0
在下面的代碼我想更換* all_holdings *在帳戶中有一個叫做財產持有返回的* desired_holdings *（這是表示最新的已知量增持其可以隨時間變化）。我無法弄清楚如何構建關係調用。SQLAlchemy的 - 如何查詢轉換與子查詢到關係
另外在圖案的恰當任何意見（在一個表中保存的歷史數據，並使用最大日期子查詢以獲得最新的），更好的替代品，在查詢的改進表示讚賞。
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")
結果時運行是：
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')