5

Scnerio:

https://www.funtraker.com is listing movies, tv shows and games. On show page of each resource(Movie, Tv Show etc) we want to list down the related resources.

Schema:

class Movie < AR::Base
  has_many :resource_genres, as: :resource
  has_many :genres, through: :resource_genres
end

class ResourceGenre
  belongs_to :resource, polymorphic: true
end

Now I want to get a list of related movies based on matched genre( two movies are related if both has 'comedy` genre). And these related movies need to order by max number of matched genres.

Well here is sample movies and the expected output.

#Input
Movie         Genres
Movie 1:      horror, comedy, action, war
Movie 2:      action, thriller, crime, animation  
Movie 3:      comedy, war, action, thriller
Movie 4:      crime, animation, action, war

#Expected output
movie1.related_movies => [ movie3, movie2  ]
movie4.related_movies => [ movie2, remaining-three-movies-in-any-order ]
movie3.related_movies => [ movie1, movie2, movie4]

Hopefully question make sense.

UPDATE: Looking for SQL only solution. I don't need to cache the results in any another table.

4

2 回答 2

3

加入 with 后需要按电影 id 的组数排序， resource_genres看看下面的纯 SQL 方法：

方法 #1（单一查询）

双重加入resource_genres表格以维护自身类型 ID：

def related_movies
   Movie.select("movies.*, COUNT(*) AS group_count").
   joins(:resource_genres).
   joins("JOIN resource_genres rg ON rg.genre_id = resource_genres.genre_id").
   where("rg.resource_type = 'Movie' 
          AND rg.resource_id = ? 
          AND movies.id != ?", self.id, self.id).
   group('movies.id').
   order('group_count DESC')
end

方法 #2（2 个查询）

在单独的查询中genre_ids从 self中提取。resource_genres

def related_movies
   Movie.select("movies.*, COUNT(*) AS group_count").joins(:resource_genres).
   where("resource_genres.genre_id IN (?) 
         AND movies.id != ?", self.resource_genres.pluck(:genre_id), self.id).
   group('movies.id').
   order('group_count DESC')
end
于 2015-01-23T03:09:36.320 回答
0

如果您在 Rails 代码中找到解决方案，那么它可能会解决您的问题。

def related_movies
  scores_hash = {}
  Movie.joins(:resource_genres).where('resource_genres.genre_id' => resource_genres.pluck(&:genre_id)).where.not(id: self.id).distinct.find_each do |movie|
    scores_hash[movie] = (movie.resource_genres.pluck(:genre_id) & self.resource_genres.pluck(:genre_id)).count
  end
  Hash[scores_hash.sort_by { |movie, score| -score }].keys
end
于 2015-01-21T08:43:12.080 回答