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New Message on BDOTNET
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From: Sitaraman
Message 4 in Discussion
Hi Agree with Mahesh. it wont work even in the v1.0. In fact, forget execution
continuing till reader1.read. The moment you do a reader2=objcommand.executereader(),
it will throw u an exception with the message "Additional information: There is
already an open DataReader associated with this Connection which must be closed
first." This is because of the validation called internally by the executereader
method,. When the exception happens, check your callstack. it will be as follows
system.data.dll!System.Data.SqlClient.SqlCommand::ValidateCommand(String* method =
"ExecuteReader", bool executing = true) + 0xa8 bytes
system.data.dll!System.Data.SqlClient.SqlCommand::ExecuteReader(System.Data.CommandBehavior
cmdBehavior = Default, System.Data.SqlClient.RunBehavior runBehavior =
ReturnImmediately, bool returnStream = true) + 0x93 bytes
system.data.dll!System.Data.SqlClient.SqlCommand::ExecuteReader() + 0x16 bytes
> Dummy_RowState.exe!Dummy_RowState.Module1.subReadData() Line 198 + 0xb bytes Basic
Dummy_RowState.exe!Dummy_RowState.Module1.main() Line 9 + 0x6 bytes Basic
ExecutReader() calls -> ExecuteReader(System.Data.CommandBehavior ,
System.Data.SqlClient.RunBehavior,bool returnStream ) which in turn calls the ->
ValidateCommand(String* method , bool executing ) The Exception is actually thrown
by the ValidateCommandmethod. This method internally validates for various things like
the whether the sqlcommand.activeconnection is not nothing or the
l_objSQLCommand.activeconnection's state is open or not etc.. It also checks whether
the connection associated already has any other reader open or not. Note that
SQLCommand has a private property , "_activeconnection" which is of connection type,
pointing to the connectuion the command is currently using. The connection object in
turn a friend property, called "reader", which is of SQLDataReader type. This
property will hold a Open SQLDataReader object which is using the connection through
the command object. So in the following code snippet
l_objConnection.Open()
l_objSQLDataReader1 = l_objSQLCommand1.ExecuteReader() While
l_objSQLDataReader1.Read
Console.writeline(l_objSQLDataReader1.GetString(0))
End While
l_objSQLDataReader2 = l_objSQLCommand2.ExecuteReader At the time of
connection open the l_objConnection.Reader property will be null
l_objSQLCommand1.ExecuteReader is executed validatecommand will check for the
l_objSQLCommand1._activeconnection.reader, which is nothing and happily the method
completes After this , the l_objConnection.reader will be made to point to
l_objSQLDataReader1 (coz this is the reader using the connection) We read the data
from l_objSQLDataReader1
Next, the line l_objSQLDataReader2 = l_objSQLCommand2.ExecuteReader is
executed validatecommand will now check for the
l_objSQLCommand2.activeconnection.reader. Note tht the
l_objSQLCommand2.activeconnection is the same as l_objSQLCommand1.activeconnection,
i.e. l_objConnection, coz both share the same connection) Note that in Step 4
the l_objConnection.reader was made to point to SQLDataReader1 and therefore is NOT
nothing So validatecommand will throw an exception which is what you see To
avoid this the code can be modified as l_objConnection.Open()
l_objSQLDataReader1 = l_objSQLCommand1.ExecuteReader() While
l_objSQLDataReader1.Read
print(l_objSQLDataReader1.GetString(0))
End While objSQLDataReader1.close ' Close SQLDataReader1 before
initializing SQLDataReadwer2 as both of them use the same connection.
l_objSQLDataReader2 = l_objSQLCommand2.ExecuteReader Now when the
SQLDataReader1.close is issued, the SQLDataReader.command.activeconnection.Reader is
set to nothing. So the executeReader for the l_objSQLDataReader2 is executed, the
validatecommand does not have any problems and successfully completes... hth
regards, sr
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