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 <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>
    In order to make use of an <acronym>ODBC</> driver there must
    exist a <firstterm>driver manager</> on the system where the
    <acronym>ODBC</> driver is to be used.  There are two free
    <acronym>ODBC</> driver managers for Unix-like operating systems
    known to us: <indexterm><primary>iODBC</primary></indexterm>
    <ulink url="http://www.iodbc.org"><productname>iODBC</></ulink>
    and <indexterm><primary>unixODBC</primary></indexterm> <ulink
    url="http://www.unixodbc.org"><productname>unixODBC</></ulink>.
    Instructions for installing these driver managers are to be found
    in the respective distribution.  Software that provides database
    access through <acronym>ODBC</acronym> should provide its own
    driver manager (which may well be one of these two).  Having said
    that, any driver manager that you can find for your platform
    should support the <productname>PostgreSQL</> <acronym>ODBC</>
    driver, or any other <acronym>ODBC</> driver for that matter.
   </para>

   <note>
    <para>
     The <productname>unixODBC</> distribution ships with a
     <productname>PostgreSQL</> <acronym>ODBC</> driver of its own,
     which is similar to the one contained in the
     <productname>PostgreSQL</> distribution.  It is up to you which
     one you want to use.  We plan to coordinate the development of
     both drivers better in the future.
    </para>
   </note>

   <para>
    To install the <acronym>ODBC</> 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 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>
    It is also possible to build the driver to be specifically tuned
    for use with <productname>iODBC</> or <productname>unixODBC</>.
    This means in particular that the driver will use the driver
    manager's routines to process the configuration files, which is
    probably desirable since it creates a more consistent
    <acronym>ODBC</> environment on your system.  If you want to do
    that, then supply the <filename>configure</> options
    <option>--with-iodbc</> or <option>--with-unixodbc</> (but not
    both).
   </para>

   <para>
    If you build a <quote>stand-alone</quote> driver (not tied to
    <productname>iODBC</> or <productname>unixODBC</>), then you can
    specify where the driver should look for the configuration file
    <filename>odbcinst.ini</>.  By default it will be the directory
    <filename>/usr/local/pgsql/etc/</>, or equivalent, depending on
    what <option>--prefix</> and/or <option>--sysconfdir</> options
    you supplied to <filename>configure</>.  To select a specific
    location outside the <productname>PostgreSQL</> installation
    layout, use the <option>--with-odbcinst</> option.  To be most
    useful, it should be arranged that the driver and the driver
    manager read the same configuration file.
   </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.  If for any reason you want to remove
    these functions again, run the file
    <filename>odbc-drop.sql</filename> through
    <command>psql</command>.
   </para>
  </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 <literal>Ready</literal> 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 <literal>null_clause = "NULL"</literal>.
	</para>
       </step>

       <step performance="required">
	<para>
	 Change this to <literal>null_clause = ""</literal>.
	</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>

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