An Empty String Is Not Null

Why Oracle persists in this ridiculously bad design decision is beyond me. An empty string is a STRING of length 0. NULL is not a string at all. Forget philosphical arguments, it doesn’t help in any way to fail to distinguish ” from null. Whoever decided this obviously never had to write any code to work with recordsets returned from the database. I end up putting a single space where I really just wanted an empty string.

Enterprise Library Logging to Oracle Database

When I first needed to log to an Oracle database from the Enterprise Library, I expected it to be a simple matter of running a script against my Oracle database and adding a few lines to my app.config. Thanks to bad decisions on the part of the Enterprise Library designers and problems with ADO.NET, I had to create my own script to create the necessary tables and stored procedures *and* create two classes that derived from two existing classes in Enterprise Library. This post applies to the Jan ’06 version of the Enterprise library. I have not had a chance to check the Apr ’07 edition to see if they now support Oracle directly.

When I first embarked on this incredibly long journey, I looked at the script included in the EntLib project that creates the tables. Unfortunately, it’s T-SQL specific. So, I converted the script to work with Oracle. That wasn’t so bad. I did have to put “timestamp” in double quotes in my Oracle version of WriteLog since its actually an Oracle datatype. But I was able to invoke my procedure directly using PL/SQL code and I foolishly assumed that EntLib would similarly be able to do so from it’s existing FormattedDatabaseTraceListener.

I fired up my test app and clicked the “Log” button that invoked the EntLib logger. Then I looked at the log table but there were no new entries. I added a flatfile listener and ran the app again. This time I was able to see that the EntLib logging system was trying to write logs out to my oracle database, but was getting the following error (which it kindly logged to the trace file):

PLS-00306: wrong number or types of arguments in call to ‘WRITELOG’

So, I double, triple, quadruple check the order, type, and name of the parameters I am passing and everything looks perfect. Finally, I break down and copy the code that invokes the stored procedure from the EntLib class and add an “Exec Stored Proc” button that will allow me to call the stored procedure directly. I get the same error. Now, I am puzzled. I can invoke this procedure from Pl/SQL but I can call it from ADO.Net. Out of desperation, I change the name of the “timestamp” parameter to TimeOf, recompile the stored proc, and things start working. Apparently, ADO.NET/Oracle cannot handle the parameter with the same name as a reserved word.

Now that I know what the problem is, it’s not very easy to fix. I have to create my own dll that extends the Enterprise Library just to change the name of one parameter in a stored procedure call.

Now that you know the background of why its not as easy as just modifying app.config and running a sql script, you can fully appreciate the attachmdents to this post. I will provide an overview of the importants steps of getting this working in your own project.

First, you will need to add references to the following EntLib dlls in the project in which you want to use the BlueCorner.OracleLogSink dll:


Second, you will need to modify your app.config file. You can view the attached project for all the details, but the only-non-intuitve/non-standard part is the type reference:

<add databaseInstanceName="LoggingDb" writeLogStoredProcName="pkg_logger.WriteLog"
addCategoryStoredProcName="pkg_logger.AddCategory" formatter="Text Formatter"
="BlueCorner.OracleLogSink.FormattedOracleDatabaseTraceListenerData, BlueCorner.OracleLogSink"
type="BlueCorner.OracleLogSink.FormattedOracleDatabaseTraceListener, BlueCorner.OracleLogSink"
name="Database Trace Listener" 

Note the “listenerDataType” and “type” attributes. When I first attempted this, I thought I could reuse the FormattedDatabaseTraceListenerData for the listenerDataType because I was not altering the structure of the configuration section, just the implementation of FormattedDatabaseTraceListener. Unfortunately, this did not work. I had to make a copy of FormattedDatabaseTraceListenerData and the only difference was the name of the class and the referenced classes.

Third, just add a reference to BlueCorner.OracleLogSink either as a project or as a built dll.

Fourth, run the attached database script against your database and alter the connectionString section of your app.config appropriately.

I’m not covering any standard connectivity steps like editing tnsnames.ora, etc. If you need help getting to talk to your oracle schema you will need to look elsewhere.

Here are the working demo project and the sql script you will need. Enjoy.

Oracle (PL/SQL) Equivalents for MS SQL Server (T-SQL) Constructs

For the last several months, I have been working primarily with Oracle 8i and 10g databases.  Over the last 10 years, 95% of my work has been with MS SQL server.  The other 5% was with Oracle, but it was limited to simple SELECT statements or calling stored procedures that other people wrote.  You don’t realize how much basic knowledge you take for granted until you get outside of your comfort zone and have to stop and figure out how to do every little thing.  Here’s a list of the top 10 things I wish I had known about Oracle – PL/SQL coming from an MS SQL Server – T-SQL background.

  1. Bind variables versus PL/SQL variables instead of just variables.  Oversimplifying, use “:” in place of “@” when you want a parameterized query.  This is the most awkward and annoying aspect of Oracle compared to MS SQL Server, IMO.  The bottom line is that you can’t very easily copy code from a stored procedure and run it in Toad or SQL Developer.  Nor can you directly assign values to bind variables — you get prompted for them.
  2. You can’t do a SELECT without an INTO inside of a PL/SQL block.  This is really puzzling.  Especially since you can’t have anything but bind variables outside of a PL/SQL block and you can’t programmatically assign values to bind variables.  All of this adds up to being forced to be prompted for bind variable values every time you run a parameterized query in the SQL Worksheet or in Toad.
  3. There’s no built-in Query Analyzer/SSMS Query tool.  There’s an extremely crippled but free version of Toad.  This what I use if I have to work with a pre-10g instance.  There’s Oracle SQL Developer which is what I use if I am working with a 10g instance.  They both are lacking compared to Query Analyzer/SSMS Query window.  You will press ctrl-E and ctrl-R repeatedly with no effect so many times it will make you sick.
  4. DATEADD doesn’t exist.  You have to add fractional days to dates instead.  DATEADD(hour, 1, D) would be D + 1/24.
  5. INT can’t be used for columns.  You use NUMBER instead.  This can be a real pain in ADO.NET because you have to explicitly convert all those NUMBERs to ints unless you want to treat them as decimals.
  6. No IDENTITY columns.  Instead of typing that one word you have to create a completely separate object called a SEQUENCE and you also have to write a trigger.
  7. You can’t have multiple databases on an Oracle instance.  There are just multiple schemas which are really owners.  Public synonyms are used to make objects from different schemas accessible without explicit schema specification. 
  8. The default date format does not include the time part.  You have to “alter session set NLS_DATE_FORMAT=’MM/DD/YYYY HH24:MI’;” to see the time part.
  9. You concatenate strings with the oh-so-intuitive || instead of the obscure + operation.  Alternatively you can use CONCAT.
  10. You can’t PRINT.  There’s a print-like statement, but it only works in SQL*PLUS.  You don’t ever really want to use SQL*PLUS unless you are a massochistic, command-line-loving freak from the past that still uses VI or EMACS.  Actually, there’s a web-based version of SQL*PLUS that’s usable but I like to stay in the SQL Worksheet.

Those are the top 10 — the things I really struggled to understand coming from the MS SQL side of things.  Here are some more that I found useful:

  • sp_help = DESCRIBE
  • You can’t just SELECT without a FROM clause.  You always have to include FROM DUAL.  I still don’t know what “DUAL” is.
  • Getting just the date part of a date value: CONVERT(datetime, CONVERT(varchar(10), GETDATE(), 101)) = trunc(SYSDATE)
  • Just use VARCHAR2 and don’t ask about VARCHAR.
  • You can’t return values from procedures using the RETURN statement.  Use an OUT param instead.
  • In version 8i and earlier, there’s a “rule-based” optimizer.  The rule-based optimizer can suck badly and you may need to force the join order on some of your queries.  You do that with “SELECT /*+ ordered */” (yes, it really is in the comment).
  • The Oracle compiler doesn’t do a good job of telling what’s wrong with your statement.  It can give obscure messages for missing commas and semi-colons.  Don’t forget that you must terminate each statement with a semi-colon.
  • There’s no built-in support for UUIDs.
  • Oracle does not distingish between an empty string and null (which really sucks)

Here are a couple of non-obvious things I learned about Oracle and .NET 2.0:

  • You can’t send multiple SQL statements in a batch using ADO.NET like you can with MSSQL Server
  • You can’t use the ODP.NET with the Enterprise Library
  • You can’t use non-tnsnames.ora connection strings with System.Data.Oracle but you can with ODP

Changing Oracle’s Default Date Format

If you are stuck using Oracle’s SQL Developer like I am (Toad is $800 now!), then don’t suffer with the braindead default date format like I have until recently.  There’s nothing like just seeing the date in dd-mmm-yy format when you are working with hourly or sub-hourly data all the time like I am.  What were they thinking?  Anyway, you can run this once in your SQL worksheet and enter and see dates with times:

alter session set NLS_DATE_FORMAT='MM/DD/YYYY HH24:MI';