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POSpring Batch: migrating 1 to n relationship where n is potentially huge
 

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    <p>I am experienced with Spring, but new to Spring Batch. Now I have the task to migrate a data structure from a simple structure in one database to a complexer one in the other. The data structure corresponds to an object hierarchy that I will name like this </p> <pre><code>OldParent 1 --&gt; n OldChild // old system NewParent 1 --&gt; n NewChild // new system </code></pre> <p>In the old db, there are only two tables, in the new system, things get a lot more complex and there are 8 tables, but that is irrelevant for now.</p> <p>Basically I would like to use a simple JDBC-based solution with rowmappers reading from OldParent and converting to NewParent.</p> <p>So here would be a basic configuration snippet:</p> <pre><code>&lt;batch:job id="migration"&gt; &lt;batch:step id="convertLegacyData"&gt; &lt;batch:tasklet&gt; &lt;batch:chunk reader="parentReader" writer="parentWriter" commit-interval="200" /&gt; &lt;/batch:tasklet&gt; &lt;/batch:step&gt; &lt;/batch:job&gt; </code></pre> <p>In this scenario, the parentReader would acquire and convert the OldChild objects, probably delegating to a childReader / childWriter objects.</p> <p>The problem is this: while there are several hundred thousand Parents, each Parent can have zero to several million children, so the commit-interval based on parent would not help at all, but I would very much like to have a configurable commit interval.</p> <p>So another solution would be to make the workflow child-based:</p> <pre><code>&lt;batch:job id="migration"&gt; &lt;batch:step id="convertLegacyData"&gt; &lt;batch:tasklet&gt; &lt;batch:chunk reader="childReader" writer="childWriter" commit-interval="200" /&gt; &lt;/batch:tasklet&gt; &lt;/batch:step&gt; &lt;/batch:job&gt; </code></pre> <p>In this scenario, the childReader would have to also read OldParent objects and write NewParents, delegating to parentReader and parentWriter objects. The major drawback here is that I am losing all OldParents that don't have associated OldChild objects.</p> <p>The third possible scenario would be to have two different workflows for <code>OldParent -&gt; NewParent</code> and <code>OldChild -&gt; NewChild</code>. (I would have to maintain a mapping table that stores the relationship between OldParent and NewParent ids, but I could use standard configurations including commit-interval.</p> <p>Are there other possibilities? Which of these would you recommend as best practice?</p>
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