How can i make ruby on rails handle duplicate record errors from MySQL

Question

I have a unique index on multiple fields on my database. So if you try to call save on a duplicate record, it raises ActiveRecord::StatementInvalid and shows the mysql error. Is there a way to handle this within rails either by creating the unique constraint, or otherwise have it return a relevant error message when this happens?

heres the trace:

ActiveRecord::StatementInvalid: Mysql::Error: Duplicate entry '2010-12-09-2-0-1-1' for key 2: INSERT INTO `entries` (`rejected_at`, `created_at`, `comments`, `overtime`, `submitted_at`, `updated_at`, `time`, `approved`, `day`, `user_id`, `approved_at`, `job_id`, `submitted`, `rejected`) VALUES(NULL, '2010-12-09 21:50:46', NULL, 0, NULL, '2010-12-09 21:50:46', 2.0, NULL, '2010-12-09', 1, NULL, 1, NULL, NULL)
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb:219:in `log'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb:319:in `execute'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb:259:in `insert_sql'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb:329:in `insert_sql'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb:44:in `insert_without_query_dirty'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb:18:in `insert'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/base.rb:2901:in `create_without_timestamps'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/timestamp.rb:53:in `create_without_callbacks'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/callbacks.rb:266:in `create'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/base.rb:2867:in `create_or_update_without_callbacks'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/callbacks.rb:250:in `create_or_update'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/base.rb:2538:in `save_without_validation'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/validations.rb:1078:in `save_without_dirty'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/dirty.rb:79:in `save_without_transactions'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/transactions.rb:229:in `send'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/transactions.rb:229:in `with_transaction_returning_status'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb:136:in `transaction'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/transactions.rb:182:in `transaction'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/transactions.rb:228:in `with_transaction_returning_status'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/transactions.rb:196:in `save'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/transactions.rb:208:in `rollback_active_record_state!'
 from /home/cmatthews/src/cannon/vendor/rails/activerecord/lib/active_record/transactions.rb:196:in `save'

Answer 1

begin
  Event.create!(:name => 'Ironman Lanzarote 2011')
rescue ActiveRecord::RecordNotUnique => e
  # handle duplicate entry 
end

This works for me under Rails 3.

Answer 2

You can add a uniqueness constraint to your model so that the record returns with errors and is invalid.

For example (Rails 2):

class User < ActiveRecord::Base
  validates_uniqueness_of :email, :scope => [:name, :age]
end

or (Rails 3)

class User < ActiveRecord::Base
  validates :email, :uniqueness => {:scope => [:name, :age]}
end

This should result in the following:

user1 = User.create :email => "[email protected]", :name => "one", :age => 20
user2 = User.create :email => "[email protected]", :name => "one", :age => 20
user2.valid? # false