Storing data inside a ruby gem, where / how to write files? - ruby-on-rails

Question

I've been working on a Ruby parser, that fetches data from different API sources, and compile this data into a clear read-to-use JSON file.
For my use case, i need to store the data i'm initially fetching from the different sources as i don't want to fetch them each time I use the code.
For now i'm writing the JSON i'm receiving from the API sources locally into different JSON files stored in a data folder where my ruby script is. Then i read those files again, parse them and generate my new formatted JSON file that i'm gonna use later in a Rails app.
For that matter i want to create a Gem from this ruby script, which i'm currently working on. Nevertheless i'm not sure to fully understand how and where i should store that data (the one i'm fetching and the one i'm generating).
For now i have tried to simply keep the code as is and simply try to write the file like so:
URI.open("path/to/where/i/wanna/store/file.json", "wb") do |file|
file << URI.open(fetched_data_url).read
end
But wherever i try to write the data i get a :
No such file or directory # rb_sysopen path/to/where/i/wanna/store/file.json
Which in a way does not surprise me that much as i expected it to work in different ways in the context of a Gem. But i'm still missing something here about how to handle this. I'm not sure to fully understand how that all works, especially when you use paths in a gem that will ultimately be used in a rails project.
So several questions here:
Whenever you use a path to write a file inside a Gem, is that path relative to the gem or to the project that will ultimately use that Gem? (and consequently will the file be written inside the project that uses the Gem?)
In that precise use case here, what should i do about it? Where and how do i store my data so that i can use it later? knowing that i need to store it as a JSON file and that for now any attempt of writing a file ends up with an error.
Any input on what i'm misunderstanding here would be much appreciated ! Thanks !

Answer 1

Whenever you use a path to write a file inside a Gem, is that path relative to the gem or to the project that will ultimately use that Gem?
There is nothing special about using file paths whether the code is part of a Gem or not.
path/to/where/i/wanna/store/file.json is a relative path, which means it is looked up relative to the current working directory of the user who started the script. That's nothing special about Gems, that's not even anything to do with Ruby. That is just how file paths work. Relative paths are relative to the current working directory, absolute paths are not.
Where and how do i store my data so that i can use it later?
This depends largely on the Operating System Environment. Different OS Environments have different conventions where to store what kind of files. E.g. your files look like they fit the definition of a cache and Windows has a dedicated folder for caches, as does macOS, as do Linux distributions that follow the Linux Standard Base, as do Desktop Environments that follow the Free Desktop Standards, as does Android, as does iOS, …
For example, the Free Desktop Group has the XDG Base Directory Specification, which defines directories for application state, application data, application cache, and many other things for XDG-compliant environments. Microsoft has similar specifications for Windows. The LSB has something to say as well.