Multiple PreConditions

Question

I am implementing a changeset in Liquibase that needs a few different preconditions to be valid before it attempts to run.

Scenario #1: If table A,B,C exists, mark as ran

Scenario #2: If table X,Y,Z doesn't exist, halt execution of changeset

In other words, I need two <preConditions> tags with different onFail clauses. Is this at all allowed in Liquibase? I can't seem to make it work. The docs aren't very informative.

Answer 1

It is not allowed currently. There can be just one block.

Would it work to break it up into two separate changeSets?

Answer 2

A workaround that I've simply used:

• create a normal precondition

  <!-- pre-condition tests -->
  <preConditions onFail="WARN">
          <runningAs username="${db.maintenance.user}" />
  </preConditions>
  

• create an empty changeSet for another onFail level

  <changeSet id="liquibase-pre-1" author="liquibase" runAlways="true" runOnChange="true" runInTransaction="false">
      <preConditions onFail="HALT" onFailMessage="...">
          <!-- ... -->
      </preConditions>
      <sql>
          select 1 <!-- (Postgresql) or "select 1 from dual" (Oracle) -->
      </sql>
  </changeSet>
  

Answer 3

Combine them with <or> or <and> like this:

<preConditions>
    <or>
        <runningAs username="liquibase" />
        <runningAs username="sa" />
    </or>
</preConditions>

Here is some documentation on preConditions.