有条件的sqlalchemy查询以进行加载

Question

我有4个表，分别称为文件元数据，播放器排名，统计数据功能和演示功能。一个文件元数据可以具有多个播放器等级（每个播放器等级代表一个播放器），并且一个播放器等级可以具有统计功能或演示功能（如果is_demo为true，则两者都可以）。我需要有效地将播放器状态（即统计功能或演示功能）（如果文件元数据中的is_demo标志为true，请获取演示功能，否则为统计功能）读取到熊猫数据框。

现在是我的查询：

session = self.session()
query = session.query(self.db_model.file_metadata)
query = query.options(
        joinedload(self.db_model.file_metadata.player_rank)                         
        .joinedload(self.db_model.player_rank.stat_features))\            
        .options(joinedload(self.db_model.file_metadata.player_rank)                 
        .joinedload(self.db_model.player_rank.demo_features))
query = query.filter(case(
                    [
                     (self.db_model.file_metadata.is_demo is True, 
                      self.db_model.player_rank.demo_features),
                    ],
                    else_=self.db_model.player_rank.stat_features
                ))

chunks = pd.read_sql(query.statement, con=query.session.bind, 
                     chunksize=100)
df = pd.DataFrame()
   for chunk in tqdm(chunks):
      df = pd.concat([df, chunk])
session.close()

数据库设计：

class file_metadata(base):
    __tablename__ = 'file_metadata'

    unique_identifier = Column(BigInteger, primary_key=True)
    filename = Column(String, unique=True)
    date = Column(DateTime)
    is_demo = Column(Boolean)
    version = Column(String)  # version of analyzer
    server_type = Column(String)
    tie_situation = Column(Boolean)
    player_ranks = relationship("player_rank", lazy='subquery',
                                back_populates="file_metadata", uselist=True,
                                cascade="delete")


class player_rank(base):
    __tablename__ = 'player_rank'

    # id = Column(Integer, primary_key=True)
    Date = Column(BigInteger, primary_key=True)
    Name = Column(String, primary_key=True)
    mu = Column(Float(precision=3))
    sigma = Column(Float(precision=3))
    Won = Column(Integer)
    file_metadata_id = Column(BigInteger, ForeignKey('file_metadata.unique_identifier'))
    file_metadata = relationship("file_metadata", lazy='subquery',
                                 back_populates="player_ranks", uselist=False)
    stat_features = relationship("stat_features", lazy='subquery', uselist=False,
                                 back_populates="player_ranking")
    demo_features = relationship("demo_features", lazy='subquery',
                                 uselist=False, back_populates="player_ranking")


class stat_features(base, CommonEqualityMixin):
    __tablename__ = 'stat_features'

    id = Column(Integer, primary_key=True)
    Name = Column(String)
    Date = Column(BigInteger)
    Pistol_Rounds_Won_Percentage = Column(Float(precision=3))
    HS_Percentage = Column(Float(precision=3))
    Clutches_Won = Column(Integer)
    ADR = Column(Float(precision=3))
    FPR = Column(Float(precision=3))
    APR = Column(Float(precision=3))
    K_D_Diff_Round = Column(Float(precision=3))
    Flash_Assists_Round = Column(Float(precision=3))
    Blind_Players_Killed_Round = Column(Float(precision=3))
    Blind_Kills = Column(Float(precision=3))
    Grenade_Damage_Round = Column(Float(precision=3))
    Fire_Damage_Round = Column(Float(precision=3))
    Time_Flashing_Opponents_Round = Column(Float(precision=3))
    Accuracy = Column(Float(precision=3))
    Num_Times_Trader = Column(Float(precision=3))
    Num_Times_Tradee = Column(Float(precision=3))
    KAST = Column(Float(precision=3))
    Ratings = Column(Float(precision=3), default=-1)
    Won = Column(Integer)
    player_ranking = relationship("player_rank", foreign_keys=[Name, Date], lazy='subquery',
                                  uselist=False, back_populates="stat_features")

    __table_args__ = (ForeignKeyConstraint([Name, Date], [player_rank.Name, player_rank.Date]),)



class demo_features(base, CommonEqualityMixin):
    __tablename__ = 'demo_features'

    id = Column(Integer, primary_key=True)
    Name = Column(String)
    Date = Column(BigInteger)
    Pistol_Rounds_Won_Percentage = Column(Float(precision=3))
    HS_Percentage = Column(Float(precision=3))
    Clutches_Won = Column(Integer)
    ADR = Column(Float(precision=3))
    FPR = Column(Float(precision=3))
    APR = Column(Float(precision=3))
    K_D_Diff_Round = Column(Float(precision=3))
    Flash_Assists_Round = Column(Float(precision=3))
    Blind_Players_Killed_Round = Column(Float(precision=3))
    Blind_Kills = Column(Float(precision=3))
    Grenade_Damage_Round = Column(Float(precision=3))
    Fire_Damage_Round = Column(Float(precision=3))
    Time_Flashing_Opponents_Round = Column(Float(precision=3))
    Accuracy = Column(Float(precision=3))
    Num_Times_Trader = Column(Float(precision=3))
    Num_Times_Tradee = Column(Float(precision=3))
    KAST = Column(Float(precision=3))
    Ratings = Column(Float(precision=3), default=-1)
    Won = Column(Integer)
    player_ranking = relationship("player_rank", foreign_keys=[Name, Date], lazy='subquery',
                                  uselist=False, back_populates="demo_features")

    __table_args__ = (ForeignKeyConstraint([Name, Date], [player_rank.Name, player_rank.Date]),)