Fully upgrade SQLAlchemy with dynamic table generation

Question

I need to create many similar databases in different places in a for loop. At the beginning of the cycle, I create an engine for a new one path_sql_dbon disk.

    engine = sa.create_engine("sqlite:///{}".format(path_sql_db), echo=0, listeners=[util_sa.ForeignKeysListener()])
    Session = sa.orm.sessionmaker(bind=engine)
    session = Session()

Then I have my tables in several modules inherited from DB_Base that were defined in the external module;

from sqlalchemy.ext.declarative import declarative_base
DB_Base = declarative_base()

The problem is that during my next iteration of the for loop, I can’t create my tables as they still exist somewhere?

InvalidRequestError: Table 'vector_var01' is already defined for this MetaData instance.  
Specify 'extend_existing=True' to redefine options and columns on an existing Table object.

I tried to use MetaData.drop_all () from the engine;

meta = sa.MetaData(bind = engine)
meta.reflect()
meta.drop_all()
session.close()

And also from the base;

DB_Base.metadata.bind = engine
DB_Base.metadata.reflect()
DB_Base.metadata.drop_all()

Without success, I was still just spinning in the dark.

Which instance of MetaData is an error? How can I completely reset the state of my database code?

EDIT

, . ORM. , .

, ;

from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
Base = declarative_base()

class Foo(Base):
    __tablename__ = 'foo'
    id = Column(Integer, primary_key=True)
    name = Column(String(50))

def generate_variable_table_class(name):
    """This is a helper function which dynamically creates a new ORM enabled class
    The table will hold the individual values of each variable
    Individual values are stored as a string
    """

    class NewTable( Base ):
        __tablename__ = "vector_{}".format(name)
        id = Column(Integer, primary_key=True)
        value = Column(String(16), nullable=False, unique=True)
        def __init__(self,value):
            self.value = str(value)

        def __str__(self):
            return self.value

        def __repr__(self):
            return self.value    


    NewTable.__name__ = "vector_ORM_{}".format(name)

    return NewTable


if __name__ == "__main__":

    for name in 'asfd', 'jkl', 'xyz':
        print("For loop: ",name)
        engine = create_engine(r'sqlite:///c:\testdelete\{}.sql'.format(name))
        Base.metadata.create_all(engine)
        Session = sessionmaker(bind=engine)
        session = Session()

        bunch_o_foos = [Foo(name = i) for i in range(10)]
        session.add_all(bunch_o_foos)
        session.commit()
        for foo in bunch_o_foos:
            print(foo.id)


        variables = [generate_variable_table_class(i) for i in range(10)]

, ; Python SQLAlchemy. ?

Answer 1

:

from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

class Foo(Base):
    __tablename__ = 'foo'
    id = Column(Integer, primary_key=True)
    name = Column(String(50))

for name in 'asfd', 'jkl', 'xyz':
    engine = create_engine('sqlite:///{}'.format(name))
    Base.metadata.create_all(engine)

. drop_all , , , . bind, . :

Base.metadata.bind = engine
Base.metadata.create_all()

.

, , (, vector_0), Base, MetaData, .

• , generate_variable_table_class .

• , Base (.. Foo !) ( , generate_variable_table_class create_all )

• sqlalchemy , NewTable. ORM , NewTable, __name__ . (. " " ).

• . declarative_base metaclass, . , __name__ = "vector_ORM_{}".format(name) NewTable. __qualname__, sqlalchemy .

from sqlalchemy.ext.declarative import declarative_base, DeclarativeMeta

class NamingDeclarativeMeta(DeclarativeMeta):
    def __init__(cls, classname, bases, dict_):
        if '__name__' in cls.__dict__:
            cls.__name__ = classname = cls.__dict__['__name__']
        DeclarativeMeta.__init__(cls, classname, bases, dict_)

Base = declarative_base(metaclass=NamingDeclarativeMeta)