Foxy Fixtures Explained

As of October, 2006, Rails integrated a plugin called Foxy Fixtures into the core API.

This makes it easier to write fixtures–no more worrying about IDs! What’s more, created_on and updated_on are automatically populated with today’s date! Instead of writing this:


# libraries.yaml
central_library:
id: 1
city: "Toronto"
created_on: <%= Date::today %>


You can write this:
# libraries.yaml
central_library:
city: “Toronto”

Nice, eh? Even better--if you have a multiplicity association (has_many, belongs_to, or has_and_belongs_to_many), your fixture goes from:


# books.yaml
agile_rails:
title: "Agile Web Development with Rails"
published: 2007
library_id: 1


To:


# books.yaml
agile_rails:
title: "Agile Web Development with Rails"
published: 2007
library: central_library


Notice how much more readable and maintainable it is! No more IDs polluting your fixtures, no more worries about putting the right or wrong ID; but simple, easy-to-use names.

Now, if you try this, out-of-the-box, it might not work--there's a tricky gotcha--all the IDs have changed.

You might have assumed, from the example, that with Foxy Fixtures, central_library has an ID of one.

You'd be wrong if you thought that.

What is the ID? If you look through the test log, you'll see something like this:


...
Library Load (0.000000) SELECT * FROM `libraries` WHERE (`libraries`.`id` = 9523826)
...


What does that mean? It means, quite simply, that the IDs are assigned through some mechanism out of our control--that you cannot depend on the IDs being anything. (The IDs are not completely random, though; the same fixture will always have the same ID.) The good news is, you don't really care what the ID is--because you can reference the fixture by name!

And that's fixtures in a nutshell. So take a few minutes now to modify your Rails fixtures to take advantage of this--the ease (and maintainability) of Foxy Fixtures over regular ol' fixtures makes it an outstanding addition to the core Rails API.