Tim Goeke Thomas Lockhart 1998-10-21 Background information originally by Tim Goeke ODBC (Open Database Connectivity) is an abstract API which allows you to write applications which can interoperate with various RDBMS servers. ODBC provides a product-neutral interface between frontend applications and database servers, allowing a user or developer to write applications which are transportable between servers from different manufacturers.. The ODBC API matches up on the backend to an ODBC-compatible data source. This could be anything from a text file to an Oracle or Postgres RDBMS. The backend access come from ODBC drivers, or vendor specifc drivers that allow data access. psqlODBC is such a driver, along with others that are available, such as the OpenLink ODBC drivers. Once you write an ODBC application, you should be able to connect to any back end database, regardless of the vendor, as long as the database schema is the same. For example. you could have MS SQL Server and Postgres servers which have exactly the same data. Using ODBC, your Windows application would make exactly the same calls and the back end data source would look the same (to the Windows app). In the real world, differences in drivers and the level of ODBC support lessens the potential of ODBC: Access, Delphi, and Visual Basic all support ODBC directly. Under C++, such as Visual C++, you can use the C++ ODBC API. In Visual C++, you can use the CRecordSet class, which wraps the ODBC API set within an MFC 4.2 class. This is the easiest route if you are doing Windows C++ development under Windows NT. If I write an application for Postgres can I write it using ODBC calls to the Postgres server, or is that only when another database program like MS SQL Server or Access needs to access the data? The ODBC API is the way to go. For Visual C++ coding you can find out more at Microsoft's web site or in your VC++ docs. Visual Basic and the other RAD tools have Recordset objects that use ODBC directly to access data. Using the data-aware controls, you can quickly link to the ODBC back end database (very quickly). Playing around with MS Access will help you sort this out. Try using File->Get External Data. You'll have to set up a DSN first. ApplixWare has an ODBC database interface supported on at least some platforms. ApplixWare v4.4.2 has been demonstrated under Linux with Postgres v7.0 using the psqlODBC driver contained in the Postgres distribution. The first thing to note about the psqlODBC driver (or any ODBC driver) is that there must exist a driver manager on the system where the ODBC driver is to be used. There exists a freeware ODBC driver for Unix called iodbc which can be obtained from various locations on the Net, including at AS200. Instructions for installing iodbc are beyond the scope of this document, but there is a README that can be found inside the iodbc compressed .shar file that should explain how to get it up and running. Having said that, any driver manager that you can find for your platform should support the psqlODBC driver or any ODBC driver. The Unix configuration files for psqlODBC have recently been extensively reworked to allow for easy building on supported platforms as well as to allow for support of other Unix platforms in the future. The new configuration and build files for the driver should make it a simple process to build the driver on the supported platforms. Currently these include Linux and FreeBSD but we are hoping other users will contribute the necessary information to quickly expand the number of platforms for which the driver can be built. There are actually two separate methods to build the driver depending on how you received it and these differences come down to only where and how to run configure and make. The driver can be built in a standalone, client-only installation, or can be built as a part of the main Postgres distribution. The standalone installation is convenient if you have ODBC client applications on multiple, heterogeneous platforms. The integrated installation is convenient when the target client is the same as the server, or when the client and server have similar runtime configurations. Specifically if you have received the psqlODBC driver as part of the Postgres distribution (from now on referred to as an "integrated" build) then you will configure and make the ODBC driver from the top level source directory of the Postgres distribution along with the rest of its libraries. If you received the driver as a standalone package than you will run configure and make from the directory in which you unpacked the driver source. This installation procedure is appropriate for an integrated installation. Specify the --with-odbc command-line argument for src/configure: % ./configure --with-odbc % make Rebuild the Postgres distribution: % make install Install the ODBC catalog extensions available in PGROOT/contrib/odbc/odbc.sql: % psql -e template1 < $PGROOT/contrib/odbc/odbc.sql where specifying template1 as the target database will ensure that all subsequent new databases will have these same definitions. Once configured, the ODBC driver will be built and installed into the areas defined for the other components of the Postgres system. The installation-wide ODBC configuration file will be placed into the top directory of the Postgres target tree (POSTGRESDIR). This can be overridden from the make command-line as % make ODBCINST=filename install If you have a Postgres installation older than v6.4, you have the original source tree available, and you want to use the newest version of the ODBC driver, then you may want to try this form of installation. Copy the output tar file to your target system and unpack it into a clean directory. From the directory containing the sources, type: % ./configure % make % make POSTGRESDIR=PostgresTopDir install If you would like to install components into different trees, then you can specify various destinations explicitly: % make BINDIR=bindir LIBDIR=libdir HEADERDIR=headerdir ODBCINST=instfile install A standalone installation is not integrated with or built on the normal Postgres distribution. It should be best suited for building the ODBC driver for multiple, heterogeneous clients who do not have a locally-installed Postgres source tree. The default location for libraries and headers for the standalone installation is /usr/local/lib and /usr/local/include/iodbc, respectively. There is another system wide configuration file that gets installed as /share/odbcinst.ini (if /share exists) or as /etc/odbcinst.ini (if /share does not exist). Installation of files into /share or /etc requires system root privileges. Most installation steps for Postgres do not have this requirement, and you can choose another destination which is writable by your non-root Postgres superuser account instead. The standalone installation distribution can be built from the Postgres distribution or may be obtained from Insight Distributors, the current maintainers of the non-Unix sources. Copy the zip or gzipped tarfile to an empty directory. If using the zip package unzip it with the command % unzip -a packagename The -a option is necessary to get rid of DOS CR/LF pairs in the source files. If you have the gzipped tar package than simply run % tar -xzf packagename To create a tar file for a complete standalone installation from the main Postgres source tree: Configure the main Postgres distribution. Create the tar file: % cd interfaces/odbc % make standalone Copy the output tar file to your target system. Be sure to transfer as a binary file if using ftp. Unpack the tar file into a clean directory. Configure the standalone installation: % ./configure The configuration can be done with options: % ./configure --prefix=rootdir --with-odbc=inidir where --prefix installs the libraries and headers in the directories rootdir/lib and rootdir/include/iodbc, and --with-odbc installs odbcinst.ini in the specified directory. Note that both of these options can also be used from the integrated build but be aware that when used in the integrated build --prefix will also apply to the rest of your Postgres installation. --with-odbc applies only to the configuration file odbcinst.ini. Compile and link the source code: % make ODBCINST=instdir You can also override the default location for installation on the 'make' command line. This only applies to the installation of the library and header files. Since the driver needs to know the location of the odbcinst.ini file attempting to override the enviroment variable that specifies its installation directory will probably cause you headaches. It is safest simply to allow the driver to install the odbcinst.ini file in the default directory or the directory you specified on the './configure' command line with --with-odbc. Install the source code: % make POSTGRESDIR=targettree install To override the library and header installation directories separately you need to pass the correct installation variables on the make install command line. These variables are LIBDIR, HEADERDIR and ODBCINST. Overriding POSTGRESDIR on the make command line will cause LIBDIR and HEADERDIR to be rooted at the new directory you specify. ODBCINST is independent of POSTGRESDIR. Here is how you would specify the various destinations explicitly: % make BINDIR=bindir LIBDIR=libdir HEADERDIR=headerdir install For example, typing % make POSTGRESDIR=/opt/psqlodbc install (after you've used ./configure and make) will cause the libraries and headers to be installed in the directories /opt/psqlodbc/lib and /opt/psqlodbc/include/iodbc respectively. The command % make POSTGRESDIR=/opt/psqlodbc HEADERDIR=/usr/local install should cause the libraries to be installed in /opt/psqlodbc/lib and the headers in /usr/local/include/iodbc. If this doesn't work as expected please contact one of the maintainers. ~/.odbc.ini contains user-specified access information for the psqlODBC driver. The file uses conventions typical for Windows Registry files, but despite this restriction can be made to work. The .odbc.ini file has three required sections. The first is [ODBC Data Sources] which is a list of arbitrary names and descriptions for each database you wish to access. The second required section is the Data Source Specification and there will be one of these sections for each database. Each section must be labeled with the name given in [ODBC Data Sources] and must contain the following entries: Driver = POSTGRESDIR/lib/libpsqlodbc.so Database=DatabaseName Servername=localhost Port=5432 Remember that the Postgres database name is usually a single word, without path names of any sort. The Postgres server manages the actual access to the database, and you need only specify the name from the client. Other entries may be inserted to control the format of the display. The third required section is [ODBC] which must contain the InstallDir keyword and which may contain other options. Here is an example .odbc.ini file, showing access information for three databases: [ODBC Data Sources] DataEntry = Read/Write Database QueryOnly = Read-only Database Test = Debugging Database Default = Postgres Stripped [DataEntry] ReadOnly = 0 Servername = localhost Database = Sales [QueryOnly] ReadOnly = 1 Servername = localhost Database = Sales [Test] Debug = 1 CommLog = 1 ReadOnly = 0 Servername = localhost Username = tgl Password = "no$way" Port = 5432 Database = test [Default] Servername = localhost Database = tgl Driver = /opt/postgres/current/lib/libpsqlodbc.so [ODBC] InstallDir = /opt/applix/axdata/axshlib ApplixWare must be configured correctly in order for it to be able to access the Postgres ODBC software drivers. These instructions are for the 4.4.2 release of ApplixWare on Linux. Refer to the Linux Sys Admin on-line book for more detailed information. You must modify axnet.cnf so that elfodbc can find libodbc.so (the ODBC driver manager) shared library. This library is included with the ApplixWare distribution, but axnet.cnf needs to be modified to point to the correct location. As root, edit the file applixroot/applix/axdata/axnet.cnf. At the bottom of axnet.cnf, find the line that starts with #libFor elfodbc /ax/... Change line to read libFor elfodbc applixroot/applix/axdata/axshlib/lib which will tell elfodbc to look in this directory for the ODBC support library. Typically Applix is installed in /opt so the full path would be /opt/applix/axdata/axshlib/lib, but if you have installed Applix somewhere else then change the path accordingly. Create .odbc.ini as described above. You may also want to add the flag TextAsLongVarchar=0 to the database-specific portion of .odbc.ini so that text fields will not be shown as **BLOB**. Bring up Applix Data Select the Postgres database of interest. Select Query->Choose Server. Select ODBC, and click Browse. The database you configured in .odbc.ini should be shown. Make sure that the Host: field is empty (if it is not, axnet will try to contact axnet on another machine to look for the database). Select the database in the box that was launched by Browse, then click OK. Enter username and password in the login identification dialog, and click OK. You should see "Starting elfodbc server" in the lower left corner of the data window. If you get an error dialog box, see the debugging section below. The 'Ready' message will appear in the lower left corner of the data window. This indicates that you can now enter queries. Select a table from Query->Choose tables, and then select Query->Query to access the database. The first 50 or so rows from the table should appear. The following messages can appear while trying to make an ODBC connection through Applix Data: Cannot launch gateway on server elfodbc can't find libodbc.so. Check your axnet.cnf. Error from ODBC Gateway: IM003::[iODBC][Driver Manager]Specified driver could not be loaded libodbc.so cannot find the driver listed in .odbc.ini. Verify the settings. Server: Broken Pipe The driver process has terminated due to some other problem. You might not have an up-to-date version of the Postgres ODBC package. setuid to 256: failed to launch gateway The September release of ApplixWare v4.4.1 (the first release with official ODBC support under Linux) shows problems when usernames exceed eight (8) characters in length. Problem description ontributed by Steve Campbell. Contributed by Steve Campbell on 1998-10-20. The axnet program's security system seems a little suspect. axnet does things on behalf of the user and on a true multiple user system it really should be run with root security (so it can read/write in each user's directory). I would hesitate to recommend this, however, since we have no idea what security holes this creates. One good tool for debugging connection problems uses the Unix system utility strace. Start applixware. Start an strace on the axnet process. For example, if % ps -aucx | grep ax shows cary 10432 0.0 2.6 1740 392 ? S Oct 9 0:00 axnet cary 27883 0.9 31.0 12692 4596 ? S 10:24 0:04 axmain Then run % strace -f -s 1024 -p 10432 Check the strace output. Many of the error messages from ApplixWare go to stderr, but I'm not sure where stderr is sent, so strace is the way to find out. For example, after getting a "Cannot launch gateway on server", I ran strace on axnet and got [pid 27947] open("/usr/lib/libodbc.so", O_RDONLY) = -1 ENOENT (No such file or directory) [pid 27947] open("/lib/libodbc.so", O_RDONLY) = -1 ENOENT (No such file or directory) [pid 27947] write(2, "/usr2/applix/axdata/elfodbc: can't load library 'libodbc.so'\n", 61) = -1 EIO (I/O error) So what is happening is that applix elfodbc is searching for libodbc.so, but it can't find it. That is why axnet.cnf needed to be changed. In order to go through the ApplixWare Data Tutorial, you need to create the sample tables that the Tutorial refers to. The ELF Macro used to create the tables tries to use a NULL condition on many of the database columns, and Postgres does not currently allow this option. To get around this problem, you can do the following: Copy /opt/applix/axdata/eng/Demos/sqldemo.am to a local directory. Edit this local copy of sqldemo.am: Search for 'null_clause = "NULL" Change this to null_clause = "" Start Applix Macro Editor. Open the sqldemo.am file from the Macro Editor. Select File->Compile and Save. Exit Macro Editor. Start Applix Data. Select *->Run Macro Enter the value "sqldemo", then click OK. You should see the progress in the status line of the data window (in the lower left corner). You should now be able to access the demo tables. You can add information about your database login and password to the standard Applix startup macro file. This is an example ~/axhome/macros/login.am file: macro login set_set_system_var@("sql_username@","tgl") set_system_var@("sql_passwd@","no$way") endmacro You should be careful about the file protections on any file containing username and password information. psqlODBC has been built and tested on Linux. There have been reports of success with FreeBSD and with Solaris. There are no known restrictions on the basic code for other platforms which already support Postgres.