Rails: No connection pool for ActiveRecord::Base

Question

I'm trying to use rails 4.2.6 to develop an app. I'm trying to use postgres for database. Server starts fine but when I try loading a page it throws this "No connection pool for ActiveRecord::Base" error.

What could it be?

EDIT

The pg gem wasn't working properly. I had to comment it before starting the server and then uncomment it from my GemFile afterwards. I realized that I was using Ruby 2.3 instead of Ruby 2.0 (as intended). I removed ruby 2.3 and set up everything under ruby 2.0 environment. It's now working properly.

I had read somewhere that there were some issues with the 'pg' gem in newer Rails releases, requiring people to use 'gem install pg --pre' instead for installing the gem. I tried that, but then my app was requiring the 'pg' gem in my GemFile and, well, the problem stated above showed up again.

This is how my database.yml file ended up:

  default: &default
     adapter: postgresql
     encoding: unicode
     host: localhost
     username: -------
     password: -------
     pool: 5

  development:
     <<: *default
     database: myDbName

Answer 1

If you are experiencing this error from a rake task, chances are you are not running the :environment task before your task.

Changing:

task :task_name do
end

to:

task task_name: :environment do
end

Should fix the issue.

Answer 2

This issue arises when the server cannot find the corresponding database it depends on to pull data from.

I had same issue from my end, I updated my version of Sqlite3, and it was higher than the version that the current Puma Server version supports.

I simply had to uninstall the Sqlite3 version, and then install the version supported by the current version of Puma Server.

gem uninstall sqlite3

This will uninstall the updated version of Sqlite3, and then you run the code below stating the version supported by your current server.

gem install sqlite3

Or you can as well open your Gemfile, and then include the version for the database that you are using

gem 'sqlite3', '~> 1.3.6' 

N/B: The sqlite3 version is the most current version as at the time of writing this answer

And then run

bundle update

to install the version of the database that you specified.

That's all.

I hope this helps.

Answer 3

For PostgreSQL your database.yml file should look something like that:

default: &default
  adapter: postgresql
  encoding: unicode
  # For details on connection pooling, see rails configuration guide
  # http://guides.rubyonrails.org/configuring.html#database-pooling
  pool: 5

development:
  <<: *default
  database: your_db_name

Also make sure that you have the gem installed: in your Gemfile:

gem 'pg'

Finally, restart your server.

Hope that helps

Edit: I almost forgot, make sure you have your PostgresSQL running, check this link for download and setup.

Answer 4

Check the database.yml if all settings are ok. If its the first time and you didn't create the database yet use this command to create the database

rake db:create

If the database already exists try reset the db migrations,

rake db:migrate:reset

Hope it'll solve the problem. Go to rails console and try something to check if its working or not.