Code scalability is the capability to allow your software and processes to allow increase in productivity efficiently when you add new engineers. Scalable code design strategy: * Design for human in mind * Focus on productivity leak areas * How fat models are bad for code scalability

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Scalable Code Design
with slimmer Django models … and more
Dawa L. Sherpa
@dawalama
Lead Engineer, Rocketrip

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Rocketrip Clients Rewarding Employees for Great Behaviors
30% Average savings by
employees on travel.

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What is a Scalable Code Design ?
Why should we think about Scalable Code Design ?
What is your scalable code strategy ?

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Let’s define: Code Scalability Co-efficient (S)
T = Team Productivity
S = Scalability Co-efficient
N = Number of Engineers
I = Individual engineer’s
productivity
We can achieve code
scalability by increasing S
and I
=
T3 S =Ix x
T = S * ( N * I )

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S
I
Culture
Product
Management
Code
Architecture
Team Org
Tooling &
Process

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Where can we look to re-claim lost productivity ?
Productivity Leaks
Bugs & Refactoring [ Code design ]
Finding code [ Code design / tools ]
Checking & Testing work [ tools ]
Waiting [ conflict resolution, clarification etc. Code
design / tools ]
Others ( Meetings / task management etc )
Code
Architecture
Process &
Tooling

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Human vs Automan
✓ Econ vs Human : Richard H. Thaler, author of
Nudge/Misbehaving. Econ is rational, human is
not always rational.
✓ Automan vs Human : Automan is super logical,
human is mostly logical with human traits.
✓ Design architecture and process with human traits
in mind to improve productivity.
✓ Measure and question how engineers *feel* about
working on your code base ?
✓ Anxious
✓ Irritated
✓ Overwhelmed

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Improving S & I
✓ Decouple Code ( +S, +I, confidence, simpler, parallel work)
✓ Make code discoverable ( +S, +I, independence )
✓ Make code readable ( +S, +I, context, confidence)
✓ Make code testable (+S, +I, confidence, refactor, doc) *
✓ Show engineers system feedback ( +S, +I, confidence )
✓ Code can be reasoned about ( +S, confidence, speed)
✓ Engineers can deploy their completed tasks to production
system independently of unfinished work by others. ( +S, +I,
parallel work )

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Resources
Services
Rt Stack - Year ago
Django 1.5
MysqlApp App
App
Redis
External APIs
App App
Celery
RabbitMQ

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Services
RT Stack - Now
Django 1.9
Celery
Mysql
App App
App
Redis
External APIs
App App
React
SPA
SPA
SPA
SPA
API
Resources

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Example Django Fat Model
class Employee(db.Model):
…<field definitions>
…<managers>
…<property functions>
… activate helper functions
… account helper functions
… feature-x helper functions
… helper’s helper functions
class Employee(db.Model):
…<field definitions>
…<managers>
…<property functions>
… activate helper functions
… account helper functions
… feature-x helper functions
… helper’s helper functions
class Employee(db.Model):
…<field definitions>
…<managers>
…<property functions>
… activate helper functions
… account helper functions
… feature-x helper functions
… helper’s helper functions
fat-models.py

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Problems with Big Fat Django Models
✓ Everything is in one place. This is easier at first, but as your
software’s complexity increases, the contextual overload for the
engineering also increases exponentially.
✓ Data model and functionality is mixed. This marriage of data with
functionality makes sense if your application stays fairly simple and
small, but over time it becomes harder to refactor and understand.
✓ Easier to leak business logic into views, because it feels like views
are boilerplate using functions defined in your models.
✓ Your code structure does not distinguish features and functionality
of business systems. This adds translation complexity.

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Feature/Domain/Services
Example Django Slim Model Suggestion
class Employee(db.Model):
…<field definitions>
…<managers>
employee_account.py
…<related property functions>
… activate_account
… deactivate_account
… invite_user
employee_communication.py
…<related property functions>
… send_email
… send_txt_msg
… get_recent_messages
class Employee(db.Model):
…<field definitions>
…<managers>
…<property functions>
… activate helper functions
… account helper functions
… feature-x helper functions
… helper’s helper functions
employee_account_test.py
… test_activate_account
… test_deactivate_account
… test_invite_user
employee_communication_t
est.py
… test_send_email
… test_send_txt_msg
employee_common.py
…<related property functions>
… helper functions
employee_common_test.py
… test_common_func1

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Scalable Code : Human vs Automan
✓ Engineers can quickly conceptualize what the code is doing
• Readability ( Structure, Comments, Documentation,
Convention )
• Discoverability and inference ( Structure and Convention )
• Code can be reasoned about
✓ Engineers can evolve the system
• Refactor
• Visibility ( See the impact of their changes )
• Testability ( Validate assumptions for known states )
• Lose coupling, and grouping of logically related code

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Django x
RT Stack - Future - Microservices and beyond
Django x
Services
Django x
Celery
Mysql
App
Redis
External APIs
SPAAPI
Resources

16. Thank you
https://www.rocketrip.com/jobs