Update existing ZODB databases to match your software
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README.rst

zodbupdate - Update existing databases to match your software

This package provides a tool that automatically identifies and updates references from persistent objects to classes that are in the process of being moved from one module to another and/or being renamed.

If a class is being moved or renamed, you need to update all references from your database to the new name before finally deleting the old code.

This tool looks through all current objects of your database, identifies moved/renamed classes and touches objects accordingly. It creates transactions that contains the update of your database (one transaction every 100000 records).

Having run this tool, you are then free to delete the old code.

Usage

Installing the egg of this tool provides a console script zodbupdate which you can call giving either a FileStorage filename or a configuration file defining a storage:

$ zodbupdate -f Data.fs
$ zodbupdate -c zodb.conf

Detailed usage information is available:

$ zodbupdate -h

Custom software/eggs

It is important to install this egg in an interpreter/environment where your software is installed as well. If you're using a regular Python installation or virtualenv, just installing the package using easy_install should be fine.

If you are using buildout, installing can be done using the egg recipe with this configuration:

[buildout]
parts += zodbupdate

[zodbupdate]
recipe = zc.recipe.egg
eggs = zodbupdate
    <list additional eggs here>

If you do not install zodbupdate together with the necessary software it will report missing classes and not touch your database.

Non-FileStorage configurations

You can configure any storage known to your ZODB installation by providing a ZConfig configuration file (similar to zope.conf). For example you can connect to a ZEO server by providing a config file zeo.conf:

<zeoclient>
    server 127.0.0.1:8100
    storage 1
</zeoclient>

And then running zodbupdate using:

$ zodbupdate -c zeo.conf

Pre-defined rename rules

Rename rules can be defined using an entry point called zodbupdate:

setup(...
      entry_points = """
      [zodbupdate]
      renames = mypackage.mymodule:rename_dict
      """)

Those entry points must points to dictionaries that map old class names to new class names:

rename_dict = {
    'mypackage.mymodule ClassName':
    'otherpackage.othermodule OtherClass'}

As soon as you have rules defined, you can already remove the old import location mentioned in them.

Packing

The option --pack will pack the storage on success. (You tell your users to use that option. If they never pack their storage, it is a good occasion).

Migration to Python 3

zodbupdate can be used to migrate a database created with a Python 2 application to be usable with the same application in Python 3. To accomplish this, you need to:

  1. Stop your application. Nothing should be written to the database while the migration is running.
  2. Update your Python 2 application to use the latest ZODB version. It will not work with ZODB 3.
  3. With Python 2, run zodbupdate --pack --convert-py3.

If you use a Data.fs we recommend you to use the -f option to specify your database. After the conversion the magic header of the database will be updated so that you will be able to open the database with Python 3.

If you use a different storage (like RelStorage), be sure you will be connecting to it using your Python 3 application after the migration. You will still be able to connect to your database and use your application with Python 2 without errors, but then you will need to convert it again to Python 3.

While the pack is not required, it is highly recommended.

The conversion will take care of the following tasks:

  • Updating stored Python datetime, date and time objects to use Python 3 bytes,
  • Updating ZODB references to use Python 3 bytes.
  • Optionally convert stored strings to either unicode or bytes pending your configuration.

If your application expect to use bytes in Python 3, they must be stored as such in the database, and all other strings must be stored as unicode string, if they contain other characters than ascii characters.

When using --convert-py3, zodbupdate will load a set of decoders from the entry points:

setup(...
      entry_points = """
      [zodbupdate.decode]
      decodes = mypackage.mymodule:decode_dict
      """)

Decoders are dictionaries that specifies as keys attributes on Persistent classes that must either be encode as bytes (if the value is binary) or decoded to unicode using value as encoding (for instance utf-8 here):

decode_dict = {
   'mypackage.mymodule ClassName attribute': 'binary',
   'otherpackage.othermodule OtherClass other_attribute': 'utf-8'}

Please note that for the moment only attributes on Persistent classes are supported.

Problems and solutions

Your Data.fs has POSKey errors

If you call zodbupdate with -f and the path to your Data.fs, records triggering those errors will be ignored.

You have an another error

We recommand to run zodbupdate with -v -d to get the maximum of information.

If you are working on big storages, you can use the option -o to re-run zodbupdate at a failing record you previously encountered afterward.