store: Fix: Pydantic bare default evaluated at class definition time (paper-dynasty-database)

graph/fixes/fix-pydantic-bare-default-evaluated-at-class-definition-time-530bfb.md

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+---
+id: 530bfb6f-841c-4381-b8a4-d0b6fbc02878
+type: fix
+title: "Fix: Pydantic bare default evaluated at class definition time (paper-dynasty-database)"
+tags: [paper-dynasty, python, pydantic, fix, bug, fastapi]
+importance: 0.65
+confidence: 0.8
+created: "2026-03-03T20:06:06.122074+00:00"
+updated: "2026-03-03T20:06:06.122074+00:00"
+---
+
+## Problem
+
+`PlayerModel.offense_col` in `app/routers_v2/mlbplayers.py` used a bare `random.randint(1, 3)` as the Pydantic field default. Python evaluates this expression once at class definition time (module import), so every instance shared the same random integer for the entire process lifetime.
+
+## Root Cause
+
+Pydantic field defaults that are not wrapped in `Field(default_factory=...)` are evaluated eagerly at class body execution time — identical to how Python function default argument values work. This is a common footgun with mutable or randomised defaults.
+
+## Solution
+
+```python
+# Before (broken)
+offense_col: int = random.randint(1, 3)
+
+# After (correct)
+offense_col: int = pydantic.Field(default_factory=lambda: random.randint(1, 3))
+```
+
+`default_factory` is called on each model instantiation, producing a fresh value per request.
+
+## Files Changed
+
+- `app/routers_v2/mlbplayers.py` line 40
+
+## References
+
+- Issue #24, PR #38 in cal/paper-dynasty-database