odbc help ( PATCH )

[Vladimir Sekissov]

Good day,

ingela> I am not familiar with this driver. But even if it does not implement
ingela> scrollable cursors it should have values for the driver attribute
ingela> SQL_DYNAMIC_CURSOR_ATTRIBUTES1 otherwhise it is not ODBC 3.0
ingela> compliant.  Of course the value of that attribut will reflect that
ingela> scrollable cursors are not supported. And then the erlang ODBC will
ingela> work but return {error,driver_does_not_support_function} for some
ingela> functions. The patch that you propose is really a workaround for a bug
ingela> in the driver. So I think it is the driver that you should patch.  The
ingela> function call SQLGetInfo could fail for other reasons than that
ingela> scrollable cursors are not supported example a memory allocation error
ingela> and that should be consider a disaster and the application should be
ingela> shut down.

As I mentioned native PostgresSQL ODBC is version 2.5 so it is
compliant only with ODBC 2 specification. If  erlang ODBC can work well
with ODBC 2 drivers why it mustn't. My simple patch doesn't affect any
standard application functionality or behavior so it could be the user's
choice to use it with reduced to ODBC 2 abilities or not.

Best Regards,
Vladimir Sekissov

ingela> > olgeni> Looking for clues... I compiled the odbc application (R9B) using
ingela> > olgeni> libiodbc, installed odbcserver in priv/bin by hand, and found a
ingela> > olgeni> working DSN using the sample iodbc's odbctest application. I'm using
ingela> > olgeni> the postgresql driver (7.2.3).
ingela> > olgeni> 
ingela> > 
ingela> > The problem is that PostgreSQL ODBC driver is version 2.5 and knows
ingela> > nothing about scrollable cursors. This patch solves the
ingela> > problem with one small restriction. The followed function calls return
ingela> > {error,driver_does_not_support_function}:
ingela> 
ingela> I am not familiar with this driver. But even if it does not implement
ingela> scrollable cursors it should have values for the driver attribute
ingela> SQL_DYNAMIC_CURSOR_ATTRIBUTES1 otherwhise it is not ODBC 3.0
ingela> compliant.  Of course the value of that attribut will reflect that
ingela> scrollable cursors are not supported. And then the erlang ODBC will
ingela> work but return {error,driver_does_not_support_function} for some
ingela> functions. The patch that you propose is really a workaround for a bug
ingela> in the driver. So I think it is the driver that you should patch.  The
ingela> function call SQLGetInfo could fail for other reasons than that
ingela> scrollable cursors are not supported example a memory allocation error
ingela> and that should be consider a disaster and the application should be
ingela> shut down.
ingela> 
ingela> ---------- Quote from Microsoft doc: ---------------------
ingela> 
ingela> "A driver must return a value for each of the information types
ingela> defined in the tables below. If an information type does not apply to
ingela> the driver or data source, the driver returns one of the values listed
ingela> in the following table.
ingela> 
ingela> Format of *InfoValuePtr                         Returned value
ingela>    Character string ("Y" or "N")                "N"
ingela>    Character string (not "Y" or "N")            Empty string
ingela>    SQLUSMALLINT                                 0
ingela>    SQLUINTEGER bitmask or SQLUINTEGER binary    0L
ingela> 
ingela>    
ingela>    [...]
ingela> 
ingela>    Information Types
ingela> 
ingela>    This section lists the information types supported by
ingela>    SQLGetInfo. Information types are grouped categorically and listed
ingela>    alphabetically. Information types that were added or renamed for
ingela>    ODBC 3.x are also listed.
ingela> 
ingela>    Driver Information
ingela> 
ingela>    The following values of the InfoType argument return information
ingela>    about the ODBC driver, such as the number of active statements, the
ingela>    data source name, and the interface standards compliance level:
ingela> 
ingela>    SQL_ACTIVE_ENVIRONMENTS
ingela>                                                  SQL_GETDATA_EXTENSIONS
ingela>    SQL_ASYNC_MODE
ingela>                                                  SQL_INFO_SCHEMA_VIEWS
ingela>    SQL_BATCH_ROW_COUNT
ingela>                                                  SQL_KEYSET_CURSOR_ATTRIBUTES1
ingela>    SQL_BATCH_SUPPORT
ingela>                                                  SQL_KEYSET_CURSOR_ATTRIBUTES2
ingela>    SQL_DATA_SOURCE_NAME
ingela>                                                  SQL_MAX_ASYNC_CONCURRENT_STATEMENTS
ingela>    SQL_DRIVER_HDBC
ingela>                                                  SQL_MAX_CONCURRENT_ACTIVITIES
ingela>    SQL_DRIVER_HDESC
ingela>                                                  SQL_MAX_DRIVER_CONNECTIONS
ingela>    SQL_DRIVER_HENV
ingela>                                                  SQL_ODBC_INTERFACE_CONFORMANCE
ingela>    SQL_DRIVER_HLIB
ingela>                                                  SQL_ODBC_STANDARD_CLI_CONFORMANCE
ingela>    SQL_DRIVER_HSTMT
ingela>                                                  SQL_ODBC_VER
ingela>    SQL_DRIVER_NAME
ingela>                                                  SQL_PARAM_ARRAY_ROW_COUNTS
ingela>    SQL_DRIVER_ODBC_VER
ingela>                                                  SQL_PARAM_ARRAY_SELECTS
ingela>    SQL_DRIVER_VER
ingela>                                                  SQL_ROW_UPDATES
ingela>    SQL_DYNAMIC_CURSOR_ATTRIBUTES1
ingela>                                                  SQL_SEARCH_PATTERN_ESCAPE
ingela>    SQL_DYNAMIC_CURSOR_ATTRIBUTES2
ingela>                                                  SQL_SERVER_NAME
ingela>    SQL_FORWARD_ONLY_CURSOR_ATTRIBUTES1
ingela>                                                  SQL_STATIC_CURSOR_ATTRIBUTES1
ingela>    SQL_FORWARD_ONLY_CURSOR_ATTRIBUTES2
ingela>                                                  SQL_STATIC_CURSOR_ATTRIBUTES2
ingela>    SQL_FILE_USAGE"
ingela> 
ingela> --------- End quote   ----------------
ingela> 
ingela> > odbc:select(Conn, Pos, N) when Pos = {relative, P} | {absolute, P}
ingela> > odbc:prev(ConnectionReference)
ingela> > 
ingela> > But most databases don't support back scrolling so we can live
ingela> > without it too. All other functionality is ok at least for me.
ingela> Well yes that how it suppose to work. If scrollable cursors are
ingela> supported you should be able to use them. But if not you can still use
ingela> the part of the API that don't use scrollable cursors.
ingela> 
ingela> -- 
ingela> /m.v.h Ingela
ingela> 
ingela> Ericsson AB - OTP team
ingela> 
ingela> 
ingela> 
ingela> 
ingela>