For the SQL libraries the fastest option will be to use `:transaction` as transactions are simply rolled back. If you can use this strategy you should. However, if you wind up needing to use multiple database connections in your tests (i.e. your tests run in a different process than your application) then using this strategy becomes a bit more difficult. You can get around the problem a number of ways.
One common approach is to force all processes to use the same database connection ([common ActiveRecord hack](http://blog.plataformatec.com.br/2011/12/three-tips-to-improve-the-performance-of-your-test-suite/)) however this approach has been reported to result in non-deterministic failures.
Another approach is to have the transactions rolled back in the application's process and relax the isolation level of the database (so the tests can read the uncommitted transactions).
So what is fastest out of `:deletion` and `:truncation`? Well, it depends on your table structure and what percentage of tables you populate in an average test. The reasoning is out of the scope of this README but here is a [good SO answer on this topic for Postgres](http://stackoverflow.com/questions/11419536/postgresql-truncation-speed/11423886#11423886).
Some people report much faster speeds with `:deletion` while others say `:truncation` is faster for them. The best approach therefore is it try all options on your test suite and see what is faster.
If you are using ActiveRecord then take a look at the [additional options](#additional-activerecord-options-for-truncation) available for `:truncation`.
## Dependencies
Because database_cleaner supports multiple ORMs, it doesn't make sense to include all the dependencies for each one in the gemspec. However, the DataMapper adapter does depend on dm-transactions. Therefore, if you use DataMapper, you must include dm-transactions in your Gemfile/bundle/gemset manually.
## How to use
```ruby
require 'database_cleaner'
DatabaseCleaner.strategy = :truncation
# then, whenever you need to clean the DB
DatabaseCleaner.clean
```
With the `:truncation` strategy you can also pass in options, for example:
Some strategies need to be started before tests are run (for example the `:transaction` strategy needs to know to open up a transaction). This can be accomplished by calling `DatabaseCleaner.start` at the beginning of the run, or by running the tests inside a block to `Database.cleaning`. So you would have:
At times you may want to do a single clean with one strategy.
For example, you may want to start the process by truncating all the tables, but then use the faster transaction strategy the remaining time. To accomplish this you can say:
```ruby
require 'database_cleaner'
DatabaseCleaner.clean_with :truncation
DatabaseCleaner.strategy = :transaction
# then make the DatabaseCleaner.start and DatabaseCleaner.clean calls appropriately
```
### Additional ActiveRecord options for Truncation
The following options are available for ActiveRecord's `:truncation` strategy _only_ for MySQL and Postgres.
*`:pre_count` - When set to `true` this will check each table for existing rows before truncating it. This can speed up test suites when many of the tables to be truncated are never populated. Defaults to `:false`. (Also, see the section on [What strategy is fastest?](#what-strategy-is-fastest))
*`:reset_ids` - This only matters when `:pre_count` is used, and it will make sure that a tables auto-incrementing id is reset even if there are no rows in the table (e.g. records were created in the test but also removed before DatabaseCleaner gets to it). Defaults to `true`.
*`:cache_tables` - When set to `true` the list of tables to truncate or delete from will only be read from the DB once, otherwise it will be read before each cleanup run. Set this to `false` if (1) you create and drop tables in your tests, or (2) you change Postgres schemas (`ActiveRecord::Base.connection.schema_search_path`) in your tests (for example, in a multitenancy setup with each tenant in a different Postgres schema). Defaults to `true`.
If you're using Capybara with RSpec and using an external browser (not using RackTest) you'll almost certainly need to use truncation rather than transactions for tests tagged `:js`.
If you're using Cucumber with Rails, just use the generator that ships with cucumber-rails, and that will create all the code you need to integrate DatabaseCleaner into your Rails project.
Otherwise, to add DatabaseCleaner to your project by hand, create a file `features/support/database_cleaner.rb` that looks like this:
```ruby
begin
require 'database_cleaner'
require 'database_cleaner/cucumber'
DatabaseCleaner.strategy = :truncation
rescue NameError
raise "You need to add database_cleaner to your Gemfile (in the :test group) if you wish to use it."
Usage beyond that remains the same with `DatabaseCleaner.start` calling any setup on the different configured connections, and `DatabaseCleaner.clean` executing afterwards.
<td> Connection specified as <code>:symbol</code> keys, loaded from <code>config/database.yml</code>. You may also pass in the ActiveRecord model under the <code>:model</code> key.</td>
One of my motivations for writing this library was to have an easy way to turn on what Rails calls "transactional_fixtures" in my non-rails ActiveRecord projects.
#### DatabaseCleaner is trying to use the wrong ORM
DatabaseCleaner has an autodetect mechanism where if you do not explicitly define your ORM it will use the first ORM it can detect that is loaded.
Since ActiveRecord is the most common ORM used that is the first one checked for.
Sometimes other libraries (e.g. ActiveAdmin) will load other ORMs (e.g. ActiveRecord) even though you are using a different ORM. This will result in DatabaseCleaner trying to use the wrong ORM (e.g. ActiveRecord) unless you explicitly define your ORM like so:
If you are using Postgres and have foreign key constraints, the truncation strategy will cause a lot of extra noise to appear on STDERR (in the form of "NOTICE truncate cascades" messages).
To silence these warnings set the following log level in your `postgresql.conf` file:
Due to an inconsistency in JRuby's implementation of Fibers, Sequel gives a different connection to `DatabaseCleaner.start` than is used for tests run between `.start` and `.clean`. This can be worked around by running your tests in a block like `DatabaseCleaner.cleaning { run_my_tests }` instead, which does not use Fibers.
### Model fails to load with Neo4j using transactions
When you are using [neo4j](https://github.com/neo4jrb/neo4j) gem it creates schema and reads indexes upon loading models. These operations can't be done during a transaction. You have to preload your models before DatabaseCleaner starts a transaction.
Add to your rails_helper or spec_helper after requiring database_cleaner:
```ruby
require 'database_cleaner'
Dir["#{Rails.root}/app/models/**/*.rb"].each do |model|
In rare cases DatabaseCleaner will encounter errors that it will log. By default it uses STDOUT set to the ERROR level but you can configure this to use whatever Logger you desire.
Here's an example of using the `Rails.logger` in `env.rb`:
