kemi

kemi is an add-on for SQLAlchemy that aims to make defining relations with declarative easier for the most common cases.

Consider this example from the SQLAlchemy docs:

class Customer(Base):
    __tablename__ = 'customer'
    id = Column(Integer, primary_key=True)
    name = Column(String)

    billing_address_id = Column(Integer, ForeignKey("address.id"))
    shipping_address_id = Column(Integer, ForeignKey("address.id"))

    billing_address = relationship("Address",
                    primaryjoin="Address.id==Customer.billing_address_id")
    shipping_address = relationship("Address",
                    primaryjoin="Address.id==Customer.shipping_address_id")

Using kemi, this can be written as:

class Customer(Base):
    name = Column(String)
    billing_address = relationship("Address")
    shipping_address = relationship("Address")

Things that kemi currently does:

• adds a __tablename__ if none is explicitely set on the class
• adds an id column if no primary key column is present
• adds foreign key columns for relationships if no foreign key columns are present
• adds primaryjoins to relationships if they're not set

To use kemi, you need to use its DeclarativeMeta class when you make a call to declarative_base:

from sqlalchemy.ext.declarative import declarative_base
from kemi import DeclarativeMeta

Base = declarative_base(metaclass=DeclarativeMeta)

class Customer(Base):
    name = Column(String)
    billing_address = relationship("Address")
    shipping_address = relationship("Address")