specify gem version to be used with a specific gem? - ruby-on-rails

Question

This is more of a general question, I'm new to rails.
I trying to use a gem that requires an older version of json, json -v 1.6.5
other gems in my rails application depends on newer version of json, json -v 1.8
I'm wondering if it is possible to specify json version to be used with a specific gem?
Thank you

Answer 1

No it's impossible to use 2 versions of a gem at the same time.
Use 2 versions of gem at same time

Answer 2

If bundle update doesn't resolve the dependencies I would fork on of the gems you need to use the same version as the other and then point to my fork.
gem 'some_gem', git: 'https://github.com/user/My-Fork.git'

Answer 3

Each of your dependencies will have a version constraint and your project can only use one version of each gem.
The answer to your specific question is that yes, you can control the version of an indirect dependency by specifying which version to use directly in your gemfile. However, this version must satisfy the version constraint of the direct dependency.
A brief example. Let's say your gemfile looks like this:
source 'https://rubygems.org/'
gem 'somegem', '~> 1.0'
And your gemfile lock looks something like this (note, some parts omitted for brevity):
GEM
remote: https://rubygems.org/
specs:
somegem (1.0)
json (~> 1.8)
json (1.8)
The Gemfile.lock indicates that somegem is dependent on json and that the json version must be greater than or equal to 1.8 but less than 2.0 (read more about the ~> operator here).
If you want to use lets say json version 1.9, you can modify your gemfile or use bundler commands to update the version used in the lock file.
E.g.
source 'https://rubygems.org/'
gem 'somegem', '~> 1.0'
gem 'json' , '~> 1.9'
In your specific case, if you have two dependencies that use conflicting versions of an indirect dependency, the gems will be incompatible. However, this example is meant to show that you can specify the version of an indirect dependency IF it meets the constraint specified by the direct dependency.
Rails uses Bundler to manage Ruby dependencies. An overview of the gemfile would be a good place to start learning how to manage your project's dependencies.