shaolang
Real-World Event Sourcing: `handle_command` for subtract doesn't make sense (pg 8)
The book implements handle_command/2 for :sub as follows:
def handle_command(%{value: val}, %{cmd: :sub, value: v}) do
%{event_type: :value_subtracted, max(@min_state_value, val - v)
end
The value in the created event is the result expected after subtraction, i.e., it is not the subtrahend. It can be reimplemented as follows instead:
def handle_command(%{value: val}, %{cmd: :sub, value: v) do
subtrahend = if(val >= v, do: v, else: val)
%{event_type: :value_subtracted, value: subtrahend}
end
First Post!
dmitrykleymenov
I’ve found the same issue, but think the code should be like:
def handle_command(%{value: val}, %{cmd: :sub, value: v}) do
%{event_type: :value_subtracted, value: min(val - @min_state_value, v)}
end
In this case we can use @min_state_value correctly(not only 0)
Popular Pragmatic Bookshelf topics
Title: Design and Build Great Web APIs - typo “https://company-atk.herokuapp.com/2258ie4t68jv” (page 19, third bullet in URL list)
Typo:...
New
I thought that there might be interest in using the book with Rails 6.1 and Ruby 2.7.2. I’ll note what I needed to do differently here.
...
New
Running mix deps.get in the sensor_hub directory fails with the following error:
** (Mix) No SSH public keys found in ~/.ssh. An ssh aut...
New
“The ProductLive.Index template calls a helper function, live_component/3, that in turn calls on the modal component. ”
Excerpt From: Br...
New
It seems the second code snippet is missing the code to set the current_user:
current_user: Accounts.get_user_by_session_token(session["...
New
Hi, I need some help, I’m new to rust and was learning through your book. but I got stuck at the last stage of distribution. Whenever I t...
New
Modern front-end development for Rails, second edition - Struggling to get the first chapter to work
After running /bin/setup, the first error was: The foreman' command exists in these Ruby versions: That was easy to fix: gem install fore...
New
@parrt
In the context of Chapter 4.3, the grammar Java.g4, meant to parse Java 6 compilation units, no longer passes ANTLR (currently 4....
New
I just bought this book to learn about Android development, and I’m already running into a major issue in Ch. 1, p. 20: “Update activity...
New
@mfazio23
Android Studio will not accept anything I do when trying to use the Transformations class, as described on pp. 140-141. Googl...
New
Other popular topics
Write Elixir tests that you can be proud of. Dive into Elixir’s test philosophy and gain mastery over the terminology and concepts that u...
New
Curious to know which languages and frameworks you’re all thinking about learning next :upside_down_face:
Perhaps if there’s enough peop...
New
New
This looks like a stunning keycap set :orange_heart:
A LEGENDARY KEYBOARD LIVES ON
When you bought an Apple Macintosh computer in the e...
New
In case anyone else is wondering why Ruby 3 doesn’t show when you do asdf list-all ruby :man_facepalming: do this first:
asdf plugin-upd...
New
The V Programming Language
Simple language for building maintainable programs
V is already mentioned couple of times in the forum, but I...
New
Saw this on TikTok of all places! :lol:
Anyone heard of them before?
Lite:
New
I am trying to crate a game for the Nintendo switch, I wanted to use Java as I am comfortable with that programming language. Can you use...
New
There appears to have been an update that has changed the terminology for what has previously been known as the Taskbar Overflow - this h...
New
Curious what kind of results others are getting, I think actually prefer the 7B model to the 32B model, not only is it faster but the qua...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /ruby
- /wasm
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /haskell
- /emacs
- /java
- /svelte
- /onivim
- /typescript
- /kotlin
- /crystal
- /c-plus-plus
- /tailwind
- /react
- /gleam
- /ocaml
- /flutter
- /elm
- /vscode
- /ash
- /html
- /opensuse
- /centos
- /zig
- /deepseek
- /php
- /scala
- /react-native
- /lisp
- /sublime-text
- /textmate
- /debian
- /nixos
- /agda
- /kubuntu
- /django
- /arch-linux
- /deno
- /revery
- /nodejs
- /ubuntu
- /spring
- /manjaro
- /diversity
- /lua
- /julia
- /markdown
- /slackware
Devtalk Sponsors
Practical resources that improve the lives of professional developers.
We build trusted fault-tolerant systems that scale to billions of users.
Real-time error tracking, performance insights, and observability for devs.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Develop your skills with books, videos, and courses.
Catch errors, track performance, monitor hosts and more.
Enabling companies to succeed by building software people love.
Courses that move you from confusion to "Aha, now I get it!"