41 lines
1.3 KiB
Python
41 lines
1.3 KiB
Python
"""Random-sample query for the showcase.
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Uses the tsm_system_rows TABLESAMPLE method (migration 0004) instead of
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ORDER BY random(): sampling cost scales with the sample size, not the table,
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so it stays fast as the collection grows. SYSTEM_ROWS(n) returns up to n
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rows; an empty table yields none.
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"""
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from sqlalchemy import select, text
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from sqlalchemy.ext.asyncio import AsyncSession
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from ..models import ImageRecord
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from .gallery_service import thumbnail_url
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class ShowcaseService:
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def __init__(self, session: AsyncSession):
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self.session = session
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async def random_sample(self, limit: int = 60) -> list[dict]:
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if limit < 1 or limit > 200:
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raise ValueError("limit must be between 1 and 200")
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stmt = select(ImageRecord).from_statement(
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text(
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"SELECT * FROM image_record "
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"TABLESAMPLE SYSTEM_ROWS(:n)"
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).bindparams(n=limit)
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)
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rows = (await self.session.execute(stmt)).scalars().all()
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return [
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{
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"id": r.id,
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"sha256": r.sha256,
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"mime": r.mime,
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"width": r.width,
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"height": r.height,
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"thumbnail_url": thumbnail_url(r.sha256, r.mime),
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}
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for r in rows
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]
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