orms.md

Object-Relational Mappers (ORMs)

Comparing ActiveRecord in Ruby/Rails with SQLAlchemy in Python

Creation of Tables - Mapping a Class

ActiveRecord:

Best quote about ActiveRecord: "Magic is not inherently a bad word"
(http://api.rubyonrails.org/files/activerecord/README_rdoc.html)
Automated mapping between classes and tables, attributes and columns.

class Product < ActiveRecord::Base
end

The Product class is automatically mapped to the table named "products", which might look like this:

CREATE TABLE products (
  id int(11) NOT NULL auto_increment,
  name varchar(255),
  PRIMARY KEY  (id)
);

This would also define the following accessors: Product#name and Product#name=(new_name)

SQLAlchemy:

SQLAlchemy uses Declarative base (less magic, but still lots going on under the hood [1]).
You have to explicitly import classes from the SQLAlchemy library (even things like data types!)

http://docs.sqlalchemy.org/en/rel_0_9/orm/extensions/declarative.html

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String

Base = declarative_base()
class SomeClass(Base):
    __tablename__ = 'some_table'
    id = Column(Integer, primary_key=True)
    name =  Column(String(50))

[1] *Specifically, the creation of a Table and mapper() objects.

Connecting to database

ActiveRecord:

connect to SQLite3

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: 'dbfile.sqlite3')

# connect to MySQL with authentication
ActiveRecord::Base.establish_connection(
    adapter:  'mysql2',
    host:     'localhost',
    username: 'me',
    password: 'secret',
    database: 'activerecord'
)