SQLAlchemy：如何从祖父母那里获取孙子属性？答案

【问题标题】：SQLAlchemy: How to get grandchild attributes from grandparent?SQLAlchemy：如何从祖父母那里获取孙子属性？
【发布时间】：2016-12-15 16:44:33
【问题描述】：

每个League 有多个赛季，每个Season 有多个球队，每个Team 表有一个goals_for 列。

假设我想计算一个联赛中的所有goals_for所有球队，跨越所有个赛季。但我什至无法在赛季内访问球队。

以下返回一个 League 类型的项目：

get_teams_for_leagues = League.query.join(League.seasons).join(Season.teams).all()
print(get_teams_for_leagues)

如何从League 访问teams？

class League(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    full_name = db.Column(db.String, nullable=False)

    # One side of many to one with Season
    seasons = relationship("Season", back_populates="league", lazy='joined')

    def __repr__(self):
        return '<League %r>' % (self.full_name)

class Season(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    season_string_form = db.Column(db.String, nullable=False)

    # Many side of many to one wih Season
    league_id = db.Column(db.Integer, ForeignKey('league.id'))
    league = relationship("League", back_populates="seasons")

    # One side of many to one with Team
    teams = relationship("Team", back_populates="season")

    def __repr__(self):
        return '<Season %r>' % (self.id)


class Team(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String, nullable=False)
    goals_for = db.Column(db.Integer, nullable=False)

    # Many side of many to one with Season
    season_id = db.Column(db.Integer, ForeignKey('season.id'))
    season = relationship("Season", back_populates="teams")

    def __repr__(self):
        return '<Team %r>' % (self.name)

【问题讨论】：

你的模型是什么样的？请为其添加代码。
@MrLeeh 完成。谢谢。

标签： python sql flask sqlalchemy flask-sqlalchemy

【解决方案1】：

可能只是做一个聚合，比如：

from sqlalchemy.sql import func

res = db_session.query(func.sum(Team.goals_for), Team.name)\
         .join(Season).join(League)\
         .filter(League.full_name = 'La Liga')\
         .group_by(Team.name).all()

【讨论】：