Jakob Külzer Ninja Coding Monkey goes Canada

Liquibase Incremental DB Diff

After discussing this on the Groovy and Grails Exchange, I finally put together a new version of the db diff script that I've mentioned in an earlier post. I couldn't find the original version that I've written a couple of months ago, so I hacked together a new one. It's far from perfect, efficient or beautiful, but it does what it is supposed to.

So, what's the idea behind this script? Everybody that uses Liquibase (if you are not, check out my blog post about what Liquibase is and how to use it) knows how painful it is to update your changelog.xml. Liquibase already gives you a great tool to start with, the db-diff command. However, it is hardcoded to diff the current environment's database against the test database. This is annoying as you'll have to modify your datasources and keep the database schema updated manually. But fear not, here is my (surprisingly) easy solution.

I've created a simple script (or rather, I took the db-diff script and hacked it), which I've called incremental DB diff (all the other cool names are already taken...) and what it does is the following:

1. update the schema in the db-diff (or whatever you call it) database using the changelog.xml
2. diff the database of the current environment against this database and output the diff as Liquibase XML

So, how is this a good thing? Easy: this little script will automatically create a target database to diff against using the changelog.xml which is good, as the changelog.xml represents your last migration status. And as it uses a separate database it doesn't influence the test database.

After running the script just put the output in the changelog.xml and you're done.

All you have to do to use this is to drop the file into your /scripts/ directory, create a new database and an according datasource entry for the environment "dbdiff" like this:

	dbdiff {
		dataSource {
			driverClassName = "com.mysql.jdbc.Driver"
			dbCreate = "create-drop"
			url = "jdbc:mysql://localhost/foo_dbdiff"
			username = "foo"
			password = "bar"
		}
	}

Download DbDiffIncremental.groovy. Drop me a mail or a comment if you have questions.