wfgilman
Example of using Logger.metadata
Can someone provide an example of how you would attach metadata to a process using metatdata/1? If I have a GenServer say that accepts messages with a user_id. Where would I add the user_id to the metadata so that it’s printed in the logging? I’ve been searching the docs and online, but feel I need an example to drive home the concept.
Marked As Solved
smpallen99
Given the following entry in your config file:
config :logger, :console, format: "[$level] $metadata$message\n",
metadata: [:module, :function, :my_id]
You can do the following;
iex(1)> require Logger
Logger
iex(2)> Logger.info "test"
[info] module= function= test
:ok
iex(3)> Logger.info "test", [my_id: 123]
[info] module= function= my_id=123 test
:ok
iex(4)> Logger.metadata [my_id: 999]
:ok
iex(5)> Logger.info "another test"
[info] module= function= my_id=999 another test
:ok
iex(6)>
I added the :module and :function into the meta data, as an example of other meta data you might want. However, since I’m running it from iex, the don’t print anything useful.
Also Liked
smpallen99
@minhajuddin That is a good point. Glad you emphasis that.
It does, however, lend itself to a model where you have a process for each item in some collection. By setting metadata for that process at startup (presumedly with some id or name) its an easy way to identify the logs for the given item of the collection.
Exadra37
To log this I use in runtime.exs:
config :logger, :default_formatter,
# 18:29:12.987 | error | module=MyApp.Some.Module function=some_function/arity line=some_number | some message here
format: "$time | $level | $metadata | $message\n",
metadata: [
:request_id,
:module,
:function,
:line
]
wfgilman
This is exactly what I was looking for. Thank you!
minhajuddin
One thing to note about Logger.metadata is that it is set only for the current process. From the documentation
https://hexdocs.pm/logger/Logger.html#metadata/1
## Metadata
Metadata to be sent to the Logger can be read and written with the
Logger.metadata/0 and Logger.metadata/1 functions. For example, you can set
Logger.metadata([user_id: 13]) to add user_id metadata to the current process.
The user can configure the backend to chose which metadata it wants to print
and it will replace the $metadata value.
wfgilman
That’s the route I’ve gone thanks to your advice. Very helpful.
Popular in Questions
Other popular topics
Latest on Elixir Forum
Sponsor Spotlight
Develop your skills with books, videos, and courses.
Categories:
Sub Categories:
Forums
Our Sponsors
Build Elixir applications with speed and confidence.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Catch errors, track performance, monitor hosts and more.
Practical resources that improve the lives of professional developers.
Enabling companies to succeed by building software people love.
The deployment platform built for Elixir: PaaS ease, VPS control.
Courses that'll move you from confusion to "Aha, now I get it!"