all_holdings
以下のコードでは、Accountを、holdings
を返すというプロパティに置き換えたいと思いますdesired_holdings
(これは、時間の経過とともに変化する可能性のある最新の既知の数量を表す保有物です)。私は関係への呼び出しを構築する方法を理解するのに苦労しています。
さらに、パターンの適切性(履歴データを単一のテーブルに保持し、最大日付サブクエリを使用して最新のものを取得する)、およびクエリのより良い代替案や改善についてのコメントをいただければ幸いです。
from sqlalchemy import Column, Integer, String, Date, DateTime, REAL, ForeignKey, func
from sqlalchemy.orm import relationship, aliased
from sqlalchemy.sql.operators import and_, eq
from sqlalchemy.ext.declarative import declarative_base
from db import session
import datetime
import string
Base = declarative_base()
class MySQLSettings(object):
__table_args__ = {'mysql_engine':'InnoDB'}
class Account(MySQLSettings, Base):
__tablename__ = 'account'
id = Column(Integer, primary_key=True)
name = Column(String(64))
all_holdings = relationship('Holding', backref='account')
def desired_holdings(self):
max_date_subq = session.query(Holding.account_id.label('account_id'),
Holding.stock_id.label('stock_id'),
func.max(Holding.as_of).label('max_as_of')). \
group_by(Holding.account_id, Holding.stock_id).subquery()
desired_query = session.query(Holding).join(Account,
Account.id==account.id).join(max_date_subq).\
filter(max_date_subq.c.account_id==account.id).\
filter(Holding.as_of==max_date_subq.c.max_as_of).\
filter(Holding.account_id==max_date_subq.c.account_id).\
filter(Holding.stock_id==max_date_subq.c.stock_id)
return desired_query.all()
def __init__(self, name):
self.name = name
class Stock(MySQLSettings, Base):
__tablename__ = 'stock'
id = Column(Integer, primary_key=True)
name = Column(String(64))
def __init__(self, name):
self.name = name
class Holding(MySQLSettings, Base):
__tablename__ = 'holding'
id = Column(Integer, primary_key=True)
account_id = Column(Integer, ForeignKey('account.id'), nullable=False)
stock_id = Column(Integer, ForeignKey('stock.id'), nullable=False)
quantity = Column(REAL)
as_of = Column(Date)
stock = relationship('Stock')
def __str__(self):
return "Holding(%f, '%s' '%s')"%(self.quantity, self.stock.name, str(self.as_of))
def __init__(self, account, stock, quantity, as_of):
self.account_id = account.id
self.stock_id = stock.id
self.quantity = quantity
self.as_of = as_of
if __name__ == "__main__":
ibm = Stock('ibm')
session.add(ibm)
account = Account('a')
session.add(account)
session.flush()
session.add_all([ Holding(account, ibm, 100, datetime.date(2001, 1, 1)),
Holding(account, ibm, 200, datetime.date(2001, 1, 3)),
Holding(account, ibm, 300, datetime.date(2001, 1, 5)) ])
session.commit()
print "All holdings by relation:\n\t", \
string.join([ str(h) for h in account.all_holdings ], "\n\t")
print "Desired holdings query:\n\t", \
string.join([ str(h) for h in account.desired_holdings() ], "\n\t")
実行時の結果は次のとおりです。
All holdings by relation:
Holding(100.000000, 'ibm' '2001-01-01')
Holding(200.000000, 'ibm' '2001-01-03')
Holding(300.000000, 'ibm' '2001-01-05')
Desired holdings query:
Holding(300.000000, 'ibm' '2001-01-05')