4. A model is blueprint.

5. from django.db import models
class User(models.Model):

6. from django.db import models
class User(models.Model):
email = models.EmailField(
max_length=254, unique=True, help_text='Used as the username')

7. from django.db import models
class User(models.Model):
email = models.EmailField(
max_length=254, unique=True, help_text='Used as the username')
name = models.CharField(max_length=50)

8. from django.db import models
class User(models.Model):
email = models.EmailField(
max_length=254, unique=True, help_text='Used as the username')
name = models.CharField(max_length=50)
phone = models.CharField(max_length=20, null=True, blank=True)

9. from django.db import models
class User(models.Model):
email = models.EmailField(
max_length=254, unique=True, help_text='Used as the username')
name = models.CharField(max_length=50)
phone = models.CharField(max_length=20, null=True, blank=True)
STATUS_PAID = 'paid'
STATUS_TRIALING = 'trialing'

10. from django.db import models
class User(models.Model):
email = models.EmailField(
max_length=254, unique=True, help_text='Used as the username')
name = models.CharField(max_length=50)
phone = models.CharField(max_length=20, null=True, blank=True)
STATUS_PAID = 'paid'
STATUS_TRIALING = 'trialing'
STATUS_CHOICES = (
(STATUS_PAID, 'Paid'),
(STATUS_TRIALING, 'Trialing'),
)

11. from django.db import models
class User(models.Model):
email = models.EmailField(
max_length=254, unique=True, help_text='Used as the username')
name = models.CharField(max_length=50)
phone = models.CharField(max_length=20, null=True, blank=True)
STATUS_PAID = 'paid'
STATUS_TRIALING = 'trialing'
STATUS_CHOICES = (
(STATUS_PAID, 'Paid'),
(STATUS_TRIALING, 'Trialing'),
)
status = models.CharField(
max_length=20, unique=True, choices=STATUS_CHOICES)

12. $ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=>

13. $ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> d accounts_user

14. $ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> d accounts_user
Table "public.accounts_user"
Column | Type | Modifiers
--------+------------------------+----------------------
id | integer | not null default ...
email | character varying(254) | not null
name | character varying(50) | not null
phone | character varying(20) |
status | character varying(20) | not null

15. class Message(models.Model):

16. class Message(models.Model):
sender = models.ForeignKey(
User)

17. $ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> d messaging_message

18. $ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> d messaging_message
Table "public.messaging_message"
Column | Type | Modifiers
-----------+---------+----------------------
id | integer | not null default ...
sender_id | integer | not null

19. $ ./manage.py shell_plus

20. $ ./manage.py shell_plus
In [1]: user = ...

21. $ ./manage.py shell_plus
In [1]: user = ...
In [2]: user.message_set.all()
Out[2]: [<Message: ...>, <Message: ...>]

22. class Message(models.Model):
sender = models.ForeignKey(
User)

23. class Message(models.Model):
sender = models.ForeignKey(
User, related_name='messages_sent')

24. $ ./manage.py shell_plus
In [1]: user = ...
In [2]: user.message_set.all()
Out[2]: [<Message: ...>, <Message: ...>]

25. $ ./manage.py shell_plus
In [1]: user = ...
In [2]: user.messages_sent.all()
Out[2]: [<Message: ...>, <Message: ...>]

27. Object-relational mapping

28. Model
User

29. Model
User
Manager
User.objects

30. Model
User
Manager
User.objects
Queryset
User.objects.all()
User.objects.filter(...)

31. Model
User
Manager
User.objects
Queryset
User.objects.all()
User.objects.filter(...)
eval via DB

32. Model
User
Manager
User.objects
Queryset
User.objects.all()
User.objects.filter(...)
Python List
list(User.objects
.all())
eval via DB

33. User.objects.all() # => queryset

34. User.objects.all() # => queryset
User.objects.filter(email='...') # => queryset

35. User.objects.all() # => queryset
User.objects.filter(email='...') # => queryset
User.objects.filter(email='...').count() # DB access

36. User.objects.filter(email='...')

37. User.objects.filter(email='...')
User.objects.filter(email='...', first_name='...')

38. User.objects.filter(email='...')
User.objects.filter(email='...', first_name='...')
User.objects.filter(email='...').filter(first_name='...')

39. User.objects.filter(email='...')
User.objects.filter(email='...', first_name='...')
User.objects.filter(email='...').filter(first_name='...')
first call creates
QuerySet from Manager

40. User.objects.filter(email='...')
User.objects.filter(email='...', first_name='...')
User.objects.filter(email='...').filter(first_name='...')
second call transforms
QuerySet into another
QuerySet
first call creates
QuerySet from Manager

41. User.objects.filter(email='...')

42. User.objects.filter(email='...').delete()

43. User.objects.filter(email='...').delete()
User.objects.delete()

44. User.objects.filter(email='...').delete()
User.objects.delete()

45. User.objects.filter(email='...').delete()
User.objects.delete()
User.objects.all().delete()

46. User.objects.filter(email='...').delete()
User.objects.delete()
User.objects.all().delete()
.delete() is only definedon QuerySet, not onManager (for safety)

48. from django.db.models import Q

49. from django.db.models import Q
User.objects.filter(Q(email='...'))

50. from django.db.models import Q
User.objects.filter(Q(email='...') | Q(first_name='...'))

51. from django.db.models import Q
is_user_query = Q(email='...') | Q(first_name='...')
User.objects.filter(is_user_query)

52. from django.db.models import Q
is_user_query = Q(email='...') | Q(first_name='...')
User.objects.filter(is_user_query)
transform search
criteria into
first-class value

53. User.objects.filter(customer_profile=cust_prof_instance)

54. User.objects.filter(customer_profile__id=123)

55. User.objects.filter(customer_profile__id__in=[123, 456])

56. User.objects.filter(customer_profile__isnull=False)

57. User.objects.filter(invitecodeusage__invite__code='...')

58. User.objects.filter(invitecodeusage__invite__code='...')
One-to-many: at least
one matching

60. users = Users.objects.filter(...)
for user in users:
for tm in user.tracked_metrics.all():
print tm.metric.key

61. users = Users.objects.filter(...)
for user in users:
for tm in user.tracked_metrics.all():
print tm.metric.key
Assume 10 users and16 distinct metrics

62. users = Users.objects.filter(...)
for user in users:
for tm in user.tracked_metrics.all():
print tm.metric.key
1 - users
10 - tracked metrics
16 - metrics

63. users = (Users.objects.filter(...)
.prefetch_related('tracked_metrics'))
for user in users:
for tm in user.tracked_metrics.all():
print tm.metric.key
1 - users
1 - tracked metrics
16 - metrics

64. users = (Users.objects.filter(...)
.prefetch_related('tracked_metrics__metric'))
for user in users:
for tm in user.tracked_metrics.all():
print tm.metric.key
1 - users
1 - tracked metrics
1 - metrics

66. users = (User.objects
.filter(customer_profile__isnull=False))
for user in users:
print user.customer_profile.uuid

67. users = (User.objects
.filter(customer_profile__isnull=False))
for user in users:
print user.customer_profile.uuid
Assume 10 users

68. users = (User.objects
.filter(customer_profile__isnull=False))
for user in users:
print user.customer_profile.uuid
1 - users
10 - customer profiles

69. users = (User.objects
.filter(customer_profile__isnull=False)
.prefetch_related('customer_profile'))
for user in users:
print user.customer_profile.uuid
1 - users
1 - customer profiles

70. users = (User.objects
.filter(customer_profile__isnull=False)
.select_related('customer_profile'))
for user in users:
print user.customer_profile.uuid
1 - users
0 - customer profiles
using JOIN

72. $ ./manage.py makemigrations

73. $ ./manage.py makemigrations
current
model
definition

74. $ ./manage.py makemigrations
current
model
definition
model definition
based on applied
migrations

75. $ ./manage.py makemigrations
current
model
definition
model definition
based on applied
migrations
DIFF

76. $ ./manage.py makemigrations
$ ./manage.py migrate

77. $ ./manage.py makemigrations
$ ./manage.py migrate
$ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=>

78. $ ./manage.py makemigrations
$ ./manage.py migrate
$ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> SELECT * FROM django_migrations;
id | app | name | applied
----+--------------+--------------+--------------------------
1 | accounts | 0001_initial | 2016-08-30 11:56:29.798795-07
(1 row)

79. $ ./manage.py migrate accounts 0002 # to specific version

80. $ ./manage.py migrate accounts 0002 # to specific version
$ ./manage.py migrate accounts 0001 # rollback

81. $ ./manage.py migrate accounts 0002 # to specific version
$ ./manage.py migrate accounts 0001 # rollback
$ ./manage.py migrate accounts 0002 --fake # only add to table

82. vida=> -- faking a migration
vida=>

83. vida=> -- faking a migration
vida=> INSERT INTO django_migrations (app, name, applied)
VALUES ('accounts', '0003_faked', current_timestamp);

85. class User(BaseModel):
email = models.EmailField(max_length=254, unique=True)
- phone_number = models.CharField(max_length=50)

86. class User(BaseModel):
email = models.EmailField(max_length=254, unique=True)
- phone_number = models.CharField(max_length=50)
+class Migration(migrations.Migration):
+ operations = [
+ migrations.RemoveField(
+ model_name='user',
+ name='phone_number',
+ ),
+ ]

88. User
email
phone_number
User
email
phone_number

89. Run
migrations
1
User
email
User
email
phone_number

90. Run
migrations
1
User
email
User
email
phone_number

91. Run
migrations
Deploy code
1
2
User
email
User
email

92. class User(BaseModel):
email = models.EmailField(max_length=254, unique=True)
- phone_number = models.CharField(max_length=50)
+class Migration(migrations.Migration):
+ operations = [
+ migrations.RemoveField(
+ model_name='user',
+ name='phone_number',
+ ),
+ ]

93. class User(BaseModel):
email = models.EmailField(max_length=254, unique=True)
- phone_number = models.CharField(max_length=50)
+class Migration(migrations.Migration):
+ operations = [
+ migrations.RemoveField(
+ model_name='user',
+ name='phone_number',
+ ),
+ ]
Commit and
deploy first.

94. class User(BaseModel):
email = models.EmailField(max_length=254, unique=True)
- phone_number = models.CharField(max_length=50)
+class Migration(migrations.Migration):
+ operations = [
+ migrations.RemoveField(
+ model_name='user',
+ name='phone_number',
+ ),
+ ]
Commit and
deploy first.
Then commit
and deploy.

96. User
email
phone_number
User
email
phone_number

97. User
email
phone_number
User
email
phone_number
Run migrations
(None)
1

98. Deploy code
(model change only)2
User
email
phone_number
User
email
Run migrations
(None)
1

99. Deploy code
(model change only)
Run migrations
(remove field)
2
3
User
email
User
email
Run migrations
(None)
1

100. Deploy code
(model change only)
Run migrations
(remove field)
2
3
User
email
User
email
Run migrations
(None)
1
Deploy code
(None)
4

103. class User(BaseModel):
- first_name = models.CharField(max_length=50)
- first_name = models.CharField(max_length=50, db_index=True)

104. class User(BaseModel):
- first_name = models.CharField(max_length=50)
- first_name = models.CharField(max_length=50, db_index=True)
+class Migration(migrations.Migration):
+ operations = [
+ migrations.AlterField(
+ model_name='user',
+ name='first_name',
+ field=models.CharField(max_length=50, db_index=True),
+ ),
+ ]

105. $ ./manage.py sqlmigrate accounts 0004

106. $ ./manage.py sqlmigrate accounts 0004
BEGIN;
CREATE INDEX "accounts_user_first_name_a03f23825d126a2_uniq" ON
"accounts_user" ("first_name");
COMMIT;

107. $ ./manage.py sqlmigrate accounts 0004
BEGIN;
CREATE INDEX "accounts_user_first_name_a03f23825d126a2_uniq" ON
"accounts_user" ("first_name");
COMMIT;
Locks the
entire table!

108. CREATE INDEX CONCURRENTLY "accounts_user_first_name" ON
"accounts_user" ("first_name");

109. CREATE INDEX CONCURRENTLY "accounts_user_first_name" ON
"accounts_user" ("first_name");
Running this
is appropriate.

110. $ aptible ssh --app vida-webserver
$ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.

111. $ aptible ssh --app vida-webserver
$ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> CREATE INDEX CONCURRENTLY "accounts_user_first_name" ON
"accounts_user" ("first_name");
CREATE_INDEX

112. $ aptible ssh --app vida-webserver
$ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> CREATE INDEX CONCURRENTLY "accounts_user_first_name" ON
"accounts_user" ("first_name");
CREATE_INDEX
vida=> d accounts_user

113. $ aptible ssh --app vida-webserver
$ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> CREATE INDEX CONCURRENTLY "accounts_user_first_name" ON
"accounts_user" ("first_name");
CREATE_INDEX
vida=> d accounts_user
vida=> INSERT INTO django_migrations (app, name, applied) VALUES
('accounts', '0004_auto_20160830_1124', current_timestamp);
INSERT 0 1

114. $ aptible ssh --app vida-webserver
$ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> CREATE INDEX CONCURRENTLY "accounts_user_first_name" ON
"accounts_user" ("first_name");
CREATE_INDEX
vida=> d accounts_user
vida=> INSERT INTO django_migrations (app, name, applied) VALUES
('accounts', '0004_auto_20160830_1124', current_timestamp);
INSERT 0 1
vida=> SELECT * FROM django_migrations;

115. $ aptible ssh --app vida-webserver
$ ./manage.py dbshell
psql (9.4.1)
Type "help" for help.
vida=> CREATE INDEX CONCURRENTLY "accounts_user_first_name" ON
"accounts_user" ("first_name");
CREATE_INDEX
vida=> d accounts_user
vida=> INSERT INTO django_migrations (app, name, applied) VALUES
('accounts', '0004_auto_20160830_1124', current_timestamp);
INSERT 0 1
vida=> SELECT * FROM django_migrations;
Now it’s safe
to deploy.