[英]How to sum *count* subqueries with SQLAlchemy?
我的數據庫中有以下模型(Flask-SQLALchemy,聲明性方法,已簡化):
class Player(db.Model):
id = db.Column(db.Integer, primary_key = True)
...
class Game(db.Model):
id = db.Column(db.Integer, primary_key = True)
creator_id = db.Column(db.Integer, db.ForeignKey('player.id'))
creator = db.relationship(Player, foreign_keys='Game.creator_id')
opponent_id = db.Column(db.Integer, db.ForeignKey('player.id'))
opponent = db.relationship(Player, foreign_keys='Game.opponent_id')
winner = db.Column(db.Enum('creator', 'opponent'))
每場比賽可能贏,輸或平局。 我需要讓玩家按“獲勝率”對它們進行排序-即:
creator
,則視為獲勝; opponent
,則也視為獲勝; 所以我的算法如下:
@hybrid_property
def winrate(self):
games = Game.query.filter(or_(
Game.creator_id == self.id,
Game.opponent_id == self.id,
))
count = 0
wins = 0
for game in games:
count += 1
if game.creator_id == self.id and game.winner == 'creator':
wins += 1
elif game.opponent_id == self.id and game.winner == 'opponent':
wins += 1
if count == 0:
return 0
return wins / count
當我要確定特定玩家的獲勝率時,這種方法有效。 但是當我想按獲勝率對玩家進行排序時,它失敗了。 我試圖用SQL重寫它,並得到了這樣的內容:
SELECT * FROM player
ORDER BY ((SELECT count(g1.id) FROM game g1
WHERE g1.creator_id = player.id AND g1.winner = 'creator'
) + (SELECT count(g2.id) FROM game g2
WHERE g2.opponent_id = player.id AND g2.winner = 'opponent'
)) / (SELECT count(g3.id) FROM game g3
WHERE player.id IN (g3.creator_id, g3.opponent_id)
)
這不能處理沒有游戲的玩家,但應該可以正常工作。 沒有游戲的玩家可能可以使用MySQL CASE
語句來處理。
但是問題是我無法弄清楚如何使用SQLAlchemy對該SQL進行編碼。 這是我嘗試使用的(簡化)代碼:
@winrate.expression
def winrate(cls):
cnt = Game.query.filter(
cls.id.in_(Game.creator_id, Game.opponent_id)
).with_entities(func.count(Game.id))
won = Game.query.filter(
or_(
and_(
Game.creator_id == cls.id,
Game.winner == 'creator',
),
and_(
Game.opponent_id == cls.id,
Game.winner == 'opponent',
),
)
)
return case([
(count == 0, 0),
], else_ = (
won / count
))
當涉及won / count
行時,此代碼失敗,告訴我Query
不能被Query
。 我嘗試使用子查詢,但沒有成功。
我應該如何實施? 還是我應該使用某種聯接/其他方式? (無法更改數據庫方案。)
嘗試使用核心表達式而不是orm查詢:
class Player(..):
# ...
@winrate.expression
def _winrate(cls):
cnt = (
select([db.func.count(Game.id)])
.where(
db.or_(
Game.creator_id == cls.id,
Game.opponent_id == cls.id,
))
.label("cnt")
)
won = (
select([db.func.count(Game.id)])
.where(
db.or_(
db.and_(Game.creator_id == cls.id,
Game.winner == 'creator'),
db.and_(Game.opponent_id == cls.id,
Game.winner == 'opponent'),
))
.label("cnt")
)
return db.case(
[(cnt == 0, 0)],
else_ = db.cast(won, db.Numeric) / cnt
)
# ...
q = session.query(Player).order_by(Player.winrate.desc())
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