_tk is the time key, i_table_name is the table name (which is Event_Validation in previous example). The stucking point I have met now is that I do not know how to test the condition to detect the different between column pairs (ATT1 and ATT1_FROM, ...). Using Select from dual is just a dummy select for testing the where condition which must be formed as a string by that way.
Thank you very much for your answer and looking forward to seeing your further recommendations or suggestions.
Regards,
Tho.
CREATE OR REPLACE PROCEDURE Update_Validation
( i_att_list enum_string, -- list of attributes
i_pk IN VARCHAR2, -- primary key column
i_tk IN VARCHAR2, -- time key column
i_table_name IN VARCHAR2 -- table_name - the columns format be checked
) AUTHID Current_User IS
TYPE LoopCurType           IS REF CURSOR;
ln_parallel NUMBER := 4;
ge_raise_error EXCEPTION;
v_user VARCHAR2(100);
v_sql VARCHAR2(4000);
v_string VARCHAR2(4000);
v_crlf VARCHAR2(2) := CHR(13)||CHR(10);
BEGIN
SELECT sys_context('USERENV','current_schema') INTO v_user FROM DUAL;
v_sql:= 'SELECT /*+ parallel(x,'||ln_parallel||') */ x.* FROM ' ||i_table_name|| ' x '||
          'WHERE CHANGE_KEY = ''U'''||
' order by '||i_tk;
v_string := 'DECLARE v_rec '||i_table_name||'%ROWTYPE;' ||v_crlf||
          ' TYPE cv_type IS REF CURSOR; ' ||v_crlf||
' v_rec_cv CV_TYPE; ' ||v_crlf||
          ' v_cond VARCHAR2(4000); ' ||v_crlf||
     ' v_exec VARCHAR2(100);' ||v_crlf||
          ' v_default VARCHAR2(10):= ''~~''; ' ||v_crlf||
' tk_val '||i_table_name||'.'||i_tk||'.%TYPE;'||v_crlf||
' pk_val '||i_table_name||'.'||i_pk||'.%TYPE;'||v_crlf||
          ' v_cnt NUMBER;' ||v_crlf||
          'BEGIN ' ||v_crlf||
                    'OPEN v_rec_cv FOR ' ||v_sql ||';' ||v_crlf||
                    'FETCH v_rec_cv INTO v_rec;' ||v_crlf||
                         ' IF v_rec_cv%NOTFOUND THEN ' ||v_crlf||
                              'Add_Log(''Event_Validating'',v_user,i_table_name,''INFO'',''I-0001: No-Procession needed'');'||v_crlf||
                         ' ELSE ' ||v_crlf||
                              ' BEGIN '||v_crlf||
                              ' LOOP '||v_crlf||
                              'pk_val := v_rec.'||i_pk||';'||v_crlf||
'tk_val := v_rec.'||i_tk||';'||v_crlf||
'v_cnt := i_att_list.COUNT;' ||v_crlf||
                                        'v_cond := ''NVL(v_rec.''|| i_att_list(1)||'', '' || v_default || '') <> NVL(v_rec.'' || i_att_list(1)||''_FROM'''||v_crlf||
                         '||'' , '' || v_default || '')'';'||v_crlf||
                                        'FOR v_i IN 2..v_cnt LOOP'||v_crlf||
                                             'BEGIN'||v_crlf||
                                             'v_cond := v_cond ||CHR(13)||CHR(10)||''OR NVL(v_rec.''||i_att_list(v_i)||''), <> NVL(v_rec.''||i_att_list(v_i)||''_FROM'''||v_crlf||
                                             '||'' , '' || v_default || '')'';'||v_crlf||
                                             'END;'||v_crlf||
                                        'END LOOP;'||v_crlf||
                                        'v_exec := ''SELECT ''x'' FROM DUAL WHERE ''||v_cond;'||v_crlf||
                                        'EXECUTE IMMEDIATE v_exec;'||v_crlf||
                                        'IF SQL%ROWCOUNT = 0     THEN -- condition is false ==> traced attributes does not changed'||v_crlf||
                                        '-- update the REASON = 4 - not interested event'||v_crlf||
                                        'UPDATE '||i_table_name||' SET REASON = 4 WHERE '||i_pk||' = '||v_tk||' AND '||i_tk||' = '||tk_val||';'||v_crlf||
                                        'END IF;'||v_crlf||
                                   'FETCH v_rec_cv INTO v_rec;' ||v_crlf||
                                   'EXIT WHEN v_rec_cv%NOTFOUND;'||v_crlf||
                    ' END LOOP;'||v_crlf||
                              'EXCEPTION' ||v_crlf||
                         'WHEN OTHERS THEN'||v_crlf||
                    'Add_Log(''SCD_VALIDATION'',v_user,i_table_name,''ERROR'',''E-0008: Unkown Exception raised in Loop. ORACLE:''||SQLERRM);'||v_crlf||
                    'RAISE ge_raise_error;'||v_crlf||
                              'END;'||v_crlf||
                              'END IF;'|| v_crlf||
                    'Close v_rec_cv;'||v_crlf||
                    'EXCEPTION' ||v_crlf||
               'WHEN OTHERS THEN'||v_crlf||
          'Add_Log(''SCD_VALIDATION'',v_user,i_table_name,''ERROR'',''E-0008: Unkown Exception raised in Loop. ORACLE:''||SQLERRM);'||v_crlf||
          'RAISE ge_raise_error;'||v_crlf||
               'END;';               
     Add_Log('SCD_UPDATE_VALIDATION',v_user,i_table_name,'INFO','I-0006: Update Validation : '||v_string);     
     EXECUTE IMMEDIATE v_string;
EXCEPTION
WHEN OTHERS THEN
Add_Log('SCD_VALIDATION',v_user,i_table_name,'ERROR','E-0008: Unkown Exception raised in Loop. ORACLE:'||SQLERRM);
END Update_Validation;