ruby on rails - Postgresql adapter (pg): could not connect to server

Question

I get this error every this I run my Rails app (It cannot connect to my local Postgresql)

/Users/leonardo/.rvm/gems/ruby-1.9.3-p362/gems/activerecord-3.2.11/lib/
active_record/connection_adapters/postgresql_adapter.rb:1208:in `initialize': 
could not connect to server: No such file or directory (PG::Error)
   Is the server running locally and accepting
connections on Unix domain socket "/var/pgsql_socket/.s.PGSQL.5432"?

I'm using Postgres.app that it's correctly running.

If I run

$ psql

I can login properly to Postgresql console.

$ which psql
 /Applications/Postgres.app/Contents/MacOS/bin/psql

Gemfile

source 'https://rubygems.org'
ruby "1.9.3"

gem 'rails', '3.2.11'
gem "pg"

database.yml

development:
  adapter: postgresql
  encoding: unicode
  username: leonardo
  password: 
  database: zapping
  port: 5432  

Postgresql (Console)

$ psql
leonardo=# l

Answer 1

Try adding host: localhost to your database.yml. (Based on: https://stackoverflow.com/a/10793186/919641)