dal.py 文件源码

def get_conversion_candidate(ebook_id, to_format):     
    to_format_id = await get_format_id(to_format)
    async with engine.acquire() as conn:
        source = model.Source.__table__
        format = model.Format.__table__
        res = await conn.execute(select([source.c.id, format.c.extension]).where(and_(source.c.ebook_id == ebook_id,
                                                                  source.c.format_id == to_format_id,
                                                                  source.c.format_id == format.c.id))\
                                 .order_by(nullslast(desc(source.c.quality))))
        res = await res.first()  
        if res:
            return res.as_tuple()

        #TODO: Consider optimal selection of the source 
        # in previous version we first selected format (from available convertable in ebook)
        # and then one with best quality -   so actually the other way around  
        q=select([source.c.id, format.c.extension])\
        .where(and_(source.c.format_id == format.c.id, source.c.ebook_id == ebook_id)).order_by(nullslast(desc(source.c.quality)))
        async for row in conn.execute(q):
            if row.extension in settings.CONVERTABLE_TYPES:
                return row.id, row.extension

        return None, None