[Py-howto-checkins] CVS: pyhowto/zodb Makefile,NONE,1.1 chatter.py,NONE,1.1 gfdl.tex,NONE,1.1 introduction.tex,NONE,1.1 modules.tex,NONE,1.1 prog-zodb.tex,NONE,1.1 storages.tex,NONE,1.1 transactions.tex,NONE,1.1 zeo.tex,NONE,1.1 zodb.tex,NONE,1.1

[A.M. K. <aku...@us...>]

Update of /cvsroot/py-howto/pyhowto/zodb
In directory slayer.i.sourceforge.net:/tmp/cvs-serv10693

Added Files:
	Makefile chatter.py gfdl.tex introduction.tex modules.tex 
	prog-zodb.tex storages.tex transactions.tex zeo.tex zodb.tex 
Log Message:
Initial checkin


--- NEW FILE ---

TEX_FILES = gfdl.tex introduction.tex  modules.tex  prog-zodb.tex  \
            storages.tex  transactions.tex  zeo.tex  zodb.tex 

MKHOWTO=../../tools/mkhowto

zodb.dvi:  
	$(MKHOWTO) --dvi zodb.tex

--- NEW FILE ---

import sys, time, os, random

from ZEO import ClientStorage
import ZODB
from ZODB.POSException import ConflictError
from Persistence import Persistent
import BTree

class ChatSession(Persistent):

    """Class for a chat session.
    Messages are stored in a B-tree, indexed by the time the message
    was created.  (Eventually we'd want to throw messages out,

    add_message(message) -- add a message to the channel
    new_messages()       -- return new messages since the last call to
                            this method
    
    
    """

    def __init__(self, name):
        """Initialize new chat session.
        name -- the channel's name
        """

        self.name = name

        # Internal attribute: _messages holds all the chat messages.
        
        self._messages = BTree.BTree()
        

    def new_messages(self):
        "Return new messages."

        # self._v_last_time is the time of the most recent message
        # returned to the user of this class. 
        if not hasattr(self, '_v_last_time'):
            self._v_last_time = 0

        new = []
        T = self._v_last_time

        for T2, message in self._messages.items():
            if T2 > T:
                new.append( message )
                self._v_last_time = T2

        return new
    
    def add_message(self, message):
        """Add a message to the channel.
        message -- text of the message to be added
        """

        while 1:
            try:
                now = time.time()
                self._messages[ now ] = message
                get_transaction().commit()
            except ConflictError:
                # Conflict occurred; this process should pause and
                # wait for a little bit, then try again.
                time.sleep(.2)
                pass
            else:
                # No ConflictError exception raised, so break
                # out of the enclosing while loop.
                break
        # end while

def get_chat_session(conn, channelname):
    """Return the chat session for a given channel, creating the session
    if required."""

    # We'll keep a B-tree of sessions, mapping channel names to
    # session objects.  The B-tree is stored at the ZODB's root under
    # the key 'chat_sessions'.
    root = conn.root()
    if not root.has_key('chat_sessions'):
        print 'Creating chat_sessions B-tree'
        root['chat_sessions'] = BTree.BTree()
        get_transaction().commit()
        
    sessions = root['chat_sessions']

    # Get a session object corresponding to the channel name, creating
    # it if necessary.
    if not sessions.has_key( channelname ):
        print 'Creating new session:', channelname
        sessions[ channelname ] = ChatSession(channelname)
        get_transaction().commit()

    session = sessions[ channelname ]
    return session
    

if __name__ == '__main__':
    if len(sys.argv) != 2:
        print 'Usage: %s <channelname>' % sys.argv[0]
        sys.exit(0)

    storage = ClientStorage.ClientStorage( ('localhost', 9672) )
    db = ZODB.DB( storage )
    conn = db.open()

    s = session = get_chat_session(conn, sys.argv[1])

    messages = ['Hi.', 'Hello', 'Me too', "I'M 3L33T!!!!"]

    while 1:
        # Send a random message
        msg = random.choice(messages)
        session.add_message( '%s: pid %i' % (msg,os.getpid() ))

        # Display new messages
        for msg in session.new_messages():
            print msg

        # Wait for a few seconds
        pause = random.randint( 1, 4 ) 
        time.sleep( pause )
        

--- NEW FILE ---
% fdl.tex 
% This file is a chapter.  It must be included in a larger document to work
% properly.

\section{GNU Free Documentation License}

Version 1.1, March 2000\\

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--- NEW FILE ---

%Introduction
%   What is ZODB?
%   What is ZEO?
%           How ZEO works (ClientStorage)
%   OODBs vs. Relational DBs
%   Other OODBs

\section{Introduction}

This HOWTO explains how to write Python programs that use the Z Object
Database (ZODB) and Zope Enterprise Objects (ZEO).

\subsection{What is ZODB?}

The ZODB is a persistence system for Python objects.  Persistent
programming languages provide facilities that automatically write
objects to disk and read them in again when they're required by a
running program.  

It's certainly possible to build your own system for making Python
objects persistent.  The usual starting points are the \module{pickle}
module, for converting objects into a string representation, and
database modules, such as the \module{gdbm} or \module{bsddb} modules,
provide ways to write strings to disk and read them back.  It's
straightforward to combine the \module{pickle} module and a database
module to store and retrieve objects, and in fact the \module{shelve}
module, included in Python's standard library, does this.  

The downside is that the programmer has to explicitly manage objects,
reading an object when it's needed and writing it out to disk when the
object is no longer required.  The ZODB manages objects for you,
keeping them in a cache and writing them out if they haven't been 
accessed in a while.  



\subsection{OODBs vs. Relational DBs}

Another way to look at it is that the ZODB is a Python-specific
object-oriented database (OODB).  

Relational databases (RDBs) are far more common than OODBs.
Relational databases store information in tables; a table consists of 
any number of rows, each row containing several columns of
information.  

Let's introduce the example that we'll be using through this document.
The example comes from my day job working for the MEMS Exchange, in a
greatly simplified version.  

XXX explain a bit more

The job is to track process runs, which are lists of manufacturing  steps
to be performed in a semiconductor fab.  A run is owned by a
particular user, and has a name and assigned ID number.  Runs consist
of a number of operations; an operation is a single step to be
performed, such as depositing something on a wafer or etching
something off it.  Operations may have parameters, which are
additional information required to perform an operation.  For example,
if you're depositing something on a wafer, you need to know two
things: 1) what you're depositing, and 2) how much should be
deposited.
You might deposit 100 microns of silicon oxide, or 1 micron of copper.

Mapping these structures to a relational database is straightforward:

runs
run_id   owner   title   acct_num

operations
run_id step_id  process_id 

parameters 
run_id step_id param_name param_value


In an object-oriented programming language, you would write three
classes:

class Run:
    .run_id
... XXX finish

If you were

\subsection{What is ZEO?}

\subsection{About the Author}
\label{intro:author}


--- NEW FILE ---

% Related Modules
%    PersistentMapping
%    PersistentList
%    BTree
%    Catalog

\section{Related Modules}
\subsection{PersistentMapping}

\subsection{PersistentList}
\subsection{BTree}
\subsection{Catalog}


--- NEW FILE ---

%ZODB Programming
%   How ZODB works (ExtensionClass, dirty bits)
%   Installing ZODB
%   Rules for Writing Persistent Classes
   

\section{ZODB Programming}

\subsection{How ZODB Works}

XXX (ExtensionClass, dirty bits)


\subsection{Installing ZODB}

The ZODB forms part of Zope, but it's difficult and somewhat painful
to disentangle the bits from Zope that you need to write Python
programs that use only the ZODB.  Accordingly I've gone ahead and
packaged only the packages required for the ZODB, so you can install
them and start programming.

These packages are quite young and are still experimental; don't be
surprised if the installation process runs into problems.  Please
inform me of any difficulties you encounter.

\subsubsection{Requirements}

You'll need Python, of course; version 1.5.2 certainly works, and the
ZODB code seems to compile using the Python 2.0 CVS tree.

The code is packaged using the new distribution tools, so first you'll
have to get the latest Distutils release from the Distutils SIG page
at \url{http://www.python.org/sigs/distutils-sig/download.html}, and
install it.  This is simply a matter of untarring or unzipping the
release package, and then running \code{python setup.py install}.

Be sure you have the
latest version of Distutils; if you encounter problems compiling
ZODB/TimeStamp.c or your compiler reports an error like "Can't create
build/temp.linux2/ExtensionClass.o: No such file or directory", you
need an updated version.  Old versions of Distutils have two bugs
which affect the setup scripts.  First, for a long time the
define_macros keyword in setup.py files didn't work due to a Distutils
bug, so I hacked TimeStamp.c in earlier releases.  The Distutils have
since been fixed, and the hack became unnecessary, so I removed it.
Second, the code that creates directories tries to be smart and caches
them to save time by not trying to create a directory twice, but this
code was broken in old versions of Distutils.

\subsubsection{Installing the Packages}

Download the ZODB
tarball containing all the packages for both ZODB and ZEO from
\url{http://www.kuchling.com/files/zodb/}.  

Run the standard command for installing software using the
Distutils: \code{python setup.py install}.  If you encounter any
problems, please let me know.


\subsection{Rules for Writing Persistent Classes}



--- NEW FILE ---

% Storages
%    FileStorage
%    BerkeleyStorage
%    OracleStorage

\section{Storages}
\subsection{   FileStorage}
\subsection{   BerkeleyStorage}
\subsection{   OracleStorage}

--- NEW FILE ---
%Transactions and Versioning
%   Committing and Aborting
%   Subtransactions
%   Versions
%   Multithreaded ZODB Programs
   

\section{Transactions and Versioning}

\subsection{Committing and Aborting}
\subsection{Subtransactions}
\subsection{Versions}
\subsection{Multithreaded ZODB Programs}

   

--- NEW FILE ---

% ZEO
%    How ZEO works (ClientStorage)
%    Installing ZEO
%    Configuring ZEO
   
\section{ZEO}
\subsection{How ZEO Works}
XXX (ClientStorage)
   
\subsection{Installing ZEO}


This package contains the Python code for ZEO, packaged to make it
easier to set up and run a ZEO Storage Server on your machine.  Most
notably, I've rewritten the \code{start.py} script to use a
configuration file and renamed it to \code{zeod}.

WARNING: This packaging is HIGHLY EXPERIMENTAL and has only been
tested on one machine, which happened to be running Red Hat 6.2.  I
fully expect there to be problems and incompatibilities on other Unix
variants or even other Linux distributions.  Please inform me of any
problems, or post your questions to the ZEO mailing list at
\email{zop...@zo...}.

\subsubsection{Requirements}

To run a ZEO server, you'll need Python 1.5.2 or 2.0, and the ZODB
packages from \url{http://www.kuchling.com/files/zodb/}
have to be installed.  

\emph{Note for Python 1.5.2 users}: ZEO requires updated versions
of the \code{asyncore.py} and \code{asynchat.py} modules
that are included in 1.5.2's standard library.  You can grab copies of
the Python 2.0 versions of these modules from the above Web site, or from
the Python 2.0 distribution.

\subsubsection{Installation}

The \code{setup.py} script won't do all the work for you at
the moment, since two scripts need to go into odd locations and the
Distutils don't seem to support this at the moment.  One script goes
into \code{/etc/rc.d/init.d}, so you can configure your system
to start a ZEO Storage Server at boot-up.  

\begin{enumerate}

\item  Run \code{python setup.py install} to install the ZEO/
package into your Python installation.

\item  Copy various files into their proper locations:
\begin{verbatim}
cp zeo.conf /usr/local/etc/ ; chmod 644 /usr/local/etc/zeo.conf
cp zeo /etc/rc.d/init.d ; chmod 755 /etc/rc.d/init.d/zeo
cp zeod /usr/local/bin ; chmod 755 /usr/local/bin/zeod
\end{verbatim}

\item  Edit \code{/usr/local/etc/zeo.conf} 
appropriately for your desired setup.

\end{enumerate}

To test whether ZEO is working correctly, try running the following
lines of code, which will connect to the server, add some bits of data
to the root of the ZODB, and commits the transaction:

\begin{verbatim}
from ZEO import ClientStorage
from ZODB import DB

# Change next line to connect to your ZEO server
storage = ClientStorage.ClientStorage( ('kronos', 1972) )
db = DB( storage )
conn = db.open()
root = conn.root()

# Store some things in the root
root['list'] = ['a', 'b', 1.0, 3]
root['dict'] = {'a':1, 'b':4}

# Commit the transaction
get_transaction().commit()
\end{verbatim}

If this code runs properly, then your ZEO server is probably working
correctly.

\subsection{Configuring ZEO}
   

--- NEW FILE ---
\documentclass{howto}

\title{ZODB/ZEO HOWTO}
\release{0.01}

\author{A.M.\ Kuchling}
\authoraddress{am...@bi...}

\begin{document}
\maketitle
\tableofcontents

\copyright{Copyright $\copyright$  2000 A.M. Kuchling.
      Permission is granted to copy, distribute and/or modify this document
      under the terms of the GNU Free Documentation License, Version 1.1
      or any later version published by the Free Software Foundation;
      with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
      A copy of the license is included in the appendix entitled ``GNU
      Free Documentation License''.}

\input{introduction}
\input{prog-zodb}
\input{transactions}
\input{modules}
\input{storages}
\input{zeo}

\appendix
\input gfdl.tex

\end{document}