ActiveRecord::AdapterNotSpecified database configuration does not specify adapter

You didn't show the command causing this query, but this could happen if you pass a string and not a symbol.

For example:

irb(main):001:0> ActiveRecord::Base.establish_connection("#{Rails.env}")
ActiveRecord::AdapterNotSpecified: database configuration does not specify adapter

But then if you use a symbol, it will work.

irb(main):001:0> ActiveRecord::Base.establish_connection("#{Rails.env}".to_sym)
=> #<ActiveRecord::ConnectionAdapters::ConnectionPool:0x007f2f484a32a0 #....

For you app to work locally you need to:

1. Install Postgresql on your machine
2. Create a database for your development needs (let's call it my_app_development)

3. Change your database.yml to:

   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: my_app_development
   

4. run rake db:migrate

Your database.yml should look something like this:

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
  username: my_username
  password: my_password

development:
  <<: *default
  database: "development_database_name"

test:
  <<: *default
  database: "test_database_name"

production:
  <<: *default
  database: "production_database_name"

Edit development_database_name to your local database name. Also edit my_username and my_password to your correct db username and password.