kemi's Introduction

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")

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