A new topic, 'Looking for Feedback: Change implementations and Extensions', has
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You can see it at
http://liquibase.org/forum/index.php?topic=104.new#new
The text of the topic is shown below:
I am thinking about how we select the Change implementation to run from your
changelog files when you have liquibase extensions installed. Currently, if
you have something like this:
Code:
<databaseChangeLog
xmlns="http://www.liquibase.org/xml/ns/dbchangelog";
xmlns:ext="http://www.liquibase.org/xml/ns/dbchangelog-ext";
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-2.0.xsd
http://www.liquibase.org/xml/ns/dbchangelog-ext
http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-ext.xsd";>
<changeSet id="1" author="nvoxland">
<createTable tableName="asdf">
<column name="id" type="int"/>
</createTable>
</changeSet>
<changeSet id="2" author="nvoxland">
<ext:sample2/>
</changeSet>
</databaseChangeLog>
LiquiBase will find the "createTable" change provided by liquibase, and will
look for a "sample2" change in the classpath as well.
But what if you want to modify the behavior of createTable? Currently, if you
create an extension with a "createTable" change liquibase will use the one that
returns the one where the getPriority() method returns the highest value. The
idea is that this setup will allow you to drop in change extensions that modify
the behavior of your changelog without needing to modify the changelog at all.
The example I had in my head was a drop-in replacement for <insert> which will
call "set identity insert on/off" before/after inserting for sqlserver.
Any opinions on if that is a good approach? The other option that I have been
thinking about is something more like what you see for custom components in
Flex or WPF where you include the package name in as the namespace for tags.
That way you need to change your changelog if you want a different
implementation of a core change tag, but you also know exactly what is going to
run. It is also too xml-ish for me, as I want to better support non-xml
changelog definitions, though how you would work around the issue would need to
be determined by the creators of alternate formats.
Nathan
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