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<h4 class="subsection">8.4.2 Changing the Schema</h4>
<p>To make a change to the database schema, follow these steps:
<ol type=1 start=1>
<li>
Increment <code>CURRENT_VERSION</code> in <code>buildbot/db/schema/manager.py</code> by
one. This is your new version number.
<li>
Create <samp><span class="file">buildbot/db/schema/vN.py</span></samp>, where N is your version number, by
copying the previous script and stripping it down. This script should define a
subclass of <code>buildbot.db.schema.base.Updater</code> named <code>Updater</code>.
<p>The class must define the method <code>upgrade</code>, which takes no arguments. It
should upgrade the database from the previous version to your version,
including incrementing the number in the <code>VERSION</code> table, probably with an
<code>UPDATE</code> query.
<p>Consult the API documentation for the base class for information on the
attributes that are available.
<li>
Edit <samp><span class="file">buildbot/test/unit/test_db_schema_master.py</span></samp>. If your upgrade
involves moving data from the basedir into the database proper, then edit
<code>fill_basedir</code> to add some test data.
<p>Add code to <code>assertDatabaseOKEmpty</code> to check that your upgrade works on an
empty database.
<p>Add code to <code>assertDatabaseOKFull</code> to check that your upgrade works on a
database with pre-existing data. Do this even if your changes do not move any
data from the basedir.
<p>Run the tests to find the bugs you introduced in step 2.
<li>
Increment the version number in the <code>test_get_current_version</code> test in the
same file. Only do this after you've finished the previous step - a failure of
this test is a good reminder that testing isn't done yet.
<li>
Updated the version number in <samp><span class="file">buildbot/db/schema/tables.sql</span></samp>, too.
<li>
Finally, make the corresponding changes to <samp><span class="file">buildbot/db/schema/tables.sql</span></samp>.
</ol>
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