# When rails fixtures and namespaces collide

Testing helps Rails apps work properly and stops bugs. Fixtures are a useful testing tool. But fixtures can cause problems when models are namespaced.

Say your app has a regular `Vehicle` model and a namespaced `Vehicles::Car` model. By convention, you'd think to place the fixtures in `vehicles.yml` and `vehicles/cars.yml`, respectively.

Doesn't work. Rails tries to load the fixtures from `vehicles/cars.yml` into `Vehicle`.

Here is why: Rails uses both the fixture file name and path to find the right model. `vehicles.yml` goes to `Vehicle` based on the name. But so does `vehicles/cars.yml` based on the path.

Don't just rename your model classes or namespaces to work around this.

Instead, move `vechicles/cars.yml` to `vehicles_cars.yml` (ie, it must not be in the `vechicles` folder), and add these lines at the top of the file:

```yaml
_fixture: model
  class: Vehicles::Car
```

Now rails loads `vehicles_cars.yml` into `Vehicles::Car`, avoiding the collision.

In summary:

* Rails matches fixtures using name and path
    
* Collisions happen when name of one class matches the path of another
    
* Specify the model class explicitly rather than renaming your classes and namespaces
    

Explicit model classes remove guesswork. Fixtures load properly. Tests run cleanly. Careful fixture setup prevents headaches.