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Sequel/ActiveRecord fixture loader that handles dependency graphs
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fixture_dependencies is a plugin that changes the way Rails uses fixtures in
the following ways:

- Fixtures can specify associations instead of foreign keys
- Supports belongs_to, has_many, has_one, and habtm associations
- Loads a fixture's dependencies (associations with other fixtures) before the
  fixture itself so that foreign key constraints aren't violated
- Can specify individual fixtures to load per test or test suite
- Loads fixtures on every test inside a transaction, so fixture information
  is never left in your database
- Handles almost all cyclic dependencies

To use, first install the plugin, then add the following to
test/test_helper.rb after "require 'test_help'":

  require 'fixture_dependencies_test_help'

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

Changes to Fixtures

fixture_dependencies is designed to require the least possible changes to
fixtures.  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.

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

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.

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 below).

Loading Individual Fixtures with fixtures

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
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.

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

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

has_* Assocations in Fixtures

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

  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

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.

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

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.  Rails actually did something similar starting with r2714, but it
was rolled back in r2730 due to speed issues.  See ticket #2404 on Rails' trac.

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


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 

  FixtureDependencies.verbose = 2
This will give a verbose description of the loading and saving of fixtures for
every test, including the recursive loading of all dependencies.

Similar Ideas

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.

Ticket #6424 on the Rails' trac also implements a similar idea, but it parses
the associations and changes them to foreign keys, which leads me to believe it
doesn't support has_* associations either.


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


Jeremy Evans <>
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