Closing DataReader inside of Try{}Catch{}

[Jeff User]

Hi all
I am using an OleDbDataReader.
I need to establish and then keep the connection that I use, but I do
not need to keep the data reader, after this operation is over.

Therefore, regardless of failure or not, I need to close the data
reader. So, in trying to practice good habits (and if I dont it causes
an error the next time around) I close the reader before exiting this
procedure.
This is fine until I need to handle errors. So, I implement
try{}catch{} to handle if an error occurs. If an error, I also need to
close reader before exiting.

Although I am setting the data reader in a Try statement, I can not
close it in the Catch statement because of compile error:
use of unassigned local variable 'LocalReader'

How can I handle this?
Here is the basic idea:

public string[] select(string SqlStatement)
{
OleDbDataReader LocalReader;
try
{
LocalReader = executeReader(SqlStatement);
while(LocalReader.Read())
{
... do some data stuff here...
}
}
catch(Exception er)
{
LocalReader.Close(); // unassigned local variable here
.... throw error, or whatever...
}
LocalReader.Close(); //this close is OK
return sResultArray; // or whatever...
}

private System.Data.OleDb.OleDbDataReader executeReader (string
sqlStmnt)
{
// Uses server connection that is extablished elsewhere
// prior to executing operations on db
System.Data.OleDb.OleDbCommand cmd = new
OleDbCommand (sqlStmnt, this.get_servconn());

System.Data.OleDb.OleDbDataReader rdr = cmd.ExecuteReader();
return rdr;
}

This code works without the try-Catch statements but when there are
errors such as table not found, etc.., I need to close the reader
before trying again.

I have read several basic data access articles but none show how to
handle closing in case of error.

Thanks
Jeff

 

[Nicholas Paldino [.NET/C# MVP]]

Jeff,

Just assign the LocalReader variable to null in the declaration, and the
code should compile fine.

Hope this helps.

 

[John Richardson]

you should put it in a "finally" block after the catch.
Or use it in a Using block, which is what I usually prefer, since it is a
little nicer to read.

 

[Daniel O'Connell [C# MVP]]

Hi all
I am using an OleDbDataReader.
I need to establish and then keep the connection that I use, but I do
not need to keep the data reader, after this operation is over.

Therefore, regardless of failure or not, I need to close the data
reader. So, in trying to practice good habits (and if I dont it causes
an error the next time around) I close the reader before exiting this
procedure.
This is fine until I need to handle errors. So, I implement
try{}catch{} to handle if an error occurs. If an error, I also need to
close reader before exiting.

Although I am setting the data reader in a Try statement, I can not
close it in the Catch statement because of compile error:
use of unassigned local variable 'LocalReader'

How can I handle this?
Here is the basic idea:

public string[] select(string SqlStatement)
{
OleDbDataReader LocalReader;
try
{
LocalReader = executeReader(SqlStatement);
while(LocalReader.Read())
{
... do some data stuff here...
}
}
catch(Exception er)
{
LocalReader.Close(); // unassigned local variable here
.... throw error, or whatever...
}
LocalReader.Close(); //this close is OK
return sResultArray; // or whatever...
}

Try setting LocalReader to null at initalization time and then use an if
statement in your catch:

OleDbDataReader LocalReader = null;
try
{

}
catch
{
if (LocalReader != null)
LocalReader.Close();
}

 

[Jeff User]

Thanks guys

Setting it to null when declaring it solved the problem!

Jeff