<!-- $Header: /cvsroot/pgsql/doc/src/sgml/Attic/odbc.sgml,v 1.23 2001/09/10 21:58:47 petere Exp $ --> <chapter id="odbc"> <docinfo> <authorgroup> <author> <firstname>Tim</firstname> <surname>Goeke</surname> </author> <author> <firstname>Thomas</firstname> <surname>Lockhart</surname> </author> </authorgroup> <date>1998-10-21</date> </docinfo> <title>ODBC Interface</title> <indexterm zone="odbc"> <primary>ODBC</primary> </indexterm> <note> <para> Background information originally by Tim Goeke (<email>tgoeke@xpressway.com</email>) </para> </note> <para> <acronym>ODBC</acronym> (Open Database Connectivity) is an abstract <acronym>API</acronym> that allows you to write applications that can interoperate with various <acronym>RDBMS</acronym> servers. <acronym>ODBC</acronym> provides a product-neutral interface between frontend applications and database servers, allowing a user or developer to write applications that are transportable between servers from different manufacturers.. </para> <sect1 id="odbc-background"> <title>Background</title> <para> The <acronym>ODBC</acronym> <acronym>API</acronym> matches up on the backend to an <acronym>ODBC</acronym>-compatible data source. This could be anything from a text file to an Oracle or <productname>Postgres</productname> <acronym>RDBMS</acronym>. </para> <para> The backend access come from <acronym>ODBC</acronym> drivers, or vendor-specific drivers that allow data access. <productname>psqlODBC</productname> is such a driver, along with others that are available, such as the <productname>OpenLink</productname> <acronym>ODBC</acronym> drivers. </para> <para> Once you write an <acronym>ODBC</acronym> application, you <emphasis>should</emphasis> be able to connect to <emphasis>any</emphasis> back end database, regardless of the vendor, as long as the database schema is the same. </para> <para> For example. you could have <productname>MS SQL Server</productname> and <productname>Postgres</productname> servers that have exactly the same data. Using <acronym>ODBC</acronym>, your Windows application would make exactly the same calls and the back end data source would look the same (to the Windows app). </para> </sect1> <sect1 id="odbc-install"> <title>Installation</title> <para> The first thing to note about the <productname>psqlODBC</> driver (or any <acronym>ODBC</> driver) is that there must exist a <firstterm>driver manager</> on the system where the <acronym>ODBC</> driver is to be used. There exists a free <acronym>ODBC</> driver for Unix called <indexterm><primary>iODBC</primary></indexterm> <productname>iODBC</> which can be obtained via <ulink url="http://www.iodbc.org">http://www.iodbc.org</ulink>. Instructions for installing <productname>iODBC</> are contained in the <productname>iODBC</> distribution. Having said that, any driver manager that you can find for your platform should support the <productname>psqlODBC</> driver, or any other <acronym>ODBC</> driver for that matter. </para> <para> To install <productname>psqlODBC</> you simply need to supply the <option>--enable-odbc</> option to the <filename>configure</> script when you are building the entire <productname>PostgreSQL</> distribution. The library and header files will then automatically be built and installed with the rest of the programs. If you forget that option or want to build the ODBC driver later you can change into the directory <filename>src/interfaces/odbc</> and do <literal>make</> and <literal>make install</> there. </para> <para> The installation-wide configuration file <filename>odbcinst.ini</> will be installed into the directory <filename>/usr/local/pgsql/etc/</>, or equivalent, depending on what <option>--prefix</> and/or <option>--sysconfdir</> options you supplied to <filename>configure</>. Since this file can also be shared between different <acronym>ODBC</> drivers you can also install it in a shared location. To do that, override the location of this file with the <option>--with-odbcinst</> option. </para> <para> Additionally, you should install the ODBC catalog extensions. That will provide a number of functions mandated by the ODBC standard that are not supplied by <productname>PostgreSQL</> by default. The file <filename>/usr/local/pgsql/share/odbc.sql</> (in the default installation layout) contains the appropriate definitions, which you can install as follows: <programlisting> psql -d template1 -f <replaceable>LOCATION</>/odbc.sql </programlisting> where specifying <literal>template1</literal> as the target database will ensure that all subsequent new databases will have these same definitions. </para> <sect2> <title>Supported Platforms</title> <para> <productname>psqlODBC</productname> has been built and tested on <systemitem class="osname">Linux</>. There have been reports of success with <systemitem class="osname">FreeBSD</> and with <systemitem class="osname">Solaris</>. There are no known restrictions on the basic code for other platforms which already support <productname>Postgres</productname>. </para> </sect2> </sect1> <sect1 id="odbc-config"> <title>Configuration Files</title> <para> <filename>~/.odbc.ini</filename> contains user-specified access information for the <productname>psqlODBC</productname> driver. The file uses conventions typical for <productname>Windows</productname> Registry files, but despite this restriction can be made to work. </para> <para> The <filename>.odbc.ini</filename> file has three required sections. The first is <literal>[ODBC Data Sources]</literal> 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 <literal>[ODBC Data Sources]</literal> and must contain the following entries: <programlisting> Driver = <replaceable>prefix</replaceable>/lib/libpsqlodbc.so Database=<replaceable>DatabaseName</replaceable> Servername=localhost Port=5432 </programlisting> <tip> <para> Remember that the <productname>Postgres</productname> database name is usually a single word, without path names of any sort. The <productname>Postgres</productname> server manages the actual access to the database, and you need only specify the name from the client. </para> </tip> Other entries may be inserted to control the format of the display. The third required section is <literal>[ODBC]</literal> which must contain the <literal>InstallDir</literal> keyword and which may contain other options. </para> <para> Here is an example <filename>.odbc.ini</filename> file, showing access information for three databases: <programlisting> [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 </programlisting> </para> </sect1> <sect1 id="odbc-windows"> <title><productname>Windows</productname> Applications</title> <para> In the real world, differences in drivers and the level of <acronym>ODBC</acronym> support lessens the potential of <acronym>ODBC</acronym>: <itemizedlist spacing="compact" mark="bullet"> <listitem> <para> Access, Delphi, and Visual Basic all support <acronym>ODBC</acronym> directly. </para> </listitem> <listitem> <para> Under C++, such as Visual C++, you can use the C++ <acronym>ODBC</acronym> <acronym>API</acronym>. </para> </listitem> <listitem> <para> In Visual C++, you can use the <classname>CRecordSet</classname> class, which wraps the <acronym>ODBC</acronym> <acronym>API</acronym> set within an <application>MFC</application> 4.2 class. This is the easiest route if you are doing Windows C++ development under Windows NT. </para> </listitem> </itemizedlist> </para> <sect2> <title>Writing Applications</title> <para> <quote> If I write an application for <productname>Postgres</productname> can I write it using <acronym>ODBC</acronym> calls to the <productname>Postgres</productname> server, or is that only when another database program like MS SQL Server or Access needs to access the data? </quote> </para> <para> The <acronym>ODBC</acronym> <acronym>API</acronym> is the way to go. For <productname>Visual C++</productname> coding you can find out more at Microsoft's web site or in your <productname>VC++</productname> docs. </para> <para> Visual Basic and the other <acronym>RAD</acronym> tools have <classname>Recordset</classname> objects that use <acronym>ODBC</acronym> directly to access data. Using the data-aware controls, you can quickly link to the <acronym>ODBC</acronym> back end database (<emphasis>very</emphasis> quickly). </para> <para> Playing around with MS Access will help you sort this out. Try using <literal>File->Get External Data</literal>. </para> <tip> <para> You'll have to set up a <acronym>DSN</acronym> first. </para> </tip> </sect2> </sect1> <sect1 id="odbc-applixware"> <title><application>ApplixWare</application></title> <indexterm zone="odbc-applixware"> <primary>ApplixWare</primary> </indexterm> <para> <productname>ApplixWare</productname> has an <acronym>ODBC</acronym> database interface supported on at least some platforms. <productname>ApplixWare</productname> 4.4.2 has been demonstrated under Linux with <productname>Postgres</productname> 7.0 using the <productname>psqlODBC</productname> driver contained in the <productname>Postgres</productname> distribution. </para> <sect2> <title>Configuration</title> <para> <productname>ApplixWare</productname> must be configured correctly in order for it to be able to access the <productname>Postgres</productname> <acronym>ODBC</acronym> software drivers. </para> <procedure> <title>Enabling <application>ApplixWare</application> Database Access</title> <para> These instructions are for the <literal>4.4.2</literal> release of <productname>ApplixWare</productname> on <productname>Linux</productname>. Refer to the <citetitle>Linux Sys Admin</citetitle> on-line book for more detailed information. </para> <step performance="required"> <para> You must modify <filename>axnet.cnf</filename> so that <filename>elfodbc</filename> can find <filename>libodbc.so</filename> (the <acronym>ODBC</acronym> driver manager) shared library. This library is included with the <application>ApplixWare</application> distribution, but <filename>axnet.cnf</filename> needs to be modified to point to the correct location. </para> <para> As root, edit the file <filename><replaceable>applixroot</replaceable>/applix/axdata/axnet.cnf</filename>. </para> <substeps> <step performance="required"> <para> At the bottom of <filename>axnet.cnf</filename>, find the line that starts with <programlisting> #libFor elfodbc /ax/<replaceable>...</replaceable> </programlisting> </para> </step> <step performance="required"> <para> Change line to read <programlisting> libFor elfodbc <replaceable>applixroot</replaceable>/applix/axdata/axshlib/lib </programlisting> which will tell <literal>elfodbc</literal> to look in this directory for the <acronym>ODBC</acronym> support library. Typically <productname>Applix</productname> is installed in <filename>/opt</filename> so the full path would be <filename>/opt/applix/axdata/axshlib/lib</filename>, but if you have installed <productname>Applix</productname> somewhere else then change the path accordingly. </para> </step> </substeps> </step> <step performance="required"> <para> Create <filename>.odbc.ini</filename> as described above. You may also want to add the flag <programlisting> TextAsLongVarchar=0 </programlisting> to the database-specific portion of <filename>.odbc.ini</filename> so that text fields will not be shown as <literal>**BLOB**</literal>. </para> </step> </procedure> <procedure> <title>Testing <application>ApplixWare</application> ODBC Connections</title> <step performance="required"> <para> Bring up <application>Applix Data</application> </para> </step> <step performance="required"> <para> Select the <productname>Postgres</productname> database of interest. </para> <substeps> <step performance="required"> <para> Select <command>Query->Choose Server</command>. </para> </step> <step performance="required"> <para> Select <acronym>ODBC</acronym>, and click <command>Browse</command>. The database you configured in <filename>.odbc.ini</filename> should be shown. Make sure that the <option>Host: field</option> is empty (if it is not, <literal>axnet</> will try to contact <literal>axnet</> on another machine to look for the database). </para> </step> <step performance="required"> <para> Select the database in the box that was launched by <command>Browse</command>, then click <command>OK</command>. </para> </step> <step performance="required"> <para> Enter user name and password in the login identification dialog, and click <command>OK</command>. </para> </step> </substeps> <para> You should see <literal>Starting elfodbc server</literal> in the lower left corner of the data window. If you get an error dialog box, see the debugging section below. </para> </step> <step performance="required"> <para> The 'Ready' message will appear in the lower left corner of the data window. This indicates that you can now enter queries. </para> </step> <step performance="required"> <para> 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. </para> </step> </procedure> </sect2> <sect2> <title>Common Problems</title> <para> The following messages can appear while trying to make an <acronym>ODBC</acronym> connection through <productname>Applix Data</productname>: <variablelist> <varlistentry> <term> <computeroutput>Cannot launch gateway on server</computeroutput> </term> <listitem> <para> <literal>elfodbc</literal> can't find <filename>libodbc.so</filename>. Check your <filename>axnet.cnf</filename>. </para> </listitem> </varlistentry> <varlistentry> <term><computeroutput> Error from ODBC Gateway: IM003::[iODBC][Driver Manager]Specified driver could not be loaded</computeroutput> </term> <listitem> <para> <filename>libodbc.so</filename> cannot find the driver listed in <filename>.odbc.ini</filename>. Verify the settings. </para> </listitem> </varlistentry> <varlistentry> <term> <computeroutput>Server: Broken Pipe</computeroutput> </term> <listitem> <para> The driver process has terminated due to some other problem. You might not have an up-to-date version of the <productname>Postgres</productname> <acronym>ODBC</acronym> package. </para> </listitem> </varlistentry> <varlistentry> <term> <computeroutput>setuid to 256: failed to launch gateway</computeroutput> </term> <listitem> <para> The September release of <application>ApplixWare</application> v4.4.1 (the first release with official <acronym>ODBC</acronym> support under Linux) shows problems when user names exceed eight (8) characters in length. Problem description contributed by Steve Campbell (<email>scampbell@lear.com</email>). </para> </listitem> </varlistentry> </variablelist> </para> <para> <note> <title>Author</title> <para> Contributed by Steve Campbell (<email>scampbell@lear.com</email>), 1998-10-20 </para> </note> The <application>axnet</application> program's security system seems a little suspect. <application>axnet</application> 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. </para> </sect2> <sect2> <title>Debugging <application>ApplixWare</application> ODBC Connections</title> <para> One good tool for debugging connection problems uses the Unix system utility <application>strace</application>. </para> <procedure> <title>Debugging with <command>strace</command></title> <step performance="required"> <para> Start <application>ApplixWare</application>. </para> </step> <step performance="required"> <para> Start an <application>strace</application> on the <literal>axnet</literal> process. For example, if <programlisting> % ps -aucx | grep ax </programlisting> shows <programlisting> 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 </programlisting> </para> <para> Then run <programlisting> % strace -f -s 1024 -p 10432 </programlisting> </para> </step> <step performance="required"> <para> Check the <command>strace</command> output. </para> <note> <title>Note from Cary</title> <para> Many of the error messages from <productname>ApplixWare</productname> go to <filename>stderr</filename>, but I'm not sure where <filename>stderr</filename> is sent, so <application>strace</application> is the way to find out. </para> </note> </step> </procedure> <para> For example, after getting a <literal>Cannot launch gateway on server</literal>, I ran <command>strace</command> on <literal>axnet</literal> and got <programlisting> [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) </programlisting> So what is happening is that <literal>applix elfodbc</literal> is searching for <filename>libodbc.so</filename>, but it cannot find it. That is why <filename>axnet.cnf</filename> needed to be changed. </para> </sect2> <sect2> <title>Running the <application>ApplixWare</application> Demo</title> <para> In order to go through the <citetitle>ApplixWare Data Tutorial</citetitle>, 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 <productname>Postgres</productname> does not currently allow this option. </para> <para> To get around this problem, you can do the following: </para> <procedure> <title>Modifying the <application>ApplixWare</application> Demo</title> <step performance="required"> <para> Copy <filename>/opt/applix/axdata/eng/Demos/sqldemo.am</filename> to a local directory. </para> </step> <step performance="required"> <para> Edit this local copy of <filename>sqldemo.am</filename>: </para> <substeps> <step performance="required"> <para> Search for 'null_clause = "NULL" </para> </step> <step performance="required"> <para> Change this to null_clause = "" </para> </step> </substeps> </step> <step performance="required"> <para> Start <application>Applix Macro Editor</application>. </para> </step> <step performance="required"> <para> Open the <filename>sqldemo.am</filename> file from the <application>Macro Editor</application>. </para> </step> <step performance="required"> <para> Select <command>File->Compile and Save</command>. </para> </step> <step performance="required"> <para> Exit <application>Macro Editor</application>. </para> </step> <step performance="required"> <para> Start <application>Applix Data</application>. </para> </step> <step performance="required"> <para> Select <command>*->Run Macro</command> </para> </step> <step performance="required"> <para> Enter the value "<literal>sqldemo</literal>", then click <command>OK</command>. </para> <para> You should see the progress in the status line of the data window (in the lower left corner). </para> </step> <step performance="required"> <para> You should now be able to access the demo tables. </para> </step> </procedure> </sect2> <sect2> <title>Useful Macros</title> <para> You can add information about your database login and password to the standard <application>Applix</application> start-up macro file. This is an example <filename>~/axhome/macros/login.am</filename> file: <programlisting> macro login set_set_system_var@("sql_username@","tgl") set_system_var@("sql_passwd@","no$way") endmacro </programlisting> <caution> <para> You should be careful about the file protections on any file containing user name and password information. </para> </caution> </para> </sect2> </sect1> </chapter> <!-- Keep this comment at the end of the file Local variables: mode:sgml sgml-omittag:t sgml-shorttag:t sgml-minimize-attributes:nil sgml-always-quote-attributes:t sgml-indent-step:1 sgml-indent-data:t sgml-parent-document:nil sgml-default-dtd-file:"./reference.ced" sgml-exposed-tags:nil sgml-local-catalogs:("/usr/lib/sgml/catalog") sgml-local-ecat-files:nil End: -->