Apex beginner here. I have a view in my Oracle database of the form:
create or replace view vw_awkward_view as
select unique tab1.some_column1,
tab2.some_column1,
tab2.some_column2,
tab2.some_column3
from table_1 tab1,
table_2 tab2
WHERE ....
I need the 'unique' clause on 'tab1.some_column1' because it has many entries in its underlying table. I also need to include 'tab1.some_column1' in my view because the rest of the data doesn't make much sense without it.
In Apex, I want to create a report on this view with a form for editing it (update only). I do NOT need to edit tab1.some_column1. Only the other columns in the view need to be editable. I can normally achieve this using an 'instead-of' trigger, but this doesn't look possible when the view contains a 'distinct', 'unique' or 'group by' clause.
If I try to update a row on this view I get the following error:
ORA-02014: cannot select FOR UPDATE from view with DISTINCT, GROUP BY, etc.
How can I avoid this error? I want my 'instead-of' trigger to kick in and perform the update and I don't need to edit the column which has the 'unique' clause, so I think it should be possible to do this.
I think that you should be able to remove the "unique".
if tab2.some_column1, tab2.some_column2, tab2.some_column3 are not unique, then how do you want to update them ?
if they are unique then the whole result: tab1.some_column1, tab2.some_column1, tab2.some_column2, tab2.some_column3 is unique.
When you state in a sql query "unique" or "distinct" it's for all columns not only 'tab1.some_column1'
Hope i'm in the correct direction of your question here ;)
Your query could be achieved by doing something like:
select a.some_column1, tab2.some_column1, tab2.some_column2, tab2.some_column3
from table_2 tab2
join (select distinct some_column1 from table_1) a
on tab2.column_in_tab1 = a.some_column1
The reason you get the ORA-02014 error is because of the automatically generated ApplyMRU process. This process will attempt to lock a (the) changed row(s):
begin
for r in (select ...
from vw_awkward_view
where <your first defined PK column>= 'value for PK1'
for update nowait)
loop
null;
end loop;
end;
That's a bummer, and means you won't be able to use the generated process. You'll have to write your own process which does the updating.
For this, you'll have to use the F## arrays in apex_application.
If this sounds totally unfamiliar, take a look at:
Custom submit process, and on using the apex_application arrays.
Also, here is a how-to for apex from 2004 from Oracle itself. It still uses lots of htmldb references, but the gist of it is there.
(it might be a good idea to use the apex_item interface to build up your form, and have control over what is generated and what array it takes.)
What it comes down to is: loop over the array containing your items and do an UPDATE on your view with the submitted values.
Of course, you don't have locking this way, nor a way to prevent unnecessary updates.
Locking you can do yourself, with for example using the select for update method. You'd have to lock the correct rows in the table(s) you want to alter, before you update them. If the locking fails, then your process should fail.
As for the 'lost update' story: here you'd need to check the MD5-checksums. A checksum is generated from the editable columns in your form and put in the html-code. On submit, this checksum is then compared to a newly generated checksum from those same columns, but with values from the database at that time of submit. If the checksums differ, it means the record has changed between the page load and the page submit. Your process should fail because the record has been altered, and you don't want to have those overwritten. (if you go the apex_item way, then don't forget to include an MD5_CHECKSUM call (or MD5_HIDDEN).
Important note though: checksums generated by either using apex_item or simply the standard form functionality build up a string to be hashed. As you can see in apex_item.md5_hidden, checksums are generated using DBMS_OBFUSCATION_TOOLKIT.MD5.
You can get the checksum of the values in the DB in 2 ways: wwv_flow_item.md5 or using dbms_obfuscation.
However, what the documentation fails to mention is this: OTN Apex discussion on MD5 checksums. Pipes are added in the generated checksums! Don't forget this, or it'll blow up in your face and you'll be left wondering for days what the hell is wrong with it.
Example:
select utl_raw.cast_to_raw(dbms_obfuscation_toolkit.md5(input_string=>
"COLUMN1" ||'|'||
"COLUMN2" ||'|'||
"COLUMN5" ||'|'||
"COLUMN7" ||'|'||
"COLUMN10" ||'|'||
"COLUMN12" ||'|'||
"COLUMN14" ||
'|||||||||||||||||||||||||||||||||||||||||||'
)) md5
from some_table
To get the checksum of a row of the some_table table, where columns 1,2,5,7,10,12,14 are editable!
In the end, this is how it should be structured:
loop over array
generate a checksum for the current value of the editable columns
from the database
compare this checksum with the submitted checksum
(apex_application.g_fcs if generated) if the checksums match,
proceed with update. If not, fail process here.
lock the correct records for updating. Specify nowait, and it
locking fails, fail the process
update your view with the submitted values. Your instead-of trigger
will fire. Be sure you use correct values for your update statement so that only this one record will be updated
Don't commit inbetween. It's either all or nothing.
I almost feel like i went overboard, and it might feel like it is all a bit much, but when you know the pitfalls it's actually not so hard to pull this custom process off! It was very knowledgable for me to play with it :p
The answer by Tom is a correct way of dealing with ths issue but I think overkill for your requirements if I understand correctly.
The easiest way may be to create a form on the table you want to edit. Then have the report edit link take the user to this form which will only update the needed columns from the one table. If you need the value of the column from the other table displayed it is simple when you create the link to pass this value to the form which can contain a display only item to show this.
Related
I am developing an order transaction where a user can order a product. Once they clicked the 'add to cart' button, it will be able to save on the database in how many times they want with the same order id. Order id is like a transaction id.
My problem is that whenever I want to display the items that customer ordered, it displays an error or ORA 01422. How can I resolve this error?
Here is my code
DECLARE
order_item_id NUMBER;
BEGIN
order_item_id := :MOTOR_PRODUCTS_ORDER.M_ORDERID;
SELECT MOTOR_ID,
MOTOR_QTY_PURCHASED,
UNITPRICE
INTO :MOTOR_ORDER_ITEMS.MOTOR_ID,
:MOTOR_ORDER_ITEMS.MOTOR_QTY_PURCHASED,
:MOTOR_ORDER_ITEMS.UNITPRICE
FROM MOTOR_ORDERS
WHERE motor_order_id = order_item_id;
END;
As krokodilo says, this error is caused because your query returns multiple rows. Depending on what you want to do, you have a couple of options.
If you want multiple values then either use a loop and process them one row at a time (if you are going to be performing a dml operation use bulk collect). If you only want a single row then narrow your result set down with an extra where clause, or use MAX to ensure you only get one value back.
If there is more than one row which will be returned from a query you'll need to use a cursor. One way to do this is with a cursor FOR loop:
DECLARE
order_item_id NUMBER;
BEGIN
order_item_id := :MOTOR_PRODUCTS_ORDER.M_ORDERID;
FOR aRow IN (SELECT MOTOR_ID, MOTOR_QTY_PURCHASED, UNITPRICE
FROM MOTOR_ORDERS
WHERE motor_order_id = order_item_id)
LOOP
-- Do something here with the values in 'aRow'. For example, you
-- might print them out:
DBMS_OUTPUT.PUT_LINE('MOTOR_ID=' || aRow.MOTOR_ID ||
' MOTOR_QTY_PURCHASED=' || aRow.MOTOR_QTY_PURCHASED ||
' UNITPRICE=' || aRow.UNITPRICE);
END LOOP;
END;
Best of luck.
This looks like a Forms question; is it? If so, my suggestion is to let Forms do that job for you.
According to what you posted, there are two blocks:
MOTOR_PRODUCTS_ORDER (a master block, form type)
MOTOR_ORDER_ITEMS (a detail block, tabular type)
I guess that there is a master-detail relationship between them. If there's none, I'd suggest you to create it. Although you can make it work without such a relationship, it'll be much more difficult. If you are unsure of how to do it, start from scratch:
delete MOTOR_ORDER_ITEMS block (detail)
create it once again, this time by following the Data Block Wizard
Set MOTOR_PRODUCTS_ORDER to be its master block
Relationship is on ORDER_ID column/item
Let's presume that by this point everything is set up. Retrieving items that belong to that ORDER_ID is now very simple:
navigate to master block
enter query mode
enter value into an item that represents ORDER_ID
execute query
End of story. Forms triggers & procedures (which were created by the Wizard) will do its job and retrieve both master and detail records.
No need for additional coding; if you're skilled developer, you can create such a form in a matter of minutes. Won't be beautiful, but will be effective & reliable.
There's really no use in doing it manually, although it is possible. Your code works if there's a single item for that ORDER_ID. For two or more items, as you already know, it'll fail with TOO-MANY-ROWS error.
Basically, if you insist, you should use a loop:
you'd enter ORDER_ID into the master block
as you need to move through the detail block, i.e. use NEXT_RECORD, which is a restricted procedure, you can't use number of triggers (open Forms Online Help System and read about them) so a "Show items" button (with its WHEN-BUTTON-PRESSED trigger) might be just fine
a cursor FOR loop would be your choice
for every row it fetches, you'd populate block items and
navigate to next record (otherwise, you'd keep overwriting existing values in the 1st tabular block row)
As I said: possible, but not recommended.
I have a table of people who belong to various sites. These sites can change, but don't very often. So when we create an attendance record (a learner_session object) we don't store the site. But this has cause a problem in reporting how many training hours a site has, because some people have changed sites over the years. Not by much, but we'd like to get this right.
So I've added a site_at_the_time column to the learner_session table. I want to auto-populate this with the site the person was at when they attended the session. But I'm not sure how to reference this. For some reason (I'm guessing to speed development or something) the learner_id is allowed to be null. So I'm currently planning to do an update trigger. The learner_id shouldn't ever get updated, and if it ever did somehow, the entire record would be junk so I'm not worried about it overwriting it.
The trigger I have now is
create trigger set_site_at_the_time
after update of learner_id on lrn_session
begin
:new.site_at_the_time:= (select site_id from learner who where :new.learner_id = who.learner_id);
end;
which leads me to the following error:
ORA-04082: NEW or OLD references not allowed in table level triggers
Now, I've done some research and found I need to use a FOR EACH ROW - and I'm wondering what exactly this FOR EACH ROW does - is it every row captured by the trigger? Or is it every row in the table?
Also, will this trigger when I create a record too? So if I do insert into learner_session(id,learner_id,...) values(learner_session_id_seq.nextval,1234,...) will this capture that appropriately?
And while I'm here, I might as well see if there's something else I'm doing wrong with this trigger. But I'm mainly asking to figure out what the FOR EACH ROW is supposed to do and if it triggers properly. =)
FOR EACH ROW means that the trigger will fire once for each row that is updated by your SQL statement. Without this clause, the trigger will only fire once, no matter how many rows are affected. If you want to change values as they're being inserted, you have to use FOR EACH ROW, because otherwise the trigger can't know which :new and :old values to use.
As written, the trigger only fires on update. To make it also fire upon insert, you'd need to change the definition:
CREATE TRIGGER set_site_at_the_time
BEFORE INSERT OR UPDATE OF learner_id
ON lrn_session
FOR EACH ROW
BEGIN
SELECT site_id into :new.site_at_the_time
FROM learner who
WHERE :new.learner_id = who.learner_id);
END set_site_at_the_time;
Long time user, first time "asker".
I am attempt to construct an Oracle procedure and/or trigger that will compare two tables with the MINUS operation and then insert any resulting rows into another table. I understand how to do the query in standard SQL, but I am having trouble coming up with an efficient way to do this using PL/SQL.
Admittedly, I am very new to Oracle and pretty green with SQL in general. This may be a silly way to go about accomplishing my goal, so allow me to explain what I am attempting to do.
I need to create some sort of alert that will be triggered when the V_$PARAMETER view is changed. Apparently triggers can not respond to changes to view but, instead, can only replace actions on views...which I do not wish to do. So, what I did was create a table that to mirror that view to essentially save it as a "snapshot".
create table mirror_v_$parameter as select * from v_$parameter;
Then, I attempted to make a procedure that would minus these two so that, whenever a change is made to v_$parameter, it will return the difference between the snapshot, mirror_v_$parameter. I trying to create a cursor with the command:
select * from v_$parameter minus select * from mirror_v_$parameter;
to be used inside a procedure, so that it could be used to fetch any returned rows and insert them into another table called alerts_v_$parameter. The intent being that, when something is added to the "alert" table, a trigger can be used to somehow (haven't gotten this far yet) notify my team that there has been a change to the v_$parameter table, and that they can refer to alerts_v_$parameter to see what has been change. I would use some kind of script to run this procedure at a regular interval. And maybe, some day down the line when I understand all this better, manipulate what goes into the alerts_v_$parameter table so that it provides better information such as specifically what column was changed, what was its previous value, etc.
Any advice or pointers?
Thank you for taking the time to read this. Any thoughts will be very appreciated.
I would create a table based on the exact structure of v_$parameter with an additional timestamp column for "last_update", and periodically (via DBMS_Scheduler) merge into it any changes from the real v_$parameter table and capture the timestamp of any detected change.
You might also populate a history table at the same time, either using triggers on update of your table or with SQL.
PL/SQL is unlikely to be required, except as a procedural wrapper to the SQL code.
Examples of Merge are in the documentation here: http://docs.oracle.com/cd/E11882_01/server.112/e26088/statements_9016.htm#SQLRF01606
I have ORM setup and working with Oracle on an existing database and have been able to get inserts to work when I access the sequence but because triggers were used in the original application the sequence skips a number.
Is there a way to get ORM to use the trigger?
Disabling the trigger is not an option since it is used by the existing app and cannot be disabled during migration.
component persistent="true" table="table_name" schema="schema_name" {
property name="table_id" column="table_id" fieldtype="id" generator="sequence" sequence="schema_name.sequence_name";
...
}
Triggers are not accessible program units. The only way to "call" a trigger is to execute the appropriate DML against the owning table.
There are two possible resolutions to your problem.
Rewrite the trigger. You say another application still needs the trigger to populate the ID, but you could change the trigger's logic with a conditional....
if :new.id is null then
:new.id := whatever_seq.nextval; --11g syntax for brevity
end if;
This will populate the ID when the other application insert into the table but won't overwrite your value.
Stop worrying. Sequences are merely generators of unique identifiers. The numbers ascend but it really doesn't matter if there are gaps. Unless you are handling billions of rows it is extremely unlikely your sequence will run out of numbers before your applications get retired.
Do you mean that the DB normally assigns an ID, using an insert trigger? That would explain why you're skipping a number. You could try generator="select" which will get hibernate to read the ID back after the insert has occurred (and the trigger has been fired). It's there to handle exactly the situation I think you're describing.
Can I find out when the last INSERT, UPDATE or DELETE statement was performed on a table in an Oracle database and if so, how?
A little background: The Oracle version is 10g. I have a batch application that runs regularly, reads data from a single Oracle table and writes it into a file. I would like to skip this if the data hasn't changed since the last time the job ran.
The application is written in C++ and communicates with Oracle via OCI. It logs into Oracle with a "normal" user, so I can't use any special admin stuff.
Edit: Okay, "Special Admin Stuff" wasn't exactly a good description. What I mean is: I can't do anything besides SELECTing from tables and calling stored procedures. Changing anything about the database itself (like adding triggers), is sadly not an option if want to get it done before 2010.
I'm really late to this party but here's how I did it:
SELECT SCN_TO_TIMESTAMP(MAX(ora_rowscn)) from myTable;
It's close enough for my purposes.
Since you are on 10g, you could potentially use the ORA_ROWSCN pseudocolumn. That gives you an upper bound of the last SCN (system change number) that caused a change in the row. Since this is an increasing sequence, you could store off the maximum ORA_ROWSCN that you've seen and then look only for data with an SCN greater than that.
By default, ORA_ROWSCN is actually maintained at the block level, so a change to any row in a block will change the ORA_ROWSCN for all rows in the block. This is probably quite sufficient if the intention is to minimize the number of rows you process multiple times with no changes if we're talking about "normal" data access patterns. You can rebuild the table with ROWDEPENDENCIES which will cause the ORA_ROWSCN to be tracked at the row level, which gives you more granular information but requires a one-time effort to rebuild the table.
Another option would be to configure something like Change Data Capture (CDC) and to make your OCI application a subscriber to changes to the table, but that also requires a one-time effort to configure CDC.
Ask your DBA about auditing. He can start an audit with a simple command like :
AUDIT INSERT ON user.table
Then you can query the table USER_AUDIT_OBJECT to determine if there has been an insert on your table since the last export.
google for Oracle auditing for more info...
SELECT * FROM all_tab_modifications;
Could you run a checksum of some sort on the result and store that locally? Then when your application queries the database, you can compare its checksum and determine if you should import it?
It looks like you may be able to use the ORA_HASH function to accomplish this.
Update: Another good resource: 10g’s ORA_HASH function to determine if two Oracle tables’ data are equal
Oracle can watch tables for changes and when a change occurs can execute a callback function in PL/SQL or OCI. The callback gets an object that's a collection of tables which changed, and that has a collection of rowid which changed, and the type of action, Ins, upd, del.
So you don't even go to the table, you sit and wait to be called. You'll only go if there are changes to write.
It's called Database Change Notification. It's much simpler than CDC as Justin mentioned, but both require some fancy admin stuff. The good part is that neither of these require changes to the APPLICATION.
The caveat is that CDC is fine for high volume tables, DCN is not.
If the auditing is enabled on the server, just simply use
SELECT *
FROM ALL_TAB_MODIFICATIONS
WHERE TABLE_NAME IN ()
You would need to add a trigger on insert, update, delete that sets a value in another table to sysdate.
When you run application, it would read the value and save it somewhere so that the next time it is run it has a reference to compare.
Would you consider that "Special Admin Stuff"?
It would be better to describe what you're actually doing so you get clearer answers.
How long does the batch process take to write the file? It may be easiest to let it go ahead and then compare the file against a copy of the file from the previous run to see if they are identical.
If any one is still looking for an answer they can use Oracle Database Change Notification feature coming with Oracle 10g. It requires CHANGE NOTIFICATION system privilege. You can register listeners when to trigger a notification back to the application.
Please use the below statement
select * from all_objects ao where ao.OBJECT_TYPE = 'TABLE' and ao.OWNER = 'YOUR_SCHEMA_NAME'