使用默認值SQLAlchemy批量插入缺失值

Question

問題描述 -

我想使用SQLAlchemy批量插入幾百行。該模式看起來像下面

all_scrips_tbl = Table('all_scrips_info', _METADATA, Column('security_isin', String(16), primary_key=True), Column('company_name', String(80)), Column('nse_traded', Boolean, default=False), Column('nse_start_date', Date, default=datetime.date(year=2001, day=1, month=1)), Column('bse_traded', Boolean, default=False), Column('bse_start_date', Date, default=datetime.date(year=2001, day=1, month=1)), ) 現在每個憑證可以是 - nse_traded=True，bse_traded=True或兩者nse_traded=True and bse_traded=True

所以，我必須插入語句一樣 -

對於只有nse_traded=True ins = t.insert().values(security_isin=nstock.isin, company_name=nstock.name, nse_traded=True, nse_start_date=nstart_date, )

證券

對於只有bse_traded=True -

ins = t.insert().values(security_isin=bstock.isin, company_name=bstock.name, bse_traded=True, bse_start_date=bstart_date)

，並相應地爲nse_traded=True和bse_traded=True

我想批量插入這些語句。因此，像values().compile從創建語句的默認值是非常有用的，這樣我就可以使用下面 -

conn.execute(all_scrips_info.insert() , [ {}, {} ]) 凡類型的字典進行填充默認爲合適？

我也看過this的問題，但這與我的要求稍有不同。有一個old question on google groups這與我的要求相似。但是，sqlalchemy版本比較老，加上答案不是很容易理解。

我是否錯過了一些非常明顯的東西？

Answer 1

下面我提供瞭如何可以更容易地從一個CSV文件中的數據插入使用SQLAlchemy的數據庫的簡單例子。這裏的默認值是創建的日期。在init函數中，您可以添加更多邏輯......創建對象時應用此邏輯。

我想指出其他方法可用。例如，見SQLAlchemy的文檔：http://docs.sqlalchemy.org/en/latest/orm/persistence_techniques.html#bulk-operations

例子：

import csv 
from io import StringIO 
from sqlalchemy import Column, Integer, String, DateTime 
from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy import create_engine 
from sqlalchemy.orm import sessionmaker 
from datetime import datetime 

# Setting up model 

Base = declarative_base() 


class Car(Base): 
    __tablename__ = 'car' 

    id = Column('id', Integer, primary_key=True) 
    created = Column('created', DateTime, default=datetime.now()) 
    brand = Column(String(250)) 
    nr_gears = Column('nr_gears', Integer) 

    def __init__(self, brand, nr_gears): 
     self.brand = brand 
     self.nr_gears = nr_gears 

     # You can place logic,conditions here when creating the objects. Now only use of default date - creation 

    def __repr__(self): 
     return '{created}\t{brand} (nr of gears: {nr_gears})'.format(
      created=datetime.strftime(self.created, '%d/%m/%Y'), brand=self.brand, nr_gears=self.nr_gears) 


engine = create_engine('sqlite:///') 
session = sessionmaker() 
session.configure(bind=engine) 
ex_ses = session() 
Base.metadata.create_all(engine) 

# Reading in some dummy data 

csv_data = \ 
    '''Audi,5 
    BMW,5 
    Mercedes-Benz,5 
    Opel,5 
    Porsche,6 
    Volkswagen,5 
    Acura,5 
    Datsun,6 
    Honda,6 
    Infiniti,5 
    Isuzu,6 
    Lexus,5 
    Mazda,5 
    Mitsubishi,5 
    Nissan,5 
    Suzuki,6 
    Toyota,6 
    Subaru,6''' 

with StringIO(csv_data) as car_csv: 
    cars_data = [] 
    readCSV = csv.reader(car_csv, delimiter=',') 
    for row in readCSV: 
     # Add data to the session. 
     ex_ses.add(Car(brand=row[0], nr_gears=row[1])) 

ex_ses.commit() 

# Query 
cars = (ex_ses.query(Car).all()) 
print('Created\t\tBrand (nr of gears)') 
print('-' * 45) 
for car in cars: 
    print(car) 

# output: 
''' 
Created  Brand (nr of gears) 
--------------------------------------------- 
18/07/2017 Audi (nr of gears: 5) 
18/07/2017 BMW (nr of gears: 5) 
18/07/2017 Mercedes-Benz (nr of gears: 5) 
18/07/2017 Opel (nr of gears: 5) 
18/07/2017 Porsche (nr of gears: 6) 
18/07/2017 Volkswagen (nr of gears: 5) 
18/07/2017 Acura (nr of gears: 5) 
18/07/2017 Datsun (nr of gears: 6) 
18/07/2017 Honda (nr of gears: 6) 
18/07/2017 Infiniti (nr of gears: 5) 
18/07/2017 Isuzu (nr of gears: 6) 
18/07/2017 Lexus (nr of gears: 5) 
18/07/2017 Mazda (nr of gears: 5) 
18/07/2017 Mitsubishi (nr of gears: 5) 
18/07/2017 Nissan (nr of gears: 5) 
18/07/2017 Suzuki (nr of gears: 6) 
18/07/2017 Toyota (nr of gears: 6) 
18/07/2017 Subaru (nr of gears: 6) 
''' 

希望這有助於。基於我已經擴大低於汽車類的評論：

編輯。如果檔位數量丟失......則使用默認值9。當然，這是一個有限的例子，但（我希望）顯示，通過默認值工作的可能性......

class Car(Base): 
    __tablename__ = 'car' 

    id = Column('id', Integer, primary_key=True) 
    created = Column('created', DateTime, default=datetime.now()) 
    brand = Column(String(250)) 
    nr_gears = Column('nr_gears', Integer,default=None) 

    def __init__(self, brand, nr_gears): 
     self.brand = brand 

     if nr_gears is None or nr_gears == '': 
      nr_gears = 9 

     self.nr_gears = nr_gears 

     # You can place logic,conditions here when creating the objects. Now only use of default date - creation 

    def __repr__(self): 
     return '{created}\t{brand} (nr of gears: {nr_gears})'.format(
      created=datetime.strftime(self.created, '%d/%m/%Y'), brand=self.brand, nr_gears=self.nr_gears)