Modular Design in Elixir

A talk about modular software design given at 9th Poznań Elixir Meetup

Transcript

1. mkaszubowski94
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3. mkaszubowski94 Maciej Kaszubowski THE BIG BALL OF NOUNS
4. mkaszubowski94 Maciej Kaszubowski MODULAR DESIGN IN ELIXIR
5. mkaszubowski94 Functional Programming
6. mkaszubowski94 immutability no side effects explicit arguments
7. mkaszubowski94 immutability no side effects explicit arguments simpler code
8. mkaszubowski94 and yet…
9. mkaszubowski94 time development progress complexity
10. mkaszubowski94 why is that?
11. mkaszubowski94 f(x) explicit input explicit output what we want
12. mkaszubowski94 f(x) input output what we want g(x) output
13. mkaszubowski94 input output what we have
14. mkaszubowski94 This means a single table (or a small group of them), *not* the entire DB ( )
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19. mkaszubowski94 on a higher level, our systems are not very functional
20. mkaszubowski94 Database mutable state shared dependency complexity
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22. mkaszubowski94 Object Object Object Object Object Object SHARED STATE SHARED STATE
23. mkaszubowski94 if we don’t accept shared state for simple objects, why it’s ok to do this on a system level?
24. mkaszubowski94 “In functional programming, you don’t need any design patterns”
25. mkaszubowski94 let’s not forget the good parts of Object Oriented design
26. mkaszubowski94 what can we do about it?
27. mkaszubowski94 https://www.confluent.io/blog/event-sourcing-cqrs-stream-processing-apache-kafka-whats-connection/ CQRS
28. mkaszubowski94 Domain Driven Design
29. mkaszubowski94 Actor Model https://www.brianstorti.com/the-actor-model/
30. mkaszubowski94 these are risky
31. mkaszubowski94 relational DB is still the safest solution
32. mkaszubowski94 Maciej Kaszubowski Modular Software Design
33. mkaszubowski94 1972
34. mkaszubowski94 One big problem
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38. mkaszubowski94 Modular design smaller, simpler modules strong boundaries low coupling
39. mkaszubowski94 Each module can be understood in isolation modified in isolation tested in isolation refactored in isolation
40. mkaszubowski94 ok, but how?
41. mkaszubowski94 Maciej Kaszubowski Example Project
42. mkaszubowski94 create a new job name image url price publish John Alchemist create new job manage jobs find a job logout description date
43. mkaszubowski94 your jobs John Alchemist create new job manage jobs find a job logout my awesome job accept my other job cancel accept cancel yet another one publish and one more accepted this didn’t go well canceled
44. mkaszubowski94 browse jobs John Alchemist create new job manage jobs find a job logout my awesome job my other job yet another one and one more filters 100$ 50$ 3500$ 99$ xxxx yyy zzz search
45. mkaszubowski94 start this job John Alchemist create new job manage jobs find a job logout my awesome job Don’t ask, you’ll get paid start a job https://example.com/jobs/1234
46. mkaszubowski94 defmodule ModularElixir.Job do use Ecto.Schema schema "jobs" do field :name, :string field :description, :string field :image_url, :string field :price, :integer field :datetime, :utc_datetime belongs_to :creator, ModularElixir.User belongs_to :contractor, ModularElixir.User end end
47. mkaszubowski94 JobService - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish()
48. mkaszubowski94 create a new job name image url price continue John Alchemist create new job manage jobs find a job logout description date
49. mkaszubowski94 pay for job pay 110$ John Alchemist create new job manage jobs find a job logout my awesome job job price………….………..100$ fee (10%)…………………….10$ total……………………………..110$ Don’t ask, you’ll get paid Your job will be published after the payment
50. mkaszubowski94 defmodule ModularElixir.Job do use Ecto.Schema schema "jobs" do field :name, :string field :description, :string field :image_url, :string field :paid, :boolean field :price, :integer field :datetime, :utc_datetime belongs_to :creator, ModularElixir.User belongs_to :contractor, ModularElixir.User end end
51. mkaszubowski94 JobService - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create()
52. mkaszubowski94 start this job John Alchemist create new job manage jobs find a job logout my awesome job Don’t ask, you’ll get paid start a job https://example.com/jobs/my-awesome-job
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54. mkaszubowski94 JobService - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug()
55. mkaszubowski94 browse jobs John Alchemist create new job manage jobs find a job logout my awesome job my other job yet another one and one more filters 100$ 50$ 3500$ 99$ xxxx yyy zzz search Upcoming job Job starting in 54 minutes ! x
56. mkaszubowski94 defmodule ModularElixir.Job do use Ecto.Schema schema "jobs" do field :name, :string field :description, :string field :image_url, :string field :paid, :boolean field :slug, :string field :started, :boolean field :price, :integer field :datetime, :utc_datetime belongs_to :creator, ModularElixir.User belongs_to :contractor, ModularElixir.User end end
57. mkaszubowski94 JobService - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug() - send_reminder()
58. mkaszubowski94 jobs JobService UserService users join (jobs_count) Payments preload jobs Chat Service JobSubtask Service
59. mkaszubowski94 jobs JobService UserService users join (jobs_count) Payments JobSubtask Service preload jobs Chat Service JOB USER CONVERSATION MESSAGE PAYMENT SUBTASK
60. mkaszubowski94 In most projects: • few nouns • a lot of interactions between them • logic is organised around the nouns • a lot of coupling as a result
61. mkaszubowski94 nouns are not universal
62. mkaszubowski94 defmodule ModularElixir.Job do use Ecto.Schema schema "jobs" do field :name, :string field :description, :string field :image_url, :string field :paid, :boolean field :slug, :string field :started, :boolean field :price, :integer field :datetime, :utc_datetime belongs_to :creator, ModularElixir.User belongs_to :contractor, ModularElixir.User end end
63. mkaszubowski94 Maciej Kaszubowski Extracting Behaviour
64. mkaszubowski94 the most important question: what is the desired outcome?
65. mkaszubowski94 1. what is the desired outcome? (what should happen?) 2. what data do I need to do this? 3. how can I get this data? 4. what should be exposed in the interface
66. mkaszubowski94 then, pull this out to a new, isolated module
67. mkaszubowski94 desired outcome module
68. mkaszubowski94 desired outcome module required data
69. mkaszubowski94 desired outcome module required data data source
70. mkaszubowski94 desired outcome module required data data source interface
71. mkaszubowski94 Maciej Kaszubowski Extracting Slugs
72. mkaszubowski94 start this job John Alchemist create new job manage jobs find a job logout my awesome job Don’t ask, you’ll get paid start a job https://example.com/jobs/my-awesome-job
73. mkaszubowski94 desired outcome: jobs should be accessible via human-friendly slugs
74. mkaszubowski94 required data: id-slug mapping for jobs
75. mkaszubowski94 SEO Context
76. mkaszubowski94 SEO Context slugs
77. mkaszubowski94 SEO Context slugs - register_slug() - get_id_by_slug() - get_current_slug() Interface:
78. mkaszubowski94 SEO Context - register_slug() - fetch_id_by_slug() - fetch_slug_by_id() slug resource_id resource_type my-awesome-job 1 job 1 1 job other-job 2 job 2 2 job slugs
79. mkaszubowski94 def show(conn, %{"job_id"  slug}) do job = slug  SeoContext.fetch_id_by_slug("job")  JobService.fetch_by_id() #  end
80. mkaszubowski94 def show(conn, %{"job_id"  slug}) do job = slug  SeoContext.fetch_id_by_slug("job")  JobService.fetch_by_id() #  end Plug?
81. mkaszubowski94 defmodule ModularElixir.Job do use Ecto.Schema schema "jobs" do field :name, :string field :description, :string field :image_url, :string field :paid, :boolean field :slug, :string field :started, :boolean field :price, :integer field :datetime, :utc_datetime belongs_to :creator, ModularElixir.User belongs_to :contractor, ModularElixir.User end end
82. mkaszubowski94 JobService - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug() - send_reminder()
83. mkaszubowski94 SEO Context • multiple slugs - easy to do • slugs for other resources - easy to do • slugs are resolved at the controller level • no slugs in domain logic
84. mkaszubowski94 no slugs in domain logic /api/jobs/my-awesome-job/subtasks from( s in Subtask, join: j in Job, on: s.job_id  j.id where: j.id  ^job_id, # … ) /api/jobs/1/subtasks
85. mkaszubowski94 Maciej Kaszubowski Extracting Notifications
86. mkaszubowski94 browse jobs John Alchemist create new job manage jobs find a job logout my awesome job my other job yet another one and one more filters 100$ 50$ 3500$ 99$ xxxx yyy zzz search Upcoming job Job starting in 54 minutes ! x
87. mkaszubowski94 desired outcome: notification is sent when a job is starting soon
88. mkaszubowski94 required data: job information device information
89. mkaszubowski94 Job Reminders upcoming_jobs devices
90. mkaszubowski94 Job Reminders upcoming_jobs - put_job() - remove_job() - register_device() devices Interface:
91. mkaszubowski94 Job Reminders upcoming_jobs - put_job() - remove_job() - register_device() devices Interface: Would probably require a transaction
92. mkaszubowski94 - register_device() Interface: Job Service search Job Reminders sent_reminders devices
93. mkaszubowski94 JobService - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug() - send_reminder()
94. mkaszubowski94 defmodule Notifications.Worker do use GenServer def handle_info(:work, state) do Notifications.send_notifications(now()) Process.send_after(self(), :work, @interval) {:noreply, state) end end
95. mkaszubowski94 defmodule Notifications do defmodule Logic do def send(jobs, datetime, already_sent) do Enum.each(jobs, fn job -> if starting_soon?(job) && not_sent_yet?(job, already_sent) do send_notification(job) end end) end end def send_notifications(datetime) do jobs = JobBoard.search(…) already_sent = fetch_already_sent() :ok = Logic.send(jobs, datetime, already_sent) end end
96. mkaszubowski94 Logic desired outcome Notifications Job Board required data data source
97. mkaszubowski94 logic is isolated from the data source
98. mkaszubowski94 Logic desired outcome Notifications required data events stream
99. mkaszubowski94 Logic desired outcome Notifications required data
100. mkaszubowski94 Logic desired outcome Notifications required data TESTS
101. mkaszubowski94 Maciej Kaszubowski Extracting Publishing
102. mkaszubowski94 JobService - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug() - send_reminder()
103. mkaszubowski94 problem: the same data model is used for reading and writing
104. mkaszubowski94 Job Publishing jobs Job Board jobs publish
105. mkaszubowski94 Job Publishing jobs Job Board jobs publish enforces job structure in params
106. mkaszubowski94 defmodule JobBoard do defmodule Job do @keys [:name, :description, ] @enforce_keys @keys defstruct @keys end def publish(%Job{} = job) do #  end end
107. mkaszubowski94 Job Publishing jobs Job Board jobs publish enforces job structure in params decides when the job is published
108. mkaszubowski94 Job Publishing jobs Job Board jobs upsert semantics decides what are the rules for editing a job publish
109. mkaszubowski94 defmodule ModularElixir.JobBoard.Job do use Ecto.Schema @schema_prefix “job_board” schema "jobs" do field :name, :string field :description, :string field :image_url, :string field :paid, :boolean field :slug, :string field :started, :boolean field :price, :integer field :datetime, :utc_datetime belongs_to :creator, ModularElixir.User belongs_to :contractor, ModularElixir.User end end
110. mkaszubowski94 JobService - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug() - send_reminder()
111. mkaszubowski94 JobService - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug() - send_reminder()
112. mkaszubowski94 JobBoard - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug() - send_reminder()
113. mkaszubowski94 Job Publishing - create() - get_drafts() - publish()
114. mkaszubowski94 JobBoard • can be tested in isolation (without mocking payments) • linear logic (without conditionals) • no risk of showing unpublished jobs
115. mkaszubowski94 JobPublishing • rules for publishing can be changed in isolation • can be used alongside other modules (e.g. Admins can publish jobs without paying)
116. mkaszubowski94 Job Board desired outcome JobBoard params are enforced by the interface Job Publishing
117. mkaszubowski94 Job Board desired outcome JobBoard params are enforced by the interface Admin
118. mkaszubowski94 Job Board desired outcome JobBoard params are enforced by the interface TESTS
119. mkaszubowski94 JobBoard - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug() - send_reminder()
120. mkaszubowski94 JobBoard jobs Ongoing Jobs jobs
121. mkaszubowski94 defmodule ModularElixir.JobBoard.Job do use Ecto.Schema @schema_prefix “job_board” schema "jobs" do field :name, :string field :description, :string field :image_url, :string field :paid, :boolean field :slug, :string field :started, :boolean field :price, :integer field :datetime, :utc_datetime belongs_to :creator, ModularElixir.User belongs_to :contractor, ModularElixir.User end end
122. mkaszubowski94 JobBoard - fetch_by_id() - search() - find_by_user_id() - accept() - cancel() - publish() - create() - find_by_slug() - send_reminder()
123. mkaszubowski94 Maciej Kaszubowski Outcomes
124. mkaszubowski94 JobService jobs
125. mkaszubowski94 JobService • multiple responsibilities • hard to change and understand • hard to test in isolation • grows with each new feature • hard to delete old features
126. mkaszubowski94 Job Publishing jobs Job Board jobs Reminders devices SEO slugs Ongoing Jobs jobs Job Archive jobs
127. mkaszubowski94 Smaller modules • clear responsibilities for each module • easy to change, refactor, understand • easy to test in isolation • tend to stay small • trivial to delete if no longer necessary
128. mkaszubowski94 focused on behaviour, not nouns
129. mkaszubowski94 nouns are not universal
130. mkaszubowski94 defmodule ModularElixir.Job do use Ecto.Schema schema "jobs" do field :name, :string field :description, :string field :image_url, :string field :paid, :boolean field :slug, :string field :started, :boolean field :price, :integer field :datetime, :utc_datetime belongs_to :creator, ModularElixir.User belongs_to :contractor, ModularElixir.User end end
131. mkaszubowski94 a “job” means something else in each module
132. mkaszubowski94 by splitting this, we make this explicit, rather than relying on some values
133. mkaszubowski94 the flow of the app is visible in the module structure and dependencies
134. mkaszubowski94 Job Publishing Job Board Ongoing Jobs Job Archive Reminders Payments
135. mkaszubowski94 the logic is more linear
136. mkaszubowski94 there are no (or fewer) dependency cycles
137. mkaszubowski94 the module hierarchy is much clearer
138. mkaszubowski94 Maciej Kaszubowski Criteria for modularising design
139. mkaszubowski94 start with a list of important decisions
140. mkaszubowski94 Important decisions • what are the rules for publishing jobs? • when/what notifications are sent? • which jobs are visible on job board? • how is a contractor chosen for each job? • what happens after a job is started? when the job ends? • how payments work? (when creator pays for job, how the contractor receives the money? do we allow coupons? credit cards? money transfers?) • …
141. mkaszubowski94 then, create a module for each decision
142. mkaszubowski94 Make each module • independent • easy to test • easy to understand • with a strong interface
143. mkaszubowski94 focus on behaviour, not data
144. mkaszubowski94 Maciej Kaszubowski Summary
145. mkaszubowski94 is this perfect?
146. mkaszubowski94 nope
147. mkaszubowski94 is this the best way?
148. mkaszubowski94 I have no idea
149. mkaszubowski94 it works for me
150. mkaszubowski94 but the main point is to start a discussion
151. mkaszubowski94 so argue with me over pizza
152. mkaszubowski94 Maciej Kaszubowski THANKS!