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<!doctype linuxdoc system>
<article>
<title>MySQLdb FAQ
<author>Andy Dustman
<date>$Id$
<sect>Compiling <tt/_mysqlmodule.so/
<P>Here are some common errors that happen during the build.
This section covers UNIX/Linux problems only, as I don't do Windows.
<tt/.so/ is a dynamically loading library on Linux and most other UNIX
variants; a few use extensions other than <tt/.so/. Windows probably
uses <tt/.dll/.
<sect1>ImportError: libmysqlclient.so.6: cannot open shared object file:
No such file or directory
<P>
You have dynamic MySQL libraries, and by default, your compiler links
<tt/_mysqlmodule.so/ against these, but these are not on your loader path
when you start Python.
You have two basic options:
<p>
<enum>
<item>
Modify the compiler flags in Setup so that it links against the static
library. Probably <tt/-static/ will do this for gcc/egcs; YMMV for
other C compilers.
<item>
Change your system environment so that the MySQL libraries are on
your loader path. With Linux, you can modify <tt>/etc/ld.so.conf</tt> (see
<tt/man ldconfig/ for more details) or you can add to or create the
<tt/LD_LIBRARY_PATH/ environment variable before starting Python, i.e.
<p><code>
LD_LIBRARY_PATH=/path/to/mysql/libs python ... # Bourne-ish shell
</code>
</enum>
<sect1>ImportError: ./_mysqlmodule.so: undefined symbol: PyLong_FromUnsignedLongLong
<p>
<tt/PyLong_FromUnsignedLongLong()/ first appears in Python 1.5.2, so you are
linking against an earlier version. You may also have more than one version
installed. Get Python 1.5.2 from your vendor or python.org.
<sect1>./_mysqlmodule.c:33: mysql.h: No such file or directory
<P>The include path (-I) to your MySQL include files is wrong; modify
Setup. OR: You don't have the MySQL development stuff loaded. If you
are using the Red Hat RPMs, you need the <tt/MySQL-devel/ RPM to compile
<tt/_mysqlmodule.so/. However, if you link against the static MySQL
libraries (see above), you can install <tt/_mysqlmodule.so/ on a system
that does not have the MySQL client libraries (<tt/libmysqlclient/).
<sect1>I'm using Windows...
<P>Say no more.
<P>There is a <tt/compile.py/ script which supposedly gets the job done
for Windows, but I can't test it.
</sect1>
<sect>
Trouble with ZMySQLDA
<p>There are a few tricks to getting Zope's ZMySQLDA to work with
<tt/_mysql/. But it ain't that hard, really.
Also see the
<htmlurl url="http://www.zope.org/Members/alanpog/zmysqlda_steps"
name="ZMySQLDA HOWTO">.
<sect1>Building ZMySQLDA
<p>
The basic steps are:
<enum>
<item>Install MySQLdb first, so that it's on your <tt/PYTHONPATH/
and Zope can find it.
<item>Untar the ZMySQLDA tarball (available from
<htmlurl url="http://www.zope.org/Members/MikeP/ZMySQLDA"
name="zope.org">).
<item>Patch it with the ZMySQLDA.patch included with the MySQLdb
distribution. In the directory that you did the untar,
<code>
patch -p1 &lt;/path/to/ZMySQLDA.patch
</code>
<item>If you do a make, which is what the ZMySQLDA instructions
tell you, it will try to compile the older
MySQLmodule, which you don't need. Ignore stuff like:
<code>
./MySQLmodule.c: In function `pythonify_row':
./MySQLmodule.c:238: warning: assignment from incompatible pointer type
./MySQLmodule.c: In function `pythonify_res_fields':
./MySQLmodule.c:384: invalid lvalue in unary `&'
./MySQLmodule.c: In function `STH_fetchdict':
./MySQLmodule.c:1125: invalid lvalue in unary `&'
./MySQLmodule.c:1147: invalid lvalue in unary `&'
make: *** [MySQLmodule.o] Error 1
</code>
MySQLmodule.c doesn't compile against
MySQL-3.22 without patches. Which is why MySQLdb exists...
<item>Restart Zope. You should have a ZMySQLDA Product in the
Control Panel.
</enum>
<sect1>How do I use it?
<P>I'm not the best person to ask. There are two main steps to getting
started.
<enum>
<item>Create a ZMySQLDA Connection object somewhere.
<item>The connect string syntax is "database@host user password".
If the database is on the same host as the Zope server, you can leave
out @host. You might be able to leave off user and password as well,
depending on your GRANT tables. Whether or not this is a good idea is
another question.
<item>You're on your own. I recommend reading the
<htmlurl url="http://www.zope.org/Documentation/Guides/ZSQL-HTML/ZSQL.html"
name="Z SQL Method's User Guide"> and maybe
<htmlurl url="http://www.zope.org/SiteIndex/search?text_content=sql"
name="searching the Zope website for SQL">.
</enum>
<sect>Using MySQLdb
<p>
MySQLdb is a
<htmlurl url="http://www.python.org/topics/database/DatabaseAPI-2.0.html"
name="Python Database API Specification 2.0"> database module, so you
should be familiar with the spec. Deviations from the spec are documented in the
<htmlurl url="http://starship.python.net/crew/adustman/MySQLdb.html"
name="MySQLdb documentation">.
<sect1>What do I do if I am completely clueless?
<p>Get a clue. Clues have been provided in the <tt/examples/ directory
of the MySQLdb distribution.
<sect1>No, I mean <em/really/ clueless!
<p>Okay, it goes something like this:
<enum>
<item>
Import MySQLdb.
<item>
Create a Connection object.
<item>
Create a Cursor object.
<item>
Execute your query on the Cursor object.
<item>
If your query returns rows, you can use the Cursor object to fetch them.
<item>
Rinse, lather, repeat.
</enum>
Example:
<code>
import MySQLdb
db = MySQLdb.connect(db='mydb',user='myuser',passwd='mypasswd')
c = db.cursor()
c.execute(myquery)
results = c.fetchall()
</code>
<sect1>But MySQL doesn't have cursors!
<p>True enough. MySQLdb fakes it, though, because the spec requires it.
<sect1>cursor.rollback() is missing!
<p>MySQL doesn't do transactions. <tt/cursor.rollback()/ is supposed to
roll back (cancel) the current transaction. If you really need to do
this, then you definitely want <tt/cursor.rollback()/ to fail, because
it can't do what you want it to do.
<p>OTOH, <tt/cursor.commit()/, which attempts to commit the transaction
to the database, <em/does/ exist and always succeeds, because MySQL
essentially is always in auto-commit mode.
<p>MySQL-3.23 will, sometime in the near future, support transactions.
When this happens, <tt/cursor.commit()/ will actually do something
(and may fail if MySQL returns an error or warning condition), and
<tt/cursor.rollback()/ will actually exist and undo the current transaction.
<sect1>How do I use some of the special MySQL features?
<P>Short answer: Don't, if you can avoid it. Your program will not
be portable to other databases.
<P>Long answer: MySQLdb exports all symbols from _mysql. There are only
a couple MySQL functions available this way, though. The Connection object
does wrap nearly all of the various MySQL calls that use a <tt/MYSQL/
argument (the connection handle in the C API). So let's say you want to
use <tt/mysql_select_db(newdb)/. In MySQLdb, that's
<tt/db.select_db(newdb)/ where <tt/db/ is your Connection object.
<sect1>I still wanna use _mysql directly.
<p>Well, it <tt/may/ be appropriate in some cirumstances. The patched
ZMySQLDA does this, because MySQLdb does a lot of type conversion that
isn't necessary for Zope's purposes.
<enum>
<item>
Read the MySQL docs, particularly the C API, for an overview.
<item>
Read the MySQLdb docs. This shows how the C API is transliterated
into Python.
</enum>
</article>