Django DB-Side Computation

Use this skill when Django fetches rows into Python to compute values the database can compute more efficiently or more consistently.

Workflow

1. Identify the Python computation.

   • Counts, sums, min/max, booleans, latest related rows, rankings, denormalized totals, or per-row derived fields.
   • Confirm whether the computed value must be exact, current, and transactionally consistent.

2. Pick the SQL expression level.

   • filter(), exclude(), and F() for simple comparisons and updates.
   • annotate() and aggregates for per-object counts and totals.
   • Filtered aggregates for conditional counts and sums.
   • Exists() for yes/no related-row checks.
   • Subquery() with OuterRef() for latest or scalar related values.
   • Window() for ranks and running calculations.
   • GeneratedField for deterministic same-row computed columns when the database supports it.