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fix: batch story item counts in list_stories to eliminate N+1 #663

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fix: batch story item counts in list_stories to eliminate N+1 #663

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18 changes: 15 additions & 3 deletions backend/services/stories.py
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Original file line number Diff line number Diff line change
Expand Up @@ -125,12 +125,24 @@ async def list_stories(
"""
stories = db.query(DBStory).order_by(DBStory.updated_at.desc()).all()

if not stories:
return []

# Batch-fetch all story item counts in one query to avoid an N+1 pattern
# (previously there was one COUNT query per story in the loop below).
story_ids = [s.id for s in stories]
count_rows = (
db.query(DBStoryItem.story_id, func.count(DBStoryItem.id).label("cnt"))
.filter(DBStoryItem.story_id.in_(story_ids))
.group_by(DBStoryItem.story_id)
.all()
)
item_counts = {row.story_id: row.cnt for row in count_rows}

result = []
for story in stories:
item_count = db.query(func.count(DBStoryItem.id)).filter(DBStoryItem.story_id == story.id).scalar()

response = StoryResponse.model_validate(story)
response.item_count = item_count
response.item_count = item_counts.get(story.id, 0)
result.append(response)

return result
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