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
your book suggests to use Image.toByteData() to convert image to bytes, however I get the following error: "the getter ‘toByteData’ isn’t...
New
I can’t setup the Rails source code. This happens in a working directory containing multiple (postgres) Rails apps.
With:
ruby-3.0.0
s...
New
@noelrappin
Running the webpack dev server, I receive the following warning:
ERROR in tsconfig.json
TS18003: No inputs were found in c...
New
On page 78 the following code appears:
<%= link_to ‘Destroy’, product,
class: ‘hover:underline’,
method: :delete,
data: { confirm...
New
The markup used to display the uploaded image results in a Phoenix.LiveView.HTMLTokenizer.ParseError error.
lib/pento_web/live/product_l...
New
The allprojects block listed on page 245 produces the following error when syncing gradle:
“org.gradle.api.GradleScriptException: A prob...
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
When running the program in chapter 8, “Implementing Combat”, the printout Health before attack was never printed so I assumed something ...
New
@mfazio23
I’m following the indications of the book and arriver ad chapter 10, but the app cannot be compiled due to an error in the Bas...
New
Is there any plan for volume 2? :slight_smile:
New
Other popular topics
Bought the Moonlander mechanical keyboard. Cherry Brown MX switches. Arms and wrists have been hurting enough that it’s time I did someth...
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
Start building native Android apps the modern way in Kotlin with Jetpack's expansive set of tools, libraries, and best practices. Learn h...
New
I ended up cancelling my Moonlander order as I think it’s just going to be a bit too bulky for me.
I think the Planck and the Preonic (o...
New
A few weeks ago I started using Warp a terminal written in rust. Though in it’s current state of development there are a few caveats (tab...
New
Author Spotlight
Mike Riley
@mriley
This month, we turn the spotlight on Mike Riley, author of Portable Python Projects. Mike’s book ...
New
zig/http.zig at 7cf2cbb33ef34c1d211135f56d30fe23b6cacd42 · ziglang/zig.
General-purpose programming language and toolchain for maintaini...
New
Big O Notation can make your code faster by orders of magnitude. Get the hands-on info you need to master data structures and algorithms ...
New
A concise guide to MySQL 9 database administration, covering fundamental concepts, techniques, and best practices.
Neil Smyth
MySQL...
New
Background
Lately I am in a quest to find a good quality TTS ai generation tool to run locally in order to create audio for some videos I...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /java
- /emacs
- /haskell
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /flutter
- /vscode
- /ash
- /html
- /opensuse
- /deepseek
- /zig
- /centos
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /django
- /deno
- /kubuntu
- /arch-linux
- /nodejs
- /spring
- /ubuntu
- /revery
- /manjaro
- /lua
- /julia
- /diversity
- /markdown
- /c
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!"
Publishing Linux Magazine, ADMIN, and MakerSpace for 25+ years.