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diff --git a/.html/dev/liquibase.html b/.html/dev/liquibase.html deleted file mode 100644 index 64b19c5..0000000 --- a/.html/dev/liquibase.html +++ /dev/null @@ -1,151 +0,0 @@ -<!DOCTYPE html> -<html> -<head> - <title> - The Codex » - Liquibase - </title> - - <link - rel='stylesheet' - type='text/css' - href='http://fonts.googleapis.com/css?family=Buenard:400,700&subset=latin,latin-ext'> - <link - rel="stylesheet" - type="text/css" - href="../media/css/reset.css"> - <link - rel="stylesheet" - type="text/css" - href="../media/css/grimoire.css"> -</head> -<body> - -<div id="shell"> - - <ol id="breadcrumbs"> - - <li class="crumb-0 not-last"> - - <a href="../">index</a> - - </li> - - <li class="crumb-1 not-last"> - - <a href="./">dev</a> - - </li> - - <li class="crumb-2 last"> - - liquibase - - </li> - - </ol> - - - - <div id="article"> - <h1 id="liquibase">Liquibase</h1> -<p>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.</p> -<hr> -<p>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 -<a href="http://wiki.rubyonrails.org/rails/pages/understandingmigrations">migration</a> -support, and <a href="http://code.google.com/p/django-evolution/">evolutions</a> or -<a href="http://south.aeracode.org">South</a> for Django, there are few tools that -actually track changes to the database or to the model in a reproducible way.</p> -<p>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 <abbr title="Data Definition Language">DDL</abbr> statements as a degenerate -form of diff, between two database states, that's not combinable the way -textual diff is except by concatenation.</p> -<p>Someone on IRC mentioned <a href="http://www.liquibase.org/">Liquibase</a> and -<a href="http://migrate4j.sourceforge.net/">migrate4j</a> 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.</p> -<p>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.</p> -<p>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.</p> -<p>The developers designed the configuraton file around some of the ideas from -<a href="http://www.amazon.com/Refactoring-Databases-Evolutionary-Addison-Wesley-Signature/dp/0321293533">Refactoring -Databases</a>, -and provided an <a href="http://www.liquibase.org/manual/home#available_database_refactorings">extensive list of canned -changes</a> -as primitives in the database change scripts. However, it's also possible to -insert raw SQL commands (either <abbr title="Data Definition Language">DDL</abbr>, or <abbr title="Data Manipulation Language">DML</abbr> queries like <code>SELECT</code>s and -<code>INSERT</code>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.</p> -<p>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.</p> -<p>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 <code>java</code> 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.</p> -<p>The liquibase developers deserve a lot of credit for solving a hard problem -very cleanly.</p> - </div> - - - -<div id="comments"> -<div id="disqus_thread"></div> -<script type="text/javascript"> - /* * * CONFIGURATION VARIABLES: EDIT BEFORE PASTING INTO YOUR WEBPAGE * * */ - var disqus_shortname = 'grimoire'; // required: replace example with your forum shortname - - /* * * DON'T EDIT BELOW THIS LINE * * */ - (function() { - var dsq = document.createElement('script'); dsq.type = 'text/javascript'; dsq.async = true; - dsq.src = 'http://' + disqus_shortname + '.disqus.com/embed.js'; - (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(dsq); - })(); -</script> -<noscript>Please enable JavaScript to view the <a href="http://disqus.com/?ref_noscript">comments powered by Disqus.</a></noscript> -<a href="http://disqus.com" class="dsq-brlink">comments powered by <span class="logo-disqus">Disqus</span></a> -</div> - - - - <div id="footer"> - <p> - - The Codex — - - Powered by <a href="http://markdoc.org/">Markdoc</a>. - -<a href="https://bitbucket.org/ojacobson/grimoire.ca/src/master/wiki/dev/liquibase.md">See this page on Bitbucket</a> (<a href="https://bitbucket.org/ojacobson/grimoire.ca/history-node/master/wiki/dev/liquibase.md">history</a>). - - </p> - </div> - -</div> -</body> -</html>
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