FactoryGirl: why does attributes_for omit some attributes?

Short Answer:

By design, FactoryGirl's attribues_for intentionally omits things that would trigger a database transaction so tests will run fast. But you can can write a build_attributes method (below) to model all the attributes, if you're willing to take the time hit.

Original answer

Digging deep into the FactoryGirl documentation, e.g. this wiki page, you will find mentions that attributes_for ignores associations -- see update below. As a workaround, I've wrapped a helper method around FactoryGirl.build(...).attributes that strips id, created_at, and updated_at:

def build_attributes(*args)
  FactoryGirl.build(*args).attributes.delete_if do |k, v| 
    ["id", "created_at", "updated_at"].member?(k)
  end
end

So now:

>> build_attributes(:premise_group)
=> {"name"=>"PremiseGroup_21", "user_id"=>29, "is_visible"=>false, "is_open"=>false}

... which is exactly what's expected.

update

Having absorbed the comments from the creators of FactoryGirl, I understand why attributes_for ignores associations: referencing an association generates a call to the db which can greatly slow down tests in some cases. But if you need associations, the build_attributes approach shown above should work.

I think this is a slight improvement over fearless_fool's answer, although it depends on your desired result.

Easiest to explain with an example. Say you have lat and long attributes in your model. On your form, you don't have lat and long fields, but rather lat degree, lat minute, lat second, etc. These later can converted to the decimal lat long form.

Say your factory is like so:

factory :something
  lat_d 12
  lat_m 32
  ..
  long_d 23
  long_m 23.2
end

fearless's build_attributes would return { lat: nil, long: nil}. While the build_attributes below will return { lat_d: 12, lat_m: 32..., lat: nil...}

def build_attributes
  ba = FactoryGirl.build(*args).attributes.delete_if do |k, v| 
    ["id", "created_at", "updated_at"].member?(k)
  end
  af = FactoryGirl.attributes_for(*args)
  ba.symbolize_keys.merge(af)
end