Find or create record through factory_girl association

You can to use initialize_with with find_or_create method

FactoryGirl.define do
  factory :group do
    name "name"
    initialize_with { Group.find_or_create_by_name(name)}
  end

  factory :user do
    association :group
  end
end

It can also be used with id

FactoryGirl.define do
  factory :group do
    id     1
    attr_1 "default"
    attr_2 "default"
    ...
    attr_n "default"
    initialize_with { Group.find_or_create_by_id(id)}
  end

  factory :user do
    association :group
  end
end

For Rails 4

The correct way in Rails 4 is Group.find_or_create_by(name: name), so you'd use

initialize_with { Group.find_or_create_by(name: name) } 

instead.

I ended up using a mix of methods found around the net, one of them being inherited factories as suggested by duckyfuzz in another answer.

I did following:

# in groups.rb factory

def get_group_named(name)
  # get existing group or create new one
  Group.where(:name => name).first || Factory(:group, :name => name)
end

Factory.define :group do |f|
  f.name "default"
end

# in users.rb factory

Factory.define :user_in_whatever do |f|
  f.group { |user| get_group_named("whatever") }
end