如何使用SQLAlchemy对* count *子查询求和? [英] How to sum *count* subqueries with SQLAlchemy?

问题描述

我的数据库中有以下模型(Flask-SQLALchemy，声明性方法，已简化):

I have the following models in my DB (Flask-SQLALchemy, declarative approach, simplified):

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'))

每局比赛都可能赢，输或平局.我需要让玩家按获胜率"对他们进行排序-即:

Each game may be either won, lost or ended in draw. I need to get players sorting them by "win rate" - i.e.:

• 如果玩家创建了游戏，而游戏的获胜者是 creator ，则视为获胜；
• 如果玩家被邀请作为对手参加比赛，而游戏的获胜者是对手，则也视为获胜；
• 该玩家参加的其他游戏被视为输掉游戏.

• if player created a game and that game's winner is creator, it is considered win;
• if the player was invited to game as opponent and game's winner is opponent, it is also considered win;
• other games where this player participated are considered lost games.

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

当我要确定特定玩家的获胜率时，此方法有效.但是当我想按获胜率对玩家进行排序时，它失败了.我试图用SQL重写它，并得到了这样的内容:

This approach works when I want to determine win rate for particular player; but it fails when I want to sort players by win rate. I tried to rewrite it in SQL and got something like this:

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)
)

这不能处理没有游戏的玩家，但应该可以正常工作.没有游戏的玩家可能可以使用MySQL CASE 语句来处理.

This doesn't handle players without games but should work in general. Players without games can be probably handled with MySQL CASE statement.

但是问题是我无法弄清楚如何使用SQLAlchemy对该SQL进行编码.这是我尝试使用的(简化)代码:

But the problem is that I cannot figure how do I encode this SQL using SQLAlchemy. Here is a (simplified) code I try to use:

@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
    ))

当涉及到 won/count 行时，此代码失败，告诉我 Query 不能被 Query 除以.我尝试使用子查询，但没有成功.

This code fails when it comes to won / count line telling me that Query cannot be divided by Query. I tried using subqueries but without any success.

我应该如何实施?还是我应该使用某种联接/无论使用什么?(无法更改数据库方案.)

How should I implement it? Or maybe I should use some kind of joins/whatever? (DB scheme cannot be changed.)

推荐答案

尝试使用核心表达式而不是orm查询:

Try working with core expressions instead of orm queries:

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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