Ruby on Rails - Counting goals of a team in many matches

I've got a Match model and a Team model.

I want to count how many goals a Team scores during the league (so I have to sum all the scores of that team, in both home_matches and away_matches).

How can I do that? What columns should I put into the matches and teams database tables?


I'd assume your Match model looks something like this:

belongs_to :home_team, class_name:"Team"
belongs_to :away_team, class_name:"Team"

attr_accessible :home_goal_count, :away_goal_count

If so, you could add a method to extract the number of goals:

def goal_count
    home_matches.sum(:home_goal_count) + away_matches.sum(:away_goal_count)

Since this could be expensive (especially if you do it often), you might just cache this value into the team model and use an after_save hook on the Match model (and, if matches ever get deleted, then an after_destroy hook as well):

after_save :update_team_goals

def update_team_goals
    home_team.update_attribute(:goal_count_cache, home_team.goal_count)
    away_team.update_attribute(:goal_count_cache, away_team.goal_count)

Since you want to do this for leagues, you probably want to add a belongs_to :league on the Match model, a league parameter to the goal_count method (and its query), and a goal_count_cache_league column if you want to cache the value (only cache the most recently changed with my suggested implementation, but tweak as needed).

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