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– Error upgrading database with Alembic </title>
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<h3><a href="http://thierry.ducrest.net/error-upgrading-database-with-alembic.html">Error upgrading database with Alembic</a></h3>
<span class="date-article">12 November 2016</span>
<div class="article_text">
<p>On my last project I started using <a href="https://bitbucket.org/zzzeek/alembic/overview">Alembic</a> as a migration tool for the database, which is a new thing for me.<br>
Before that I used to simply keep a file with the modifications applied to the developement database between each release version and patch the test and production datbase accordingly. Some of the drawbacks to this method are a risk of manipulation error and it is very difficult to reverse the changes when they are applied.</p>
<p>Today while performing an upgrade on the production database running Postgresql with Alembic :</p>
<div class="highlight"><pre><span></span>alembic upgrade head
</pre></div>
<p>I received the following error :</p>
<div class="highlight"><pre><span></span>...
ERROR <span class="o">[</span>alembic.util.messaging<span class="o">]</span> Online migration expected to match one row
when updating <span class="s1">'7b4f4b275d5b'</span> to <span class="s1">'cca4e32787e4'</span> in <span class="s1">'alembic_version'</span><span class="p">;</span> <span class="m">2</span> found
...
</pre></div>
<p>Each database that Alembic work with has an "alembic_version" table, with one column, which contains the id of the current version of the database.</p>
<p>In my database there was two rows in the table alembic_version both with the same value. As the table has no other column to differentiate the rows it is a little bit tricky to remove only one but this did the trick :</p>
<div class="highlight"><pre><span></span><span class="k">DELETE</span> <span class="k">FROM</span> <span class="n">alembic_version</span>
<span class="k">WHERE</span> <span class="n">ctid</span> <span class="k">IN</span> <span class="p">(</span><span class="k">select</span> <span class="n">ctid</span> <span class="k">from</span> <span class="n">alembic_version</span> <span class="k">LIMIT</span> <span class="mi">1</span><span class="p">);</span>
</pre></div>
<p>I do not know why there was two entries in the table but removing one fixed the problem.</p>
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<p>Posted on: Sat 12 November 2016</p>
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