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-# Liquibase
-
-Note to self: I think this (a) needs an outline and (b) wants to become a “how
-to automate db upgrades for dummies” page. Also, this is really old (~2008)
-and many things have changed: database migration tools are more
-widely-available and mature now. On the other hand, I still see a lot of
-questions on IRC that are based on not even knowing these tools exist.
-
------
-
-Successful software projects are characterized by extensive automation and
-supporting tools. For source code, we have version control tools that support
-tracking and reviewing changes, marking particular states for release, and
-automating builds. For databases, the situation is rather less advanced in a
-lot of places: outside of Rails, which has some rather nice
-[migration](http://wiki.rubyonrails.org/rails/pages/understandingmigrations)
-support, and [evolutions](http://code.google.com/p/django-evolution/) or
-[South](http://south.aeracode.org) for Django, there are few tools that
-actually track changes to the database or to the model in a reproducible way.
-
-While I was exploring the problem by writing some scripts for my own projects,
-I came to a few conclusions. You need to keep a receipt for the changes a
-database has been exposed to in the database itself so that the database can
-be reproduced later. You only need scripts to go forward from older versions
-to newer versions. Finally, you need to view DDL statements as a degenerate
-form of diff, between two database states, that's not combinable the way
-textual diff is except by concatenation.
-
-Someone on IRC mentioned [Liquibase](http://www.liquibase.org/) and
-[migrate4j](http://migrate4j.sourceforge.net/) to me. Since I was already in
-the middle of writing a second version of my own scripts to handle the issues
-I found writing the first version, I stopped and compared notes.
-
-Liquibase is essentially the tool I was trying to write, only with two years
-of relatively talented developer time poured into it rather than six weeks.
-
-Liquibase operates off of a version table it maintains in the database itself,
-which tracks what changes have been applied to the database, and off of a
-configuration file listing all of the database changes. Applying new changes
-to a database is straightforward: by default, it goes through the file and
-applies all the changes that are in the file that are not already in the
-database, in order. This ensures that incremental changes during development
-are reproduced in exactly the same way during deployment, something lots of
-model-to-database migration tools have a problem with.
-
-The developers designed the configuraton file around some of the ideas from
-[Refactoring
-Databases](http://www.amazon.com/Refactoring-Databases-Evolutionary-Addison-Wesley-Signature/dp/0321293533),
-and provided an [extensive list of canned
-changes](http://www.liquibase.org/manual/home#available_database_refactorings)
-as primitives in the database change scripts. However, it's also possible to
-insert raw SQL commands (either DDL, or DML queries like `SELECT`s and
-`INSERT`s) at any point in the change sequence if some change to the database
-can't be accomplished with its set of refactorings. For truly hairy databases,
-you can use either a Java class implementing your change logic or a shell
-script alongside the configuration file.
-
-The tools for applying database changes to databases are similarly flexible:
-out of the box, liquibase can be embedded in a fairly wide range of Java
-applications using servlet context listeners, a Spring adapter, or a Grails
-adapter; it can also be run from an ant or maven build, or as a standalone
-tool.
-
-My biggest complaint is that liquibase is heavily Java-centric; while the
-developers are planning .Net support, it'd be nice to use it for Python apps
-as well. Triggering liquibase upgrades from anything other than a Java program
-involves either shelling out to the `java` command or creating a JVM and
-writing native glue to control the upgrade process, which are both pretty
-painful. I'm also less than impressed with the javadoc documentation; while
-the manual is excellent, the javadocs are fairly incomplete, making it hard to
-write customized integrations.
-
-The liquibase developers deserve a lot of credit for solving a hard problem
-very cleanly.
-
-*[DDL]: Data Definition Language
-*[DML]: Data Manipulation Language