Enterprise Library and PostgreSQL (Npgsql)

  • Thread starter Thread starter Bradley Plett
  • Start date Start date
B

Bradley Plett

I have two questions that I hope I'm posting in the right area. I've
posted in the pgFoundry forums as well, in hopes that someone can
answer these.

I'm using the Npgsql .Net data provider for PostgreSQL
(http://pgfoundry.org/projects/npgsql/).

1) Has anyone already added support for this provider to the
Enterprise Library? If so, where can I get it? If not, how would I
go about it?

2) I am using the Enterprise Library's ExceptionHandling. When my
Npgsql connection fails, the exception handler in ExceptionHandling
blows up. I don't really know if this is a bug that should be
attributed to the Enterprise Library or to the Npgsql. Has anyone run
into this before? I've worked around it for now by modifying
ExceptionFormatter and putting a try..catch around "value =
property.GetValue(e, null);" (around line 175). This works, but I'm
far from certain this is the right way to do it.

Thanks!
Brad.
 
Hello Brad,

Thank you for posting in the MSDN newsgroup.

From your description, you're using the enterprise library to develop your
.net application and when dealing with the PostgreSQL database, you're
wondering how to integrated the npgsql provider with enterprise library's
DAAB. Also, you're getting some other exceptions when the connection to
postgresql fails, correct?

Based on my research, the npgsql managed provider for postgreSQL database
has only provided .net framework 1.1 based version. Therefore, I think your
application is also developing under .net framework 1.1 and the enterprise
library is of version 1.0(2.0 is specfic to .net framework 2.0), correct?

In the enterprise library 1.0, the built-in database provdiers include SQL,
Oracle, DB2 database providers. As for postgreSQL, if you want to integraed
it into the enterprise library daab framework, you need to create a custom
database provider. This require the following work:
===========
Create a new command wrapper that derives from DBCommandWrapper.
Create a new database class that derives from Database.
Additionally, if you want your client code to remain database-agnostic, you
may need to write additional code to perform such tasks as type conversion.
===========

You can find the "Adding a New Database Provider" topic in the
documentation of enterprise library 1.0(the latest version is 2005 June).

As for the second problem you mentioned, what's the detailed behavior you
met when the Npgsql connection fails? Is the actual exception instance
thrown out to front UI? Based on my understanding, the exception handling
block let us define some exception management policy which can control how
to process when encountering some certain types of exception. What's the
underlying exception type it thrown when Npgsql connection fails(I think it
should be a Npgsql specific exception type) and have you explicitly
configured any policy for it(such as None, Notify and rethrow, or replacing
with new type).

Hope this helps.

Sincerely,

Steven Cheng

Microsoft MSDN Online Support Lead



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Actually, I found the database provider code at

This doesn't resolve the second issue, however. Here's the code to
reproduce the problem:

Try
Dim conn As New NpgsqlConnection(connStr)
conn.Open()
...
Catch ex As Exception
Dim rethrow As Boolean = ExceptionPolicy.HandleException(ex,
"General
Policy")
If (rethrow) Then
Throw
End If
End Try

If the connection string is invalid or the database server is
unavailable, the following occurs in
"ExceptionPolicy.HandleException". As I've said, a tiny modification
to the Enterprise Library alleviates the problem, but I'm still not
sure whether that's the right approach.

An unhandled exception of type
'System.Reflection.TargetParameterCountException'
occurred in mscorlib.dll

Additional information: Parameter count mismatch.


Unhandled Exception: System.Reflection.TargetParameterCountException:
Parameter count mismatch.
at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj,
BindingFlags invokeAttr, Binder binder, Object[] parameters,
CultureInfo culture, Boolean isBinderDefault, Assembly caller, Boolean
verifyAccess)
at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj,
BindingFlags invokeAttr, Binder binder, Object[] parameters,
CultureInfo culture, Boolean
verifyAccess)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj,
BindingFlags invokeAttr, Binder binder, Object[] parameters,
CultureInfo culture)
at System.Reflection.MethodBase.Invoke(Object obj, Object[]
parameters)
at System.Reflection.MethodInfo.Invoke(Object obj, Object[]
parameters)
at System.Reflection.RuntimePropertyInfo.GetValue(Object obj,
Object[]
index)
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionFormatter
..WriteReflectionInfo(Exception e) in C:\Program Files\Microsoft
Enterprise Library June
2005\src\ExceptionHandling\ExceptionFormatter.cs:line 174
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionFormatter
..WriteException(Exception e, Exception outerException) in C:\Program
Files\Microsoft Enterprise Library June
2005\src\ExceptionHandling\ExceptionFormatter.cs:line
132
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.TextExceptionForma
tter.WriteException(Exception e, Exception outerException) in
C:\Program Files\Microsoft Enterprise Library June
2005\src\ExceptionHandling\TextExceptionFormatter.cs:line 107
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionFormatter
..Format() in C:\Program Files\Microsoft Enterprise Library June
2005\src\ExceptionHandling\ExceptionFormatter.cs:line 85
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionUtility.F
ormatHandlingException(StringWriter writer, String header, Exception
ex) in C:\Program Files\Microsoft Enterprise Library June
2005\src\ExceptionHandling\ExceptionUtility.cs:line 83
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionUtility.L
ogHandlingException(String policyName, Exception offendingException,
Exception chainException, Exception originalException) in C:\Program
Files\Microsoft Enterprise Library June
2005\src\ExceptionHandling\ExceptionUtility.cs:line 61
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicyEnt
ry.ExecuteHandlerChain(Exception ex, Guid handlingInstanceID) in
C:\Program Files\Microsoft Enterprise Library June
2005\src\ExceptionHandling\ExceptionPolicyEntry.cs:line 109
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicyEnt
ry.Handle(Exception ex) in C:\Program Files\Microsoft Enterprise
Library June 2005\src\ExceptionHandling\ExceptionPolicyEntry.cs:line
54
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicy.Ha
ndleException(Exception ex) in C:\Program Files\Microsoft Enterprise
Library June 2005\src\ExceptionHandling\ExceptionPolicy.cs:line 146
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicy.Ha
ndleException(Exception ex, String policyName, ConfigurationContext
configurationContext) in C:\Program Files\Microsoft Enterprise Library
June 2005\src\ExceptionHandling\ExceptionPolicy.cs:line 107
at
Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicy.Ha
ndleException(Exception ex, String policyName) in C:\Program
Files\Microsoft Enterprise Library June
2005\src\ExceptionHandling\ExceptionPolicy.cs:line 67
at TPApp.ScheduleListener.Listen() in
F:\TPApp\TPAppListeners\ScheduleListener\ScheduleListener.vb:line 38
 
Thanks for your followup,

I noticed that you've defined the "Generic Policy", that's the detailed
setting of this poilcy since it is when the runtime try applying this
policy to handle the exception that cause the error occured.

Sincerely,

Steven Cheng

Microsoft MSDN Online Support Lead
 
I'm sorry, but I simply don't understand what this response means. Are
you saying I should be using a policy with a different name? I went
through all of the setup steps for the policy I used. Are you saying
there's a problem with my configuration?

Brad.
 
Hi Brad,

Sorry for the confusing. Yes, I mean to check whether it is the
configuration error in the Exception Handing policy that cause the problem.
Because the exception callstack indicate that the reflection (method invoke
code) receive incorrect paratmer counts. Have you tried using the same
setting for a different exception type (like the SqlException ...) to see
whether the same error occurs. If not occurs, the problem should also
specific to the Npgsql provider.

Sincerely,

Steven Cheng

Microsoft MSDN Online Support Lead
This posting is provided "AS IS" with no warranties, and confers no rights.
 
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