Kotlin Liquibase

A pluggable parser for Liquibase that allows the creation of changelogs in a Kotlin DSL, rather than hurtful XML. If this DSL isn't reason enough to adopt Liquibase, then there is no hope for you. This project is HEAVILY based off of Groovy Liquibase which was started by Tim Berglund, and is currently maintained by Steve Saliman.

News

Additions to the XML format:

• In general, boolean attributes can be specified as either strings or booleans. For example, changeSet(runAlways = "true") can also be written as changeSet(runAlways = true).
• The Kotlin DSL supports a simplified means of passing arguments to the executeCommand change. Instead of:

execute {
  arg(value = "somevalue")
}

You can use this the simpler form:

execute {
  arg("somevalue")
}

• The sql change does not require a closure for the actual SQL. You can just pass the string like this: sql("select some_stuff from some_table") If you want to use the comments element of a sql change, you need to use the closure form, and the comment must be in the closure BEFORE the SQL, like this:

sql {
  comment("we should not have added this...")
  -"delete from my_table"
}

• The stop change can take a message as an argument as well as an attribute. In other words, stop("message") works as well as the more XMLish stop(message = "message")
• A customPrecondition can take parameters. the XMLish way to pass them is with param(name = "myParam", value = "myValue") statements in the customPrecondition"s closure. In the Kotlin DSL, you can also have myParam("myValue")
• The validChecksum element of a change set is not well documented. Basically you can use this when changeSet's current checksum will not match what is stored in the database. This might happen if you, for example want to reformat a changeSet to add white space. This doesn't change the functionality of the changeset, but it will cause Liquibase to generate new checksums for it. The validateChecksum element tells Liquibase to consider the checksums in the validChecksum element to be valid, even if it doesn't match what is in the database.
• The Liquibase documentation tells you how to set a property for a databaseChangeLog by using the property element. What it doesn't tell you is that you can also set properties by loading a property file. To do this, you can have property(file = "my_file.properties") in the closure for the databaseChangeLog.
• Liquibase has an includeAll element in the databaseChangeLog that includes all the files in the given directory. The Kotlin DSL implementation only includes kotlin files, and it makes sure they are included in alphabetical order. This is really handy for keeping changes in a different file for each release. As long as the file names are named with the release numbers in mind, Liquibase will apply changes in the correct order.
• Remember, the Kotlin DSL is basically just Kotlin closures, so you can use kotlin code to do things you could never do in XML, such as this:

sql { """
  insert into some_table(data_column, date_inserted)
  values("some_data", "${Date().toString()}")
"""
}

Items that were left out of the XML documentation

• The createIndex and dropIndex changes have an undocumented associatedWith attribute. From an old Liquibase forum, it appears to be an attempt to solve the problem that occurs because some databases automatically create indexes on primary keys and foreign keys, and others don't. The idea is that you would have a change to create the primary key or foreign key, and another to create the index for it. The index change would use the associatedWith attribute to let Liquibase know that this index will already exist for some databases so that Liquibase can skip the change if we are in one of those databases. The Liquibase authors do say it is experimental, so use at your own risk...
• The executeCommand change has an undocumented os attribute. The os attribute is a string with a list of operating systems under which the command should execute. If present, the os.name system property will be checked against this list, and the command will only run if the operating system is in the list.
• The column element has some undocumented attributes that are pretty significant. They include:

  • valueSequenceNext, valueSequenceCurrent, and defaultValueSequenceNext, which appear to link values for a column to database sequences.

  • A column can be set auto-number if it the autoIncrement attribute is set to true, but did you know that you can also control the starting number and the increment interval with the startWith and incrementBy attributes?

• The constraints element also has some hidden gems:
  • Some databases automatically create indexes for primary keys. The primaryKeyTablespace can be used to control the tablespace.
  • There is also a checkConstraint attribute, that appears to be useful for defining a check constraint, but I could not determine the proper syntax for it yet. For now, it may be best to stick to custom sql changes to define check constraints.
• The createSequence change has an cacheSize attribute that sets how many numbers of the sequence will be fetched into memory for each query that accesses the sequence.
• The documentation for version 3.1.1 of Liquibase mentions the new beforeColumn, afterColumn, and position attributes that you can put on a column statement to control where a new column is placed in an existing table. What 1.2the documentation leaves out is that these attributes don't work :-)
• Version 3.4.0 of Liquibase introduced two new attributes to the includeAll element of a databaseChangeLog, both of which are undocumented. The first one is the errorIfMissingOrEmpty attribute. It defaults to true, but if it is set to false, Liquibase will ignore errors caused by invalid or empty directories and move on. The second one is the resourceFilter attribute. A resourceFilter is the name of a class that implements liquibase.changelog.IncludeAllFilter interface, which allows developers to implement sophisticated logic to decide what files from a directory should be included (in addition to the *.kts filter that the Kotlin DSL imposes).
• Liquibase 3.4.0 added the undocumented forIndexCatalogName, forIndexSchemaName, and forIndexName attributes to the addPrimaryKey and addUniqueConstraint changes. These attributes allow you to specify the index that will be used to implement the primary key and unique constraint, respectively.
• Liquibase 3.4.0 added the undocumented cacheSize and willCycle attributes to the alterSequence change. cacheSize sets how many numbers of the sequence will be fetched into memory for each query that accesses the sequence. willCycle determines if the sequence should start over when it reaches its maximum value.

License

This code is released under the Apache Public License 2.0, just like Liquibase 2.0.