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
Running the examples in chapter 5 c under pytest 5.4.1 causes an AttributeError: ‘module’ object has no attribute ‘config’.
In particula...
New
When I try the command to create a pair of migration files I get an error.
user=> (create-migration "guestbook")
Execution error (Ill...
New
Hi @venkats,
It has been mentioned in the description of ‘Supervisory Job’ title that 2 things as mentioned below result in the same eff...
New
This isn’t directly about the book contents so maybe not the right forum…but in some of the code apps (e.g. turbo/06) it sends a TURBO_ST...
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
I think I might have found a problem involving SwitchCompat, thumbTint, and trackTint.
As entered, the SwitchCompat changes color to hol...
New
I’m not quite sure what’s going on here, but I’m unable to have to containers successfully complete the Readiness/Liveness checks. I’m im...
New
Hey there,
I’m enjoying this book and have learned a few things alredayd. However, in Chapter 4 I believe we are meant to see the “>...
New
The allprojects block listed on page 245 produces the following error when syncing gradle:
“org.gradle.api.GradleScriptException: A prob...
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
Other popular topics
Reading something? Working on something? Planning something? Changing jobs even!?
If you’re up for sharing, please let us know what you’...
New
If it’s a mechanical keyboard, which switches do you have?
Would you recommend it? Why?
What will your next keyboard be?
Pics always w...
New
I’m thinking of buying a monitor that I can rotate to use as a vertical monitor?
Also, I want to know if someone is using it for program...
New
Design and develop sophisticated 2D games that are as much fun to make as they are to play. From particle effects and pathfinding to soci...
New
I know that -t flag is used along with -i flag for getting an interactive shell. But I cannot digest what the man page for docker run com...
New
You might be thinking we should just ask who’s not using VSCode :joy: however there are some new additions in the space that might give V...
New
Rust is an exciting new programming language combining the power of C with memory safety, fearless concurrency, and productivity boosters...
New
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
Develop, deploy, and debug BEAM applications using BEAMOps: a new paradigm that focuses on scalability, fault tolerance, and owning each ...
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
- /zig
- /centos
- /deepseek
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /django
- /deno
- /kubuntu
- /arch-linux
- /nodejs
- /revery
- /ubuntu
- /spring
- /manjaro
- /julia
- /lua
- /diversity
- /markdown
- /v
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.