An error occurred while installing pg (0.12.2), and Bundler cannot continue

Question

I'm following the Michael Hartl Ruby on Rails Tutorial & there is a part where he is he he instructs you to update your Gemfile to include: ``` group :production do gem 'pg', '0.12.2' end ``` And then enter the below commands in your terminal: ``` bundle update bundle install --without production ``` When you run the bundle update command it throws back the below errors. ``` sample_app:$ bundle update Fetching gem metadata from https://rubygems.org/......... Fetching gem metadata from https://rubygems.org/.. Resolving dependencies... Using rake (10.0.3) Using i18n (0.6.4) etc [omitted lines for brevity] etc Using railties (3.2.12) Using coffee-rails (3.2.2) Installing diff-lcs (1.1.3) Using jquery-rails (2.0.2) Installing pg (0.12.2) Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension. /home/ross/.rvm/rubies/ruby-1.9.3-p392/bin/ruby extconf.rb checking for pg_config... no No pg_config... trying anyway. If building fails, please try again with --with-pg-con…

Accepted Answer

I'm following the same tutorial and I think it's redundant to run `update` without modifying existing dependency, but in this case it's even causing problems because `update` command has not `--without` argument.

I stumbled upon Rails 3 cheatsheet which mentions bundler workflow this way:

After adding or removing dependencies from Gemfile

- `$ bundle`

- Commit Gemfile and Gemfile.lock

After modifying existing dependency versions

- `$ bundle update`

- Commit Gemfile and Gemfile.lock

I read man pages for `bundle update` and tried RECOMMENDED WORKFLOW which consists of running `bundle update` after `bundle install`.

In my case (some output omitted):

```
$ bundle install --without production
Resolving dependencies...
Using rake (10.0.3)
...
Installing rspec-core (2.11.1)
Your bundle is complete!
Gems in the group production were not installed.             <-- check

$ bundle update
Resolving dependencies...
Using rake (10.0.3) 
...
Using uglifier (1.2.3) 
Your bundle is updated!
Gems in the group production were not installed.             <-- check
```

I tried it with new RVM gem set and everything was installed correctly.

After that `Gemfile.lock` contains `pg (0.12.2)` and deploying to Heroku works.

RECOMMENDED WORKFLOW

In general, when working with an application managed with bundler, you should use the following workflow:

After you create your Gemfile for the first time, run

`$ bundle install`

Check the resulting Gemfile.lock into version control

`$ git add Gemfile.lock`

When checking out this repository on another development machine, run

`$ bundle install`

When checking out this repository on a deployment machine, run

`$ bundle install --deployment`

After changing the Gemfile to reflect a new or update dependency, run

`$ bundle install`

Make sure to check the updated Gemfile.lock into version control

`$ git add Gemfile.lock`

If bundle install reports a conflict, manually update the specific gems that you changed in the Gemfile

`$ bundle update rails thin`

If you want to update all the gems to the latest possible versions that still match the gems listed in the Gemfile, run

`$ bundle update`

An error occurred while installing pg (0.12.2), and Bundler cannot continue

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