<ul data-eligibleForWebStory="false"><li>Adding additional Count() in a Django ORM queryset can lead to performance issues due to Cartesian Product trap.</li><li>The problem arises when multiple Count() operations with distinct=True are used, leading to unnecessary JOINs and duplicated data.</li><li>The solution involves using subqueries to avoid the Cartesian Product trap and improve query performance significantly.</li><li>Lessons learned include testing aggregate queries with production data and being cautious with multi-branch JOINs to optimize performance.</li></ul>

The Cartesian Product Trap in Django ORM

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