SQLAlchemy classes across files

by

The simplest solution to your problem will be to take Base out of the module that imports A, B and C; Break the cyclic import.

base.py

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

a.py

from sqlalchemy import *
from base import Base
from sqlalchemy.orm import relationship

class A(Base):
    __tablename__ = "A"
    id  = Column(Integer, primary_key=True)
    Bs  = relationship("B", backref="A.id")
    Cs  = relationship("C", backref="A.id")

b.py

from sqlalchemy import *
from base import Base

class B(Base):
    __tablename__ = "B"
    id    = Column(Integer, primary_key=True)
    A_id  = Column(Integer, ForeignKey("A.id"))

c.py

from sqlalchemy import *
from base import Base

class C(Base):
    __tablename__ = "C"    
    id    = Column(Integer, primary_key=True)
    A_id  = Column(Integer, ForeignKey("A.id"))

main.py

from sqlalchemy import create_engine
from sqlalchemy.orm import relationship, backref, sessionmaker

import base


import a
import b
import c

engine = create_engine("sqlite:///:memory:")
base.Base.metadata.create_all(engine, checkfirst=True)
Session = sessionmaker(bind=engine)
session = Session()

a1 = a.A()
b1 = b.B()
b2 = b.B()
c1 = c.C()
c2 = c.C()

a1.Bs.append(b1)
a1.Bs.append(b2)    
a1.Cs.append(c1)
a1.Cs.append(c2)    
session.add(a1)
session.commit()

Works on my machine:

$ python main.py ; echo $?
0

More Related Contents:

  1. Does SQLAlchemy have an equivalent of Django’s get_or_create?
  2. How to write DataFrame to postgres table
  3. Speeding up pandas.DataFrame.to_sql with fast_executemany of pyODBC
  4. CS50: LIKE operator, variable substitution with % expansion
  5. Group by & count function in sqlalchemy
  6. Debugging (displaying) SQL command sent to the db by SQLAlchemy
  7. Flask-SQLalchemy update a row’s information
  8. Efficiently updating database using SQLAlchemy ORM
  9. SQLAlchemy ORDER BY DESCENDING?
  10. SQLAlchemy ON DUPLICATE KEY UPDATE
  11. stored procedures with sqlAlchemy
  12. SqlAlchemy – Filtering by Relationship Attribute
  13. How can I profile a SQLAlchemy powered application?
  14. sqlalchemy: create relations but without foreign key constraint in db?
  15. sqlalchemy.exc.NoSuchModuleError: Can’t load plugin: sqlalchemy.dialects:postgres
  16. Strange SQLAlchemy error message: TypeError: ‘dict’ object does not support indexing
  17. Getting first row from sqlalchemy
  18. ImportError: No module named sqlalchemy
  19. Getting random row through SQLAlchemy
  20. Select NULL Values in SQLAlchemy
  21. How to delete a table in SQLAlchemy?
  22. How to update sqlalchemy orm object by a python dict
  23. Trigger in sqlachemy
  24. ImportError: cannot import name ‘_ColumnEntity’ from ‘sqlalchemy.orm.query’
  25. SQLAlchemy: filtering on values stored in nested list of the JSONB field
  26. How to prevent UUID primary key for new SQLAlchemy objects being created with the same value
  27. Retrieve query results as dict in SQLAlchemy
  28. VALUES clause in SQLAlchemy
  29. How can I achieve a self-referencing many-to-many relationship on the SQLAlchemy ORM back referencing to the same attribute?
  30. flask sqlalchemy query with keyword as variable

Leave a Comment