Question

在为sql alchemy定义类时是否可以避免键入列的名称和数据类型，例如假设您拥有：

from sqlalchemy import Column, Date, Integer, String, Numeric 
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Fruit(Base):

   __tablename__ = 'Fruits'

    # names and datatypes of columns
    date_of_record = Column(Date, primary_key=True)
    number_of_apples = Column(Integer)
    number_of_pears = Column(Integer)

是否可以使用循环重新创建最后一部分？例如，如果您想将列名和类型作为输入：

column_names = ['date_of_record', 'number_of_apples', 'number_of_pears']
column_types = [Date, Integer, Integer]

class Fruit(Base):

  __tablename__ = 'Fruits'

  def __init__(self, column_names, column_types):
        for index, (name, type) in enumerate(zip(column_names, column_types)):
            if index == 0:   
                setattr(self, name, Column(type, primary_key = True))
            else:
                setattr(self, name, Column(type))

但是这会引发ArgumentError：Mapper Mapper | Fruit | Fruits无法为映射表'Fruits'组装任何主键列

是否有人能够提供使用SQL炼金术时如何在类定义中使用列名和类型作为变量的工作示例？

Answer 1

实际上是的，您可以这样做，但是，您需要使用Table()和sqlalchemy.orm.mapper创建数据库。

您需要执行以下操作：

from sqlalchemy import create_engine, MetaData, Table, Column
from sqlalchemy import Integer, Date # Insert your types here
from sqlalchemy.orm import mapper

engine = create_engine('sqlite:///fruits.db') # Here you need to insert your own path to db

column_names = ['date_of_record', 'number_of_apples', 'number_of_pears']
column_types = [Date, Integer, Integer]

# Adding columns

columns = list()
for index, (name, type) in enumerate(zip(column_names, column_types)):
            if index == 0:   
                columns.append(Column(name, type, primary_key = True))
            else:
                columns.append(Column(name, type))

metadata = MetaData()
fruits_table  = Table('Fruits', metadata, *columns)
metadata.create_all(engine) # Create table

class Fruit(Base):
    # You can make initialization method here
    pass

print(mapper(Fruit, fruits_table)) # Create a Mapper and print it

现在，要进行会话，您需要执行以下操作：

from sqlalchemy.orm import sessionmaker

Session = sessionmaker(bind=engine) # Use an engine with your database
session = Session()

test_fruit = Fruit() # You can initialize it, if you will make __init__ method

test_fruit.number_of_apples = 2
test_fruit.number_of_pears = 3

session.add(test_fruit)
session.commit()

希望我的回答对您有所帮助！

定义类sql-alchemy：循环以分配列类型

1 个答案: