In this talk, we'll examine how to use SQLAlchemy ORM and Core in both simple queries and query builder type applications. Next, we'll explore Alembic database migrations and how we can use them to handle database changes.

1. SQLAlchemy and
Alembic
ORM, Core and Migrations
/Jason Myers @jasonamyers

3. Architecture

5. pip install sqlalchemy
pip install flask-sqlalchemy
bin/paster create -t pyramid_alchemy tutorial

6. from sqlalchemy import create_engine
engine = create_engine(
‘dialect+driver://USER:PASS@HOST:PORT/DB’
)

7. Porcelain

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

11. from sqlalchemy import (
Column,
Integer,
String,
Float
)
from sqlalchemy import ForeignKey
from sqlalchemy.orm import (
relationship,
backref
)

12. class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
fullname = Column(String)
balance = Column(Float)
group = Column(String)
addresses = relationship(
"Address",
order_by="Address.id",
backref="user"
)

13. def __init__(self, name, fullname, balance, group):
self.name = name
self.fullname = fullname
self.balance = balance
self.group = group

15. Base.metadata.create_all(engine)

17. from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind=engine)
db = Session()

18. user1 = User('Bob', 'Big Bob', 1000000.00, 'Mob')
user2 = User('Linda', 'Linda Lu', 100.50, 'Diner')
user3 = User('Lil Bob', 'Bobby Jr', 100500.00, 'Mob')
user4 = User('Rachael', 'Rachael Rach', 125.50, 'Personal')

19. db.add(user1)
db.commit()
db.delete(user1)

20. db.expunge(user1)
db.refresh(user1)
db.expire(user1)
db.rollback()

22. for user in db.query(User).all():
print user.name, user.balance
Out[1]: Bob 1000000.0

23. entries = db.session.query(Entries).filter_by(user_id=user.id)
.filter(Entries.entry_time >
(datetime.datetime.utcnow() - datetime.timedelta(30))
).order_by('ID DESC').all()

24. SELECT entries.id AS entries_id,
entries.user_id AS entries_user_id,
entries.phone AS entries_phone,
entries.measurement AS entries_measurement,
entries.insulin AS entries_insulin,
entries.insulin_type AS entries_insulin_type,
entries.carbs AS entries_carbs,
entries.tag AS entries_tag,
entries.three_sixty_id AS entries_three_sixty_id,
entries.entry_time AS entries_entry_time,
entries.created_time AS entries_created_time
FROM entries
WHERE entries.user_id = :user_id_1
AND entries.entry_time > :entry_time_1
ORDER BY ID DESC

25. from sqlalchemy import func
from sqlalchemy.sql import label
results = db.query(
User.group,
label('members', func.count(User.id)),
label(
'total_balance',
func.sum(User.balance)
)
).group_by(User.group).all()
for result in results:
print result.group,
result.members,
result.total_balance

27. bob.addresses.append(home_address)
bob.addresses
bob.addresses.filter(Address.type='H').one()

28. query = db.query(User, Address).filter(User.id==Address.user_id)
query = query.filter(Address.email_address=='jack@goog.com').all()

30. @hybrid_property
def grand_total(self):
rollup_fields = [
'merchandise_cost',
'tax',
'shipping',
]
total = sum([self.__getattribute__(x) for x in rollup_fields])
return round(total, 2)

32. Plumbing

33. from sqlalchemy import create_engine
engine = create_engine(
‘dialect+driver://USER:PASS@HOST:PORT/DB’
)

34. from sqlalchemy import (Table, Column,
Integer, String, MetaData, ForeignKey)
metadata = MetaData()
users = Table('users', metadata,
Column('id', Integer, primary_key=True),
Column('name', String),
Column('fullname', String),
)

35. Base.metadata.create_all(engine)
conn = engine.connect()

36. ins = users.insert().values(name='jack', fullname='Jack Bell')
result = conn.execute(ins)
ins = users.insert()
conn.execute(ins, id=2, name='wendy', fullname='Wendy McDonalds')

37. conn.execute(addresses.insert(), [
{'user_id': 1, 'email_address' : 'j@y.com'},
{'user_id': 1, 'email_address' : 'j@m.com'},
])

38. def build_table(table_name):
return Table(
table_name,
metadata,
autoload=True,
autoload_with=engine
)

39. build_table('census')
unavailable_fields = [
c.name for c in t.c if isinstance(c.type, NullType)
]

41. Informix
MS SQL
Oracle
Postgres
SQLite
Custom

42. class UnloadFromSelect(Executable, ClauseElement):
def __init__(self, select, bucket, access_key, secret_key):
self.select = select
self.bucket = bucket
self.access_key = access_key
self.secret_key = secret_key
@compiles(UnloadFromSelect)
def visit_unload_from_select(element, compiler, **kw):
return "unload ('%(query)s') to '%(bucket)s'
credentials 'aws_access_key_id=%(access_key)s;
aws_secret_access_key=%(secret_key)s' delimiter ','
addquotes allowoverwrite" % {
'query': compiler.process(element.select,
unload_select=True, literal_binds=True),
'bucket': element.bucket,
'access_key': element.access_key,
'secret_key': element.secret_key,
}

43. unload = UnloadFromSelect(
select([fields]),
'/'.join(['s3:/', BUCKET, filename]),
ACCESS_KEY,
SECRET_KEY
)

44. unload (
'select * from venue where venueid in (
select venueid from venue order by venueid desc limit 10)'
)
to 's3://mybucket/venue_pipe_'
credentials 'aws_access_key_id=ACCESS_KEY;
aws_secret_access_key=SECRET_KEY';

45. s = select(
[
t.c.race,
t.c.factor,
func.sum(g.t.c.value).label('summed')
], t.c.race > 0
).where(
and_(
t.c.type == 'POVERTY',
t.c.value != 0
)
).group_by(
t.c.race,
t.c.factor
).order_by(
t.c.race,
t.c.factor)

46. s = select(
[
table.c.discharge_year,
func.count(1).label(
'patient_discharges'),
table.c.zip_code,
], table.c.discharge_year.in_(years)
).group_by(table.c.discharge_year)
s = s.where(table.c.hospital_name == provider)
if 'total_charges' not in unavailable_fields:
s = s.column(
func.sum(table.c.total_charges
).label('patient_charges')
)
s = s.group_by(table.c.zip_code)
s = s.order_by('discharges DESC')
cases = conn.execute(s).fetchall()

48. pip install alembic

49. alembic init alembic

52. # A generic, single database configuration.
[alembic]
# path to migration scripts
script_location = alembic
# template used to generate migration files
# file_template = %%(rev)s_%%(slug)s
# set to 'true' to run the environment during
# the 'revision' command, regardless of
autogenerate
# revision_environment = false
sqlalchemy.url = driver://user:pass@localhost/dbname

53. from glu import db
target_metadata = db.metadata
def run_migrations_online():
alembic_config = config.get_section(config.config_ini_section)
from config import SQLALCHEMY_DATABASE_URI
alembic_config['sqlalchemy.url'] = SQLALCHEMY_DATABASE_URI
engine = engine_from_config(
alembic_config,
prefix='sqlalchemy.',
poolclass=pool.NullPool
)

55. alembic revision -m "initial"

56. def upgrade():
op.create_table('users_to_users',
sa.Column('patient_user_id', sa.Integer(), nullable=False),
sa.Column('provider_user_id', sa.Integer(), nullable=False),
sa.ForeignKeyConstraint(['patient_user_id'], ['users.id'],),
sa.ForeignKeyConstraint(['provider_user_id'], ['users.id'],),
sa.PrimaryKeyConstraint('patient_user_id','provider_user_id')
)
op.alter_column(u'reminders', u'user_created', nullable=True)

57. def downgrade():
op.alter_column(u'reminders', u'user_created',
existing_type=mysql.TINYINT(display_width=1), nullable=False
)
op.drop_table('users_to_users')

58. alembic upgrade head

59. alembic revision --autogenerate -m "Added account table"

60. Table (adds/removes)
Columns (adds/removes)
Nullable changes

62. Optionally: Column Type changes
compare_type=True
No Name changes on Columns or Table

64. alembic current
alembic upgrade +2
alembic downgrade -1
alembic upgrade ae1
alembic upgrade 1 --sql > file.sql
alembic history

65. 2806761df139 -> 1e9831c8fa7d (head), Adding tags to ...
2806761df139 -> 46a1d4de6e04 (head), Added timezone ...
4f7119855daf -> 2806761df139 (branchpoint), Added Pr...
377addf23edb -> 4f7119855daf, Added user_created to ...
483d9a63fbf5 -> 377addf23edb, Adding claimed to user...
464ba41d7ad8 -> 483d9a63fbf5, Adding username/passwo...
2cfd9dc89267 -> 464ba41d7ad8, Adding Intercom.io
d4774a3ce8 -> 2cfd9dc89267, Seperating Roles and Use...
None -> d4774a3ce8, Base

66. THE END
@jasonamyers