fixture_dependencies

fixture_dependencies is an advanced fixture loader, allowing the loading of models from YAML fixtures, along with their entire dependency graph. It has the following features:

  • Fixtures specify association names instead of foreign keys
  • Support both Sequel and ActiveRecord
  • Supports many_to_one/belongs_to, one_to_many/has_many, many_to_many/has_and_belongs_to_many, and has_one/one_to_one associations
  • Loads a fixture's dependency graph in such a manner that foreign key constraints aren't violated
  • Has a very simple API (FixtureDependencies.load(:model__fixture))
  • Handles almost all cyclic dependencies
  • Includes Rails and Sequel test helpers for Test::Unit (and a Sequel test helper for RSpec) that load fixtures for every test inside a transaction, so fixture data is never left in your database

Installation

  gem install fixture_dependencies

Source

Source is available via github:

  http://github.com/jeremyevans/fixture_dependencies

You can check it out with git:

  git clone git://github.com/jeremyevans/fixture_dependencies.git

Usage

With Rails/ActiveRecord/Test::Unit:

Add the following to test/test_helper.rb after "require 'test_help'":

  require 'fixture_dependencies/test_unit/rails'

This overrides the default test helper to load the fixtures inside transactions and to use FixtureDependencies to load the fixtures.

With Sequel/Test::Unit:

Somewhere before the test code is loaded:

  require 'fixture_dependencies/test_unit/sequel'

Make sure the test case classes use FixtureDependencies::SequelTestCase:

  class ModelTest < FixtureDependencies::SequelTestCase

This runs the test cases inside a Sequel transaction.

With Sequel/RSpec:

Somewhere before the test code is loaded:

  require 'fixture_dependencies/rspec/sequel'

This runs each spec inside a separate Sequel transaction.

With Minitest/Spec:

Somewhere before the test code is loaded:

  require 'fixture_dependencies/minitest_spec/sequel'

This runs each spec inside a separate Sequel transaction.

With other testing libraries:

You can just use FixtureDependencies.load to handle the loading of fixtures. The use of transactions is up to you. One thing you must do if you are not using the rails test helper is to set the fixture path for FixtureDependencies:

  FixtureDependencies.fixture_path = '/path/to/fixtures'

Changes to Rails default fixtures:

fixture_dependencies is designed to require the least possible changes to the default YAML fixtures used by Rails (well, at least Rails 1.2 and earlier). For example, see the following changes:

  OLD                       NEW
  asset1:                   asset1:
  id: 1                     id: 1
  employee_id: 2            employee: jeremy
  product_id: 3             product: nx7010
  vendor_id: 2              vendor: lxg_computers
  note: in working order    note: in working order

As you can see, you just replace the foreign key attribute and value with the name of the association and the associations name. This assumes you have an employee fixture with a name of jeremy, and products fixture with the name of nx7010, and a vendors fixture with the name lxg_computers.

Fixture files still use the table_name of the model. Note that you make sure to hard code primary key values for each fixture, as shown in the example above.

ERB Fixtures

Fixtures can also use ERB to preprocess the fixture file, useful if you need to do any programming inside the fixture file, such as looping to create multiple records. For the ERB support to be invoked, your fixture file should be named #table_name.yml.erb instead of #table_name.yml. You can mix ERB fixture files and regular fixture files, but you can not have an ERB fixture file and a regular fixture file for the same table (the regular fixture file will be used in that case).

Changes to the fixtures Class Method:

fixture_dependencies can still use the fixtures class method in your test:

  class EmployeeTest < Test::Unit::TestCase
    fixtures :assets
  end

In Rails default testing practices, the arguments to fixtures are table names. fixture_dependencies changes this to underscored model names. If you are using Rails' recommended table practices, this shouldn't make a difference.

It is recommended that you do not use the fixtures method, and instead load individual fixtures as needed (see below). This makes your tests much more robust, in case you want to add or remove individual fixtures at a later date.

Loading individual fixtures with fixtures class method

There is support for loading individual fixtures (and just their dependencies), using the following syntax:

  class EmployeeTest < Test::Unit::TestCase
    fixtures :employee__jeremy # Note the double underscore
  end

This would load just the jeremy fixture and its dependencies. I find this is much better than loading all fixtures in most of my test suites. Even better is loading just the fixtures you want inside every test method (see below). This leads to the most robust testing.

Loading fixtures inside test methods

I find that it is often better to skip the use of the fixtures method entirely, and load the fixtures I want manually in each test method. This provides for the loosest coupling possible. Here's an example:

  class EmployeeTest < Test::Unit::TestCase
    def test_employee_name
      # Load the fixture and return the Employee object
      employee = load(:employee__jeremy)
      # Test the employee
    end

    def test_employees
      # Load the fixtures and return two Employee objects
      employee1, employee2 = load(:employees=>[:jeremy, :karl])
      # Test the employees
    end

    def test_award_statistics
      #  Load all fixtures in both tables
      load(:employee_award__jeremy_first, :award__first)
      # Test the award_statistics method
      #  (which pulls data from the tables loaded above)
    end
  end

Don't worry about loading the same fixture twice, if a fixture is already loaded, it won't attempt to load it again.

Loading attributes only

You can load only the attributes of fixtures, without saving them with load_attributes. This is useful for occasions where you want to mutate attributes without having to create lots of fixtures or want to test code that is run before or after the database transaction (validations, model hooks).

# load_attributes responds like load, but without saving the record
fruit = load_attributes(:fruit__banana)
# test the behaviour before saving the record
fruit.save
# test the behaviour after saving the record

You can also use the build method for loading the attributes of a single record, merging the attributes passed as options. This is useful for testing changes in behaviour when mutating a single parameter:

old_banana   = build(:fruit__banana, :age=>'old')
fresh_banana = build(:fruit__banana, :age=>'new')
old_banana.must_be :rotten?
new_banana.wont_be :rotten?

one_to_many/many_to_many/has_many/has_and_belongs_to_many assocations

Here's an example of using has_one (logon_information), has_many (assets), and has_and_belongs_to_many (groups) associations.

  jeremy:
  id: 2
  name: Jeremy Evans
  logon_information: jeremy
  assets: [asset1, asset2, asset3]
  groups: [group1]

logon_information is a has_one association to another table which was split from the employees table due to database security requirements. Assets is a has_many association, where one employee is responsible for the asset. Employees can be a member of multiple groups, and each group can have multiple employees.

For has_* associations, after fixture_dependencies saves jeremy, it will load and save logon_information (and its dependencies...), it will load each asset in the order specified (and their dependencies...), and it will load all of the groups in the order specified (and their dependencies...). Note that there is only a load order inside a specific association, associations are stored in the same hash as attributes and are loaded in an arbitrary order.

many_to_many/has_and_belongs_to_many join table fixtures

Another change is that Rails defaults allow you to specify habtm join tables in fixtures. That doesn't work with fixture dependencies, as there is no associated model. Instead, you use a has_and_belongs_to_many association name in the the appropriate model fixtures (see above).

belongs_to/many_to_one polymorphic fixtures

ActiveRecord supports polymorphic associations by default. With Sequel, this is made via the sequel_polymorphic gem.

Here the mapping in Rails:

class Animal < ActiveRecord::Base
  has_many :fruits, as: :eater
end
class Fruit < ActiveRcord::Base
  belongs_to :eater, polymorphic: true
end

And here on Sequel:

require 'sequel_polymorphic'
class Animal < Sequel::Model
  plugin :polymorphic
  ony_to_many :fruits, as: :eater
end
class Fruit < Sequel::Model
  plugin :polymorphic
  many_to_one :eater, polymorphic: true
end

In both cases, the fixtures looks like:

animals.yml:

george:
  id: 1
  name: George

fruits.yml:

apple:
  id: 1
  name: Apple
  eater: george (Animal)

In your test, use something like this:

apple = load(:fruit__apple)
apple.eater.name.must_equal "George"

fixture_dependencies will set the eater association in Fruit instance george instance of Animal.

Cyclic dependencies

fixture_dependencies handles almost all cyclic dependencies. It handles all has_many, has_one, and habtm cyclic dependencies. It handles all self-referential cyclic dependencies. It handles all belongs_to cyclic dependencies except the case where there is a NOT NULL or validates_presence of constraint on the cyclic dependency's foreign key.

For example, a case that won't work is when employee belongs_to supervisor (with a NOT NULL or validates_presence_of constraint on supervisor_id), and john is karl's supervisor and karl is john's supervisor. Since you can't create john without a valid supervisor_id, you need to create karl first, but you can't create karl for the same reason (as john doesn't exist yet).

There isn't a generic way to handle the belongs_to cyclic dependency, as far as I know. Deferring foreign key checks could work, but may not be enabled (and one of the main reasons to use the plugin is that it doesn't require them). For associations like the example above (employee's supervisor is also an employee), setting the foreign_key to the primary key and then changing it later is an option, but database checks may prevent it. For more complex cyclic dependencies involving multiple model classes (employee belongs_to division belongs_to head_of_division when the employee is a member of the division and also the head of the division), even that approach is not possible.

Known issues

Currently, the plugin only supports YAML fixtures, but other types of fixtures would be fairly easy to add (send me a patch if you add support for another fixture type).

The plugin is significantly slower than the default testing method, because it loads all fixtures inside of a transaction (one per test method), where Rails defaults to loading the fixtures once per test suite (outside of a transaction), and only deletes fixtures from a table when overwriting it with new fixtures.

Instantiated fixtures are not available with this plugin. Instead, you should use load(:model__fixture_name).

Namespace Issues

By default, fixture dependencies is going to load the model with the camelized name in the symbol used. So for :foo_bar__baz, it's going to look for the fixture with name baz for the model FooBar. If your model is namespaced, such as Foo::Bar, this isn't going to work well. In that case, you can override the default mapping:

  FixtureDependencies.class_map[:bar] = Foo::Bar

and then use :bar__baz to load the fixture with name baz for the model Foo::Bar.

Troubleshooting

If you run into problems with loading your fixtures, it can be difficult to see where the problems are. To aid in debugging an error, add the following to test/test_helper.rb:

  FixtureDependencies.verbose = 3

This will give a verbose description of the loading and saving of fixtures for every test, including the recursive loading of the dependency graph.

Specs

The specs for fixture dependencies and be run with Rake. They require the sequel, activerecord, and sqlite3 gems installed. The default rake task runs the specs. You should run the spec_migrate task first to create the spec database.

Similar Ideas

Rails now supports something similar by default. Honestly, I'm not sure what the differences are.

fixture_references is a similar plugin. It uses erb inside yaml, and uses the foreign key numbers inside of the association names, which leads me to believe it doesn't support has_* associations.

License

fixture_dependencies is released under the MIT License. See the MIT-LICENSE file for details.

Author

Jeremy Evans code@jeremyevans.net