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There are more efficient ways to audit information in the database than via a customwritten trigger For example, you can use the DBMS_FGA package or just the AUDIT command itself A question that application developers often pose to me is, How can I log errors in my PL/SQL routines in a manner that will persist, even when my PL/SQL routines' work is rolled back Earlier, we described how PL/SQL statements are atomic they either completely succeed or completely fail If we logged an error in our PL/SQL routines, by default our logged error information would roll back when Oracle rolled back our statement Autonomous transactions allow us to change that behavior, to have our error logging information persist even while the rest of the partial work is rolled back.

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let dataAdapter = new SqlDataAdapter() let buildDataSet conn queryString = dataAdapter.SelectCommand <- new SqlCommand(queryString, conn) let dataSet = new DataSet() // This line is needed to configure the command let _ = new SqlCommandBuilder(dataAdapter) dataAdapter.Fill(dataSet) |> ignore // ignore the number of records returned dataSet The inferred types are as follows: val dataAdapter : SqlDataAdapter val buildDataSet : SqlConnection -> string -> DataSet When setting up the data adapter, we initialize its SelectCommand property to the query string that was passed as an argument. This SQL query will be used to populate the DataSet when the Fill method is called. The somewhat mysterious line let _ = new SqlCommandBuilder(dataAdapter) creates a command builder object, which has the side effect of building the INSERT, UPDATE, and DELETE commands automatically from the query in SelectCommand, making the dataset capable of persisting changes. Also, note that we do not have to worry about opening or closing connections, because this is all taken care of with the data adapter; all we need is the connection object itself. let dataSet = buildDataSet conn "SELECT EmpID, FirstName, LastName, Birthday from Employees" The resulting DataSet will contain a single table that we obtain by index and print its content. This table is assembled based on the query and contains the columns that were part of the SELECT statement. let table = dataSet.Tables.Item(0) for row in table.Rows do printfn "%O, %O - %O" (row.Item "LastName") (row.Item "FirstName") (row.Item "Birthday") When run in F# Interactive, this produces the following output: Smith, Joe - 14/02/1965 00:00:00 Jones, Mary - 15/09/1985 00:00:00

Let s start by setting up a simple error logging table to use; we ll record the timestamp of the error, the error message, and the PL/SQL error stack (for pinpointing where the error emanated from):.

ops$tkyte%ORA11GR2> create table error_log 2 ( ts timestamp, 3 err1 clob, 4 err2 clob ) 5 / Table created. Now we need the PL/SQL routine to log errors into this table. We can use this small example: ops$tkyte%ORA11GR2> create or replace 2 procedure log_error 3 ( p_err1 in varchar2, p_err2 in varchar2 ) 4 as 5 pragma autonomous_transaction; 6 begin 7 insert into error_log( ts, err1, err2 ) 8 values ( systimestamp, p_err1, p_err2 ); 9 commit; 10 end; 11 / Procedure created. The magic of this routine is on line 5 where we used the pragma autonomous_transaction directive to inform PL/SQL that we want this subroutine to start a new transaction, perform some work in it, and commit it without affecting any other transaction currently in process. The COMMIT on line 9 can affect only the SQL performed by this LOG_ERROR procedure. Now let s test it out. To make it interesting, we ll create a couple of procedures that will call each other: ops$tkyte%ORA11GR2> create table t ( x int check (x>0) ); Table created. ops$tkyte%ORA11GR2> create or replace procedure p1( p_n in number ) 2 as 3 begin 4 -- some code here 5 insert into t (x) values ( p_n ); 6 end; 7 / Procedure created. ops$tkyte%ORA11GR2> create or replace procedure p2( p_n in number ) 2 as 3 begin 4 -- code 5 -- code 6 p1(p_n); 7 end; 8 / Procedure created.

You can refer to each column of a row by the same field name that was used in the SELECT query. Adding a new row to table is treated similarly: let row = table.NewRow() row.Item("EmpID") <- 1003 row.Item("FirstName") <- "Eve" row.Item("LastName") <- "Smith" row.Item("Birthday") <- System.DateTime.Today table.Rows.Add row dataAdapter.Update(dataSet) |> ignore // ignore the number of affected rows Repeating the SQL query from the previous section reveals the addition of the new entry to the database table: > query();; val it : seq<string * System.DateTime> = seq [("Joe", 14/02/1965 00:00:00); ("Mary", 15/09/1985 00:00:00); ("Eve", 27/09/2007 00:00:00)] Note that we utilize the INSERT statement that was built by the command builder object based on the selection query. Using untyped datasets is a great way to execute dynamic queries and to provide ad hoc access to your data. On the other hand, the lack of strong typing means that it suffers from possible type mismatches or incorrect field names.