ruby-on-rails - レールで has_one リレーションを設定する

Question

これが機能しない理由がわかりません：

home_team = Team.find_by_name! home_team["name"]
away_team = Team.find_by_name! away_team["name"]

fixture.home_team = home_team
fixture.away_team = away_team

しかし、これは：

home_team = Team.find_by_name! home_team["name"]
away_team = Team.find_by_name! away_team["name"]

fixture.home_team_id = home_team.id
fixture.away_team_id = away_team.id

器具モデル:

class Fixture < ActiveRecord::Base
  has_one :home_team, foreign_key: 'home_team_id', class_name: 'Team'
  has_one :away_team, foreign_key: 'away_team_id', class_name: 'Team'
  ...
end

エラーは発生せず、行は保存されますがhome_team_id、away_team_id両方null...

誰か説明できますか？