SQLAlchemy is a popular database framework that provides an ORM and a schema centric query language, and in this talk we will take a look how to get started with the ORM. We'll learn how to establish connections to popular databases such as PostgreSQL and MySQL. Then we will look at how to define our models as user classes including relationships and persist them to the database. Next, we'll cover the how the SQLAlchemy session works with typical create, update, read, and delete operations. We'll wrap up with pointers of where to go next to learn more.

1. INTRODUCTION TO
SQLALCHEMY ORM
Created by /Jason A Myers @jasonamyers

2. WARNING!

3. SQLALCHEMY
Core - Schema centric
ORM - User Model

4. INSTALLING
pip install sqlalchemy

5. CONNECTING AND ESTABLISHING A
SESSION

6. CONNECTING
from sqlalchemy import create_engine
engine = create_engine('sqlite:///:memory:')

7. ESTABLISHING A SESSION
from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind=engine)
session = Session()

8. DEFINING MODELS

9. MODEL BASE
Declarative Base
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

10. COOKIE MODEL
from sqlalchemy import Column, Integer, Numeric, String
class Cookie(Base):
__tablename__ = 'cookies'
cookie_id = Column(Integer, primary_key=True)
cookie_name = Column(String(50), index=True)
cookie_recipe_url = Column(String(255))
cookie_sku = Column(String(55))
quantity = Column(Integer())
unit_cost = Column(Numeric(12, 2))

11. PERSISTING OUR TABLE
Base.metadata.create_all(engine)

12. INSERTING DATA

13. ADDING A COOKIE
cc_cookie = Cookie(cookie_name='chocolate chip',
cookie_recipe_url='http://some.aweso.me/cookie/recipe.html
cookie_sku='CC01',
quantity=12,
unit_cost=0.50)

14. ADDING TO SESSION
session.add(cc_cookie)
session.commit()

15. ACCESSING ATTRIBUTES
print(cc_cookie.cookie_id)
1

16. BULK INSERTS
c1 = Cookie(cookie_name='peanut butter',
cookie_recipe_url='http://some.aweso.me/cookie/peanut.html',
cookie_sku='PB01',
quantity=24,
unit_cost=0.25)
c2 = Cookie(cookie_name='oatmeal raisin',
cookie_recipe_url='http://some.okay.me/cookie/raisin.html',
cookie_sku='EWW01',
quantity=100,
unit_cost=1.00)
session.bulk_save_objects([c1,c2])
session.commit()

17. BULK INSERT DIFFERENCES
c1.cookie_id

18. QUERIES

19. ALL THE COOKIES!
cookies = session.query(Cookie).all()
print(cookies)
[Cookie(cookie_name='chocolate chip',
cookie_recipe_url='http://some.aweso.me/cookie/recipe.html',
cookie_sku='CC01', quantity=12, unit_cost=0.50),
Cookie(cookie_name='peanut butter',
cookie_recipe_url='http://some.aweso.me/cookie/peanut.html',
cookie_sku='PB01', quantity=24, unit_cost=0.25),
Cookie(cookie_name='oatmeal raisin',
cookie_recipe_url='http://some.okay.me/cookie/raisin.html',
cookie_sku='EWW01', quantity=100, unit_cost=1.00)]

20. ALL THE COOKIES! - ITERATOR
for cookie in session.query(Cookie):
print(cookie)
Cookie(cookie_name='chocolate chip',
cookie_recipe_url='http://some.aweso.me/cookie/recipe.html',
cookie_sku='CC01', quantity=12, unit_cost=0.50)
Cookie(cookie_name='peanut butter',
cookie_recipe_url='http://some.aweso.me/cookie/peanut.html',
cookie_sku='PB01', quantity=24, unit_cost=0.25)
Cookie(cookie_name='oatmeal raisin',
cookie_recipe_url='http://some.okay.me/cookie/raisin.html',
cookie_sku='EWW01', quantity=100, unit_cost=1.00)

21. PARTICULAR ATTRIBUTES
print(session.query(Cookie.cookie_name, Cookie.quantity).first())
('chocolate chip', 12)

22. ORDER BY
for cookie in session.query(Cookie).order_by(Cookie.quantity):
print('{:3} - {}'.format(cookie.quantity, cookie.cookie_name))
12 - chocolate chip
24 - peanut butter
100 - oatmeal raisin

23. DECENDING
from sqlalchemy import desc
for cookie in session.query(Cookie).order_by(desc(Cookie.quantity)):
print('{:3} - {}'.format(cookie.quantity, cookie.cookie_name))

24. LIMITING
query = session.query(Cookie).order_by(Cookie.quantity).limit(2)
print([result.cookie_name for result in query])
['chocolate chip', 'peanut butter']

25. DATABASE FUNCTIONS
from sqlalchemy import func
inv_count = session.query(func.sum(Cookie.quantity)).scalar()
print(inv_count)
136

26. DATABASE FUNCTIONS COUNT
rec_count = session.query(func.count(Cookie.cookie_name)).first()
print(rec_count)
(3, 0)

27. LABELING
rec_count = session.query(func.count(Cookie.cookie_name)
.label('inventory_count')).first()
print(rec_count.keys())
print(rec_count.inventory_count)
['inventory_count']
5

28. FILTER_BY
record = session.query(Cookie).
filter_by(cookie_name='chocolate chip').first()
print(record)
Cookie(cookie_name='chocolate chip',
cookie_recipe_url='http://some.aweso.me/cookie/recipe.html',
cookie_sku='CC01', quantity=12, unit_cost=0.50)

29. FILTER
record = session.query(Cookie).
filter(Cookie.cookie_name == 'chocolate chip').first()
print(record)

30. CLAUSEELEMENTS
query = session.query(Cookie).filter(
Cookie.cookie_name.like('%chocolate%'))
for record in query:
print(record.cookie_name)
chocolate chip

31. CLAUSEELEMENT METHODS

32. between(cleft, cright) - Find where the column is between
cleft and cright
distinct() - Find only unique values for column
in_([list]) - Find where the column is in the list
is_(None) - Find where the column is None (commonly
used for Null checks with None)
contains('string') - Find where the column has 'string' in it
(Case-sensitive)
endswith('string') - Find where the column ends with
'string' (Case-sensitive)
startswith('string') - Find where the column begins with
'string' (Case-sensitive)
ilike('string') - Find where the column is like 'string' (NOT
Case-sensitive)

33. OPERATORS
from sqlalchemy import cast
query = session.query(Cookie.cookie_name,
cast((Cookie.quantity * Cookie.unit_cost),
Numeric(12,2)).label('inv_cost'))
for result in query:
print('{} - {}'.format(result.cookie_name, result.inv_cost))
chocolate chip - 6.00
peanut butter - 6.00
oatmeal raisin - 100.00

34. CONJUNCTIONS
from sqlalchemy import and_, or_, not_
query = session.query(Cookie).filter(
or_(
Cookie.quantity.between(10, 50),
Cookie.cookie_name.contains('chip')
)
)
for result in query:
print(result.cookie_name)
chocolate chip
peanut butter

35. UPDATING COOKIES

36. UPDATING COOKIES
query = session.query(Cookie)
cc_cookie = query.filter(Cookie.cookie_name == "chocolate chip").first()
cc_cookie.quantity = cc_cookie.quantity + 120
session.commit()
print(cc_cookie.quantity)
132

37. DELETING COOKIES

38. DELETING COOKIES
query = session.query(Cookie)
query = query.filter(Cookie.cookie_name == "peanut butter")
dcc_cookie = query.one()
session.delete(dcc_cookie)
session.commit()
dcc_cookie = query.first()
print(dcc_cookie)
None

39. OKAY TIME FOR A BREATHER

40. RELATIONSHIPS

41. IMPORTS
from datetime import datetime
from sqlalchemy import DateTime, ForeignKey, Boolean
from sqlalchemy.orm import relationship, backref

42. USER MODEL
class User(Base):
__tablename__ = 'users'
user_id = Column(Integer(), primary_key=True)
username = Column(String(15), nullable=False, unique=True)
email_address = Column(String(255), nullable=False)
phone = Column(String(20), nullable=False)
password = Column(String(25), nullable=False)
created_on = Column(DateTime(), default=datetime.now)
updated_on = Column(DateTime(), default=datetime.now, onupdate=datetime.n

43. ORDER MODEL
class Order(Base):
__tablename__ = 'orders'
order_id = Column(Integer(), primary_key=True)
user_id = Column(Integer(), ForeignKey('users.user_id'))
shipped = Column(Boolean(), default=False)
user = relationship("User", backref=backref('orders', order_by=order_id)

44. LINEITEM MODEL
class LineItem(Base):
__tablename__ = 'line_items'
line_item_id = Column(Integer(), primary_key=True)
order_id = Column(Integer(), ForeignKey('orders.order_id'))
cookie_id = Column(Integer(), ForeignKey('cookies.cookie_id'))
quantity = Column(Integer())
extended_cost = Column(Numeric(12, 2))
order = relationship("Order", backref=backref('line_items', order_by=line
cookie = relationship("Cookie", uselist=False)

45. PERSIST THEM
Base.metadata.create_all(engine)

46. DEFINING A USER
cookiemon = User(username='cookiemon',
email_address='mon@cookie.com',
phone='111-111-1111',
password='password')
session.add(cookiemon)
session.commit()

47. SETTING UP AN ORDER
o1 = Order()
o1.user = cookiemon
session.add(o1)

48. PREPARING LINE ITEMS
cc = session.query(Cookie).filter(Cookie.cookie_name ==
"chocolate chip").one()
line1 = LineItem(cookie=cc, quantity=2, extended_cost=1.00)
pb = session.query(Cookie).filter(Cookie.cookie_name ==
"oatmeal raisin").one()
line2 = LineItem(quantity=12, extended_cost=3.00)
line2.cookie = pb

49. ASSOCIATE ORDER AND LINE ITEMS
o1.line_items.append(line1)
o1.line_items.append(line2)
session.commit()

50. USING RELATIONSHIPS IN QUERIES
query = session.query(Order.order_id, User.username, User.phone,
Cookie.cookie_name, LineItem.quantity,
LineItem.extended_cost)
query = query.join(User).join(LineItem).join(Cookie)
results = query.filter(User.username == 'cookiemon').all()
print(results)
[(1, 'cookiemon', '111-111-1111', 'chocolate chip', 2, Decimal('1.00')),
(1, 'cookiemon', '111-111-1111', 'oatmeal raisin', 12, Decimal('3.00'

51. ANOTHER EXAMPLE
query = session.query(User.username, func.count(Order.order_id))
query = query.outerjoin(Order).group_by(User.username)
for row in query:
print(row)
('cookiemon', 1)

52. WHAT OTHER THINGS ARE OUT
THERE?
Automap
Geospatial Queries

53. QUESTIONS
Jason Myers / @jasonamyers / Essential SQLAlchemy