Mysql2::Error: Duplicate entry '' for key 'index_admin_users_on_email' Ruby on Rails Error

Question

I am trying to run ruby on rails code that I got from github and I ended up installing mysql using homebrew and then also ended up installing it directly from http://dev.mysql.com/. It was only then that when I used rake in the application file that the tests began to run. However, now I keep getting this Mysql2::Error: Duplicate entry and I don't understand why. Could it be the fact that I have two mysqls located two different places on my computer? I am not really sure what is causing this problem because all the tables are empty. How can I fix this problem? Thank you for helping. I am new to Ruby on Rails and Mysql.

The stack looks like the following:

HomeControllerTest
 test_should_get_index                                               ERROR
    Mysql2::Error: Duplicate entry '' for key 'index_admin_users_on_email': INSERT INTO `admin_users` (`created_at`, `updated_at`, `id`) VALUES ('2011-12-09 09:33:30', '2011-12-09 09:33:30', 298486374)
    STDERR:
    Exception `ActiveRecord::RecordNotUnique' at /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/connection_adapters/mysql2_adapter.rb:283:in `query'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/connection_adapters/mysql2_adapter.rb:283:in `block in execute'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/connection_adapters/abstract_adapter.rb:244:in `block in log'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.1.3/lib/active_support/notifications/instrumenter.rb:21:in `instrument'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/connection_adapters/abstract_adapter.rb:239:in `log'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/connection_adapters/mysql2_adapter.rb:283:in `execute'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/connection_adapters/abstract/database_statements.rb:302:in `insert_fixture'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:486:in `block (5 levels) in create_fixtures'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:485:in `each'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:485:in `block (4 levels) in create_fixtures'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:484:in `each'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:484:in `block (3 levels) in create_fixtures'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:476:in `each'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:476:in `block (2 levels) in create_fixtures'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/connection_adapters/abstract/database_statements.rb:192:in `transaction'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:475:in `block in create_fixtures'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/connection_adapters/mysql2_adapter.rb:202:in `disable_referential_integrity'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:460:in `create_fixtures'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:924:in `load_fixtures'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.1.3/lib/active_record/fixtures.rb:890:in `setup_fixtures'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.1.3/lib/active_support/callbacks.rb:413:in `_run_setup_callbacks'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.1.3/lib/active_support/callbacks.rb:81:in `run_callbacks'
    /Users/nick01s/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.1.3/lib/active_support/testing/setup_and_teardown.rb:34:in `run'

Answer 1

For anyone else getting this error, this came down to (for me) installing active_admin into an existing project.

The admin_users.yml fixture file was initialised by rails to insert two empty records:

# Read about fixtures at http://api.rubyonrails.org/classes/ActiveRecord/Fixtures.html

# This model initially had no columns defined.  If you add columns to the
# model remove the '{}' from the fixture names and add the columns immediately
# below each fixture, per the syntax in the comments below
#
one: {}
# column: value
#
two: {}
#  column: value

Commenting out/removing these empty insertions fixed the error for me.

Answer 2

It's unlikely that the two installations of mysql are causing this problem. Rails should only connect to one database. You may not know which one it is connecting to, but it takes extra work to get it to connect to more than one db.

I've seen that duplicate key error before when the fixtures in tests were bad.

In your stack trace, it looks to me like something (fixtures or factories) is trying to create an admin_user without a required field. Twice.

The second time it's throwing an exception because the index is set to unique.