Python SQLAlchemy Change tablename in init

Question

I have 2 tables with the same column structure.

The script pulls from 2 different json sources with slightly different keys.

My Item class identifies the source and then parses the data.

In my Item class I want to be able to change the __tablename__ based on the data source.

Is this possible or do I need to write a separate class for each data source?

Thanks,

Code:

Base = declarative_base()


class Item(Base):
    __tablename__ = 'products'

    timestamp = Column(TIMESTAMP)
    itemid = Column(String, primary_key=True, index=True, unique=True)
    name = Column(String)    

    def __init__(self, item):

        if type(item) == Product_A:
            self.__tablename__ = "A_products"
            # Parse Data
        elif type(item) == Product_B:
            self.__tablename__ = "B_products"
            # Parse Data

nosklo · Accepted Answer · 2018-10-08 17:13:24Z

2

This is not a good idea, in sqlalchemy each class should be mapped to a single table. A solution is to make two classes and a free function to dispatch between them:

Base = declarative_base()
class Item_A(Base):
    __tablename__ = 'A_products'
    timestamp = Column(TIMESTAMP)
    itemid = Column(String, primary_key=True, index=True, unique=True)
    name = Column(String)    

class Item_B(Base):
    __tablename__ = 'B_products'
    timestamp = Column(TIMESTAMP)
    itemid = Column(String, primary_key=True, index=True, unique=True)
    name = Column(String)    

def create_item_object(item):
    if isinstance(item, Product_A):
        result = Item_A()
        #... more stuff
    elif isinstance(item, Product_B):
        result = Item_B()
        #... more stuff
    return result

answered Oct 8, 2018 at 17:13

nosklo

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